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Refractive error

Refractive error is a prevalent eye condition in which the shape of the eyeball, cornea, or lens prevents light from focusing correctly on the retina, resulting in blurred or distorted vision at various distances.^[1] This condition encompasses several types, including myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia (age-related loss of near focus), and it affects the ability to see clearly for everyday activities.^[2] The primary causes of refractive errors stem from variations in the eye's anatomy, such as an eyeball that is too long or short, an irregularly curved cornea, or a lens that loses flexibility with age.^[1] These errors can be present from birth, develop during childhood or adolescence, or emerge later in life, particularly presbyopia after age 40 due to the lens's reduced elasticity.^[2] Globally, uncorrected refractive errors are the leading cause of vision impairment, affecting approximately 1 billion people with distance or near vision issues that could be easily corrected.^[3] In the United States alone, over 150 million individuals experience refractive errors, making them the most common type of vision problem.^[1] Common symptoms include blurry vision at near or far distances, double vision, eye strain, headaches, squinting, and difficulty focusing, which can impact daily tasks like reading, driving, or recognizing faces.^[1] In children, signs may manifest as poor school performance or excessive rubbing of the eyes, while adults might notice worsening vision during activities requiring precise focus.^[2] Diagnosis typically involves a comprehensive eye exam, including refraction testing to determine the precise error and prescribe corrective measures.^[1] Treatment options are highly effective and non-invasive in most cases, primarily consisting of corrective lenses such as eyeglasses or contact lenses to adjust how light enters the eye.^[2] For those seeking permanent solutions, refractive surgery like LASIK can reshape the cornea to improve focus, though it's not suitable for everyone and requires evaluation by an ophthalmologist.^[1] Regular eye examinations are recommended to monitor changes, with children needing checks every 1-2 years and adults over 40 every 1 to 4 years depending on age and risk factors.^[2] Despite available treatments, access remains a challenge in low-income settings, where only about 36% of those affected receive proper correction.^[4]

Anatomy and Physiology

Normal ocular anatomy

The human eye's optical system relies on several key anatomical structures to capture and focus incoming light rays onto the retina, enabling clear vision in an emmetropic (normal-sighted) eye. The cornea, a transparent, dome-shaped layer at the front of the eye, serves as the primary refractive surface, accounting for approximately two-thirds of the eye's total focusing power by bending light as it enters.^[5] Behind the cornea lies the anterior chamber, filled with aqueous humor, which maintains intraocular pressure and contributes to the refractive index of the ocular media.^[6] The iris, a colored muscular diaphragm surrounding the pupil, regulates the amount of light entering the eye by contracting or dilating the pupil—the central aperture that acts as the eye's adjustable aperture.^[5] The crystalline lens, positioned immediately posterior to the pupil and suspended by zonular fibers, provides the remaining one-third of the eye's refractive power and enables accommodation by altering its shape to fine-tune focus for varying distances.^[6] The vitreous humor, a gel-like substance filling the space between the lens and the retina, transmits light with minimal distortion due to its high water content and uniform refractive index.^[5] At the posterior aspect of the eye, the retina—a thin, light-sensitive neural layer—lines the inner surface of the vitreous chamber and contains photoreceptors (rods and cones) that convert focused light into electrical signals for transmission to the brain via the optic nerve.^[6] In a normal emmetropic eye, parallel light rays from distant objects enter through the cornea, are further converged by the lens, pass through the vitreous, and form a sharp image precisely on the retina's fovea centralis, the region of highest visual acuity.^[5] The refractive power of the eye is fundamentally determined by the axial length—the anteroposterior dimension of the eyeball, typically around 24 mm in adults—and the curvature of the cornea, which typically measures about 7.8 mm in radius and provides a fixed refractive contribution of approximately 43 diopters.^[6]^[7]^[8] These parameters ensure that light rays converge at the retinal plane without deviation, establishing the baseline for emmetropia.^[5]

Mechanism of refraction

Refraction in the human eye begins when light rays from an object enter the eye through the transparent cornea, the outermost layer of the eyeball, which accounts for approximately two-thirds of the eye's total refractive power of about 60 diopters (D), or roughly 43 D from the cornea alone.^[9]^[10]^[7] As light passes from air (refractive index n \approx 1) into the cornea (refractive index n \approx 1.376), it bends toward the normal due to the change in medium, following Snell's law: n_1 \sin \theta_1 = n_2 \sin \theta_2, where \theta_1 and \theta_2 are the angles of incidence and refraction, respectively.^[11]^[12] This initial bending converges the rays significantly. The light then traverses the aqueous humor (refractive index n \approx 1.336), where a smaller refraction occurs at the cornea-aqueous interface due to the closer refractive indices.^[9] Next, the rays reach the crystalline lens, located behind the iris, which contributes the remaining one-third of the refractive power, approximately 20 D in its relaxed state (refractive index n \approx 1.42).^[9]^[7] Refraction at the aqueous-lens interface further bends the light according to Snell's law, with the lens's higher refractive index causing additional convergence.^[12] In an emmetropic eye—characterized by normal vision—parallel light rays from distant objects focus precisely on the retina without requiring any accommodative effort from the lens, ensuring sharp imagery.^[13]^[14] For near vision, the process of accommodation adjusts the lens's shape: contraction of the ciliary muscle relaxes the zonular fibers, allowing the lens to become more convex and increase its refractive power by up to 10-12 D, thereby focusing divergent rays from closer objects onto the retina.^[15] This dynamic adjustment, enabled by the anatomical interplay of the ciliary muscle, zonules, and lens, maintains clear vision across varying distances.^[15]

Types of Refractive Errors

Myopia

Myopia, commonly known as nearsightedness, is a refractive error in which distant objects appear blurry because their images focus in front of the retina rather than on it, while near vision remains relatively clear. This occurs due to either excessive axial length of the eyeball (axial myopia) or increased refractive power of the optical components, such as the cornea or lens (refractive myopia). In axial myopia, the most common form, the eyeball is elongated, causing light rays from distant sources to converge prematurely before reaching the retina. Myopia is classified into subtypes based on severity and underlying pathology. Simple myopia, often referred to as school myopia or physiologic myopia, typically results from axial elongation and affects a large proportion of the population, with progression often stabilizing in early adulthood. Pathological myopia, also called degenerative or high myopia (generally defined as -6.00 diopters or more), involves more pronounced axial elongation that can lead to structural changes like posterior staphyloma, a localized outpouching of the sclera, increasing the risk of severe complications. Correction of myopia involves the use of diverging (concave) lenses, which spread out incoming light rays so that they focus properly on the retina. In an optical diagram, parallel light rays from a distant object enter the eye undeflected in emmetropia but converge in front of the retina in an uncorrected myopic eye; a diverging lens placed before the eye causes these rays to diverge slightly, shifting the focal point onto the retina. This principle applies to spectacles, contact lenses, or refractive surgeries like LASIK, which reshape the cornea to achieve a similar effect. The degree of myopia is measured in diopters (D), with negative values indicating the lens power required for correction; for example, -2.00 D signifies mild myopia, while -10.00 D or greater indicates high myopia. High myopia is associated with elevated risks of ocular complications, including retinal detachment due to traction on the elongated retina and open-angle glaucoma from altered optic nerve structure and vascular changes. These risks underscore the importance of monitoring in severe cases, as pathological changes can lead to irreversible vision loss. Genetic and environmental factors contribute to myopia development, but their detailed interplay is explored elsewhere.

Hyperopia

Hyperopia, also known as farsightedness or hypermetropia, is a refractive error in which parallel light rays from distant objects focus behind the neurosensory retina when the eye is at rest, due to insufficient converging power of the ocular media.^[16] This results in blurred near vision, while distance vision may remain relatively clear, particularly in mild cases where the eye's natural focusing mechanism compensates.^[17] The condition arises from either a shorter-than-normal axial length of the eyeball or reduced refractive power of the cornea and lens, leading to an overall underpowered optical system.^[18] Hyperopia is classified into two primary subtypes: axial and refractive. Axial hyperopia occurs when the anterior-posterior length of the eyeball is shortened, with each 1 mm reduction in axial length producing approximately 3 diopters of hyperopia.^[16] In contrast, refractive hyperopia stems from a flattened curvature of the cornea or lens (or both), where a 1 mm increase in the radius of curvature generates about 6 diopters of the error.^[16] These subtypes determine the degree to which the eye can naturally adjust, but both contribute to the focal point shifting posteriorly. In younger individuals, the ciliary muscle enables accommodation by increasing the curvature and converging power of the crystalline lens, often fully compensating for mild to moderate hyperopia and allowing clear vision at all distances without symptoms.^[17] This constant accommodative effort, however, can strain the visual system, leading to symptoms such as eye fatigue (asthenopia), headaches, and inward eye deviation (esotropia) during prolonged near work.^[18] Over time, this chronic demand accelerates the onset of presbyopia, as the lens loses elasticity earlier than in emmetropic eyes.^[16] Optically, hyperopia can be visualized as parallel incoming rays converging to a point behind the retina in the unaccommodated eye; correction requires a positive (convex) lens that adds converging power to shift the image plane forward onto the retina.^[18] The magnitude of hyperopia is measured in positive diopters (D), with low hyperopia defined as +2.00 D or less, moderate as +2.25 to +5.00 D, and high as greater than +5.25 D, reflecting the lens power needed for emmetropia.^[18] Uncorrected, severe cases blur vision across distances, potentially contributing to amblyopia if the refractive imbalance affects binocular development.^[16]

Astigmatism

Astigmatism is a type of refractive error characterized by unequal refractive power in different meridians of the eye, causing light rays to focus not at a single point on the retina but along two perpendicular focal lines.^[19] This irregularity results from the asymmetric curvature of the cornea or lens, leading to blurred or distorted vision at all distances.^[20] Astigmatism is classified into several types based on its location and regularity. Corneal astigmatism arises from uneven curvature of the cornea and can be regular, where the principal meridians are perpendicular and the curvature is symmetric around the optical axis, or irregular, which involves asymmetric or non-perpendicular meridians often due to trauma, disease, or surgery.^[19] Lenticular astigmatism, in contrast, originates from irregularities in the crystalline lens and is subdivided into curvatural (abnormal lens surface curvature), positional (lens tilt or displacement), and index (variations in the lens's refractive index).^[19] Regular corneal astigmatism is further categorized by axis orientation, such as with-the-rule (steep meridian near vertical, around 90 degrees) or against-the-rule (steep meridian near horizontal, around 180 degrees).^[20] Optically, astigmatism produces a configuration known as Sturm's conoid, where incoming parallel light rays are refracted by the toric (asymmetric) surface of the cornea or lens into two focal lines perpendicular to the principal meridians, rather than converging to a point focus.^[21] The interval between these focal lines, called the interval of Sturm, determines the degree of blur, with the retina typically lying within this conoid, resulting in a circle of least confusion where vision is sharpest but still suboptimal.^[19] This meridional variation in refractive power distinguishes astigmatism's blur pattern—often described as elongated or shadowed images—from the uniform defocus seen in pure myopia or hyperopia.^[20] The magnitude and orientation of astigmatism are measured in diopters (D) for power difference between meridians and degrees (0° to 180°) for the axis, indicating the direction of the steepest meridian relative to the horizontal.^[22] For example, a prescription might specify +1.00 D cylinder at 90° axis for with-the-rule astigmatism.^[19] Astigmatism frequently coexists with myopia or hyperopia, compounding the refractive error, but its distinct pattern of meridional blur requires specific correction using cylindrical lenses oriented along the principal axes to neutralize the irregularity.^[20]

Presbyopia

Presbyopia is an age-related refractive condition characterized by the gradual loss of the eye's accommodative ability, resulting in reduced capacity to focus on near objects due to hardening of the crystalline lens and weakening of the ciliary muscle. This condition typically begins to manifest in the early to mid-40s, affecting nearly all individuals by age 60, as the lens loses its elasticity through protein cross-linking and nuclear compaction, limiting its ability to change shape for near vision.^[23]^[24]^[25] The pathophysiology involves a progressive decrease in lens elasticity, with zonal changes such as sclerosis of the lens nucleus and reduced responsiveness to ciliary muscle contraction, which normally adjusts zonular tension to alter lens curvature. Although the ciliary muscle retains some function, the stiffened lens fails to accommodate adequately, leading to a decline in the amplitude of accommodation from approximately 7-10 diopters in young adulthood to near zero by age 60. Environmental factors, such as prolonged near work, may accelerate this process, though age remains the primary driver.^[23]^[24] Progression occurs in stages, starting mildly around ages 40-45 with a near add of +0.75 to +1.25 diopters, where individuals first notice difficulty reading small print in dim light or after prolonged near tasks. By ages 46-55, moderate progression requires +1.50 to +2.25 diopters, with symptoms including persistent blurred near vision, the need to hold objects at arm's length, eye strain, headaches, and fatigue during close work. In advanced stages after age 55, adds exceed +2.50 diopters, resulting in minimal residual accommodation and severe near vision impairment without correction. These symptoms primarily affect reading and fine tasks, distinguishing presbyopia from other refractive errors.^[23]^[25] Unlike hyperopia, which is an inherent refractive mismatch due to a shorter axial length or reduced corneal curvature requiring constant accommodation for both distance and near vision from a younger age, presbyopia represents an acquired failure of accommodative amplitude superimposed on any preexisting refraction. In emmetropic or myopic eyes, presbyopia solely impairs near focus, whereas in uncorrected hyperopes, it exacerbates preexisting farsightedness by eliminating compensatory mechanisms.^[23]^[24]^[16] Correction for presbyopia relies on bifocal or progressive addition lenses, which provide a plus power segment over the distance correction to restore near focus without altering far vision. Bifocals feature a distinct horizontal line separating the upper distance portion from the lower near segment, offering clear vision at two focal points but potentially causing image jump and limited intermediate range. Progressive lenses, in contrast, employ a gradual vertical increase in plus power from the top (distance) to the bottom (near), enabling seamless vision across all distances without visible lines, though adaptation may involve peripheral distortion. These principles aim to mimic lost accommodation by distributing refractive power spatially across the lens.^[23]^[24]^[25]

Causes and Risk Factors

Genetic factors

Refractive errors, particularly myopia, exhibit strong hereditary components, with twin studies consistently estimating heritability at 80-90%.^[26] These estimates derive from comparisons of monozygotic and dizygotic twins, highlighting the predominant role of genetic factors in refractive development over shared environmental influences.^[27] Specific genes have been implicated in myopia susceptibility, including PAX6, which influences ocular development and shows associations with high myopia through polymorphisms like rs644242.^[28] Similarly, SIX6 variants contribute to refractive error risk by affecting eye and optic disc morphology.^[29] Beyond individual genes, polygenic risk scores—aggregating multiple genetic loci—effectively predict myopia susceptibility, with scores explaining up to 8-10% of phenotypic variance in refractive error.^[30] Familial aggregation of high myopia often follows an autosomal dominant inheritance pattern, as observed in multigenerational pedigrees where affected individuals transmit the trait to approximately half of offspring.^[31] This mode is supported by linkage analyses mapping loci such as MYP2 on chromosome 18q.^[32] Ethnic variations in refractive error prevalence are partly attributable to genetic differences; for instance, East Asian populations exhibit higher myopia rates, linked to ancestry-specific alleles identified in genome-wide association studies.^[33] Gene-environment interactions modulate refractive error expression, where genetic predispositions may amplify susceptibility to developmental triggers, though detailed mechanisms remain under investigation.^[34] Heritability is also significant for other refractive errors. Hyperopia shows strong genetic influences, with loci such as NNO1 on chromosome 11p linked to high hyperopia through autosomal dominant inheritance.^[35] Astigmatism has moderate heritability estimates of 30-60%, primarily due to genes affecting corneal curvature and shape.^[36] For presbyopia, genetic factors contribute to variations in the age of onset, though aging remains the primary driver.^[37]

Environmental factors

Prolonged engagement in near work activities, such as reading and digital screen use, has been consistently linked to an increased risk of myopia development, particularly in children and adolescents. Meta-analyses indicate that individuals exposed to higher levels of near work exhibit odds ratios for myopia ranging from 1.26 to 2.24 compared to those with lower exposure, with dose-response relationships showing a 21% increase in odds per additional hour of daily screen time.^[38]^[39]^[40] Educational demands that intensify near work, including extended study hours, further amplify this risk, contributing to earlier onset and faster progression of refractive errors in school-aged populations.^[41] In contrast, increased time spent outdoors exerts a protective effect against myopia, with systematic reviews demonstrating reduced incidence and slower progression associated with at least 2 hours of daily outdoor exposure. The underlying mechanism is hypothesized to involve bright natural light stimulating retinal dopamine release, which inhibits axial elongation of the eye.^[42]^[43] This environmental factor is modifiable and has been shown to lower myopia odds by up to 50% in intervention studies, independent of near work levels.^[44] Nutritional deficiencies also play a role in refractive error susceptibility, with low serum levels of vitamin D associated with longer axial length and higher myopia risk in young children. Similarly, inadequate omega-3 fatty acid intake correlates with elevated myopia odds, as higher dietary consumption of these nutrients has been linked to a 20-30% reduction in risk through potential anti-inflammatory effects on ocular tissues.^[45]^[46] These associations highlight the importance of balanced nutrition in mitigating environmental contributions to refractive errors.^[47] Urbanization and socioeconomic status influence refractive error onset, with urban dwellers facing 1.5-2 times higher myopia prevalence due to reduced green spaces, limited outdoor access, and intensified educational pressures. Low socioeconomic environments exacerbate this through barriers to early detection and nutritional adequacy, accelerating myopia progression in affected children.^[48]^[49] The COVID-19 pandemic from 2020 onward intensified these environmental risks, as global lockdowns led to a surge in screen time—often exceeding 4-6 hours daily—and diminished outdoor activities, resulting in myopia prevalence tripling in some pediatric cohorts. Studies post-2020 report accelerated refractive error progression rates of 0.5-1.0 diopters annually during confinement periods, underscoring the rapid impact of altered lifestyles.^[50]^[38]^[51] These environmental factors are most prominent for myopia. For hyperopia and astigmatism, influences are subtler, with developmental factors like prematurity potentially contributing to astigmatism. Presbyopia is predominantly age-related, but environmental elements such as UV exposure, smoking, or medications may hasten lens hardening and symptom onset.^[23]

Epidemiology

Global prevalence

Uncorrected refractive errors cause vision impairment in approximately 1 billion people worldwide.^[52] According to the World Health Organization (WHO), at least 2.2 billion individuals have some form of vision impairment, of which uncorrected refractive errors account for the majority of preventable cases. These figures encompass all major types of refractive errors, including myopia, hyperopia, astigmatism, and presbyopia. Uncorrected refractive errors are a leading cause, contributing to over 80 million cases of moderate to severe vision impairment globally as of 2020 estimates.^[53] For presbyopia, an estimated 419 million people aged 50 and older had near vision impairment due to uncorrected presbyopia in 2020.^[53] Myopia, or nearsightedness, is the most prevalent form, affecting about 30-34% of the global population in 2020.^[54] Prevalence is markedly higher in urban East Asia, where rates reach 80-90% among young adults in countries such as South Korea, Taiwan, and Singapore.^[55] Projections from meta-analyses suggest that myopia alone could impact nearly 4.8-5 billion people by 2050, representing about 50% of the world's population.^[56] Hyperopia and astigmatism show lower but notable rates, particularly in children, with hyperopia affecting 4-6% and astigmatism 10-15% based on systematic reviews of pediatric populations.^[57] Regional disparities highlight elevated myopia rates in developed nations and urban settings, driven by factors such as prolonged near work in education systems.^[58] For instance, East and Southeast Asia report the highest burdens, with population prevalence exceeding 50% in some areas, while lower rates persist in rural and less industrialized regions.^[59] These patterns underscore the need for targeted interventions, as uncorrected refractive errors remain the principal cause of vision impairment worldwide.^[52]

Trends and demographics

The prevalence of myopia has been rising globally, often described as an epidemic, with historical data indicating an approximate 0.3% annual increase in prevalence over the past century in certain populations, such as a 2.5-fold rise from 22% to 56% between 1900 and 2000 in Dutch cohorts.^[60] This trend is strongly linked to urbanization, as urban living environments correlate with higher myopia rates due to factors like reduced outdoor time and increased near work, with studies showing a 32.1% increase in myopia prevalence over two years in highly urbanized groups from 2021 to 2023.^[48] Projections suggest continued escalation, with high myopia prevalence among children in urban China potentially reaching 18.8% by 2050 if current patterns persist.^[61] Age patterns in refractive errors exhibit distinct distributions: myopia, hyperopia, and astigmatism typically onset in childhood or adolescence, with myopia peaking around age 27 and hyperopia being most common in young children under 1 year (average +1.79 D).^[62] In contrast, presbyopia universally affects individuals after age 40 due to lens elasticity loss, impacting near vision and occurring in most people over 35.^[63] Gender differences show a slight predominance of myopia in males in older generations (32.3% vs. 29.3% in those born 1887–1960), though recent shifts indicate higher rates in females among youth, with 72.3% prevalence in adolescent girls compared to 70.5% in boys.^[64]^[65] Socioeconomic factors contribute to variations, with higher refractive error rates, particularly myopia, observed in higher-income groups due to increased near work from education and professional demands; for instance, high education and management occupations are associated with 45.7% myopia prevalence in men and high income with elevated rates in women.^[66]^[67] As of 2025, post-COVID-19 analyses reveal lasting effects from increased screen time on youth, with uncorrected myopia prevalence tripling from 3.7% to 12.6% during lockdowns and each additional hour of daily screen exposure raising myopia odds by 21%, contributing to accelerated progression in children.^[50]^[68]

Diagnosis

Symptoms and presentation

Refractive errors manifest primarily through disturbances in visual clarity and associated discomfort, varying by type and severity. Common patient-reported symptoms include blurred vision at specific distances, eye strain (asthenopia), headaches, and difficulty with tasks requiring precise focus. These signs arise when light is not properly focused on the retina, leading to compensatory behaviors like squinting.^[1] In myopia (nearsightedness), individuals typically report blurred vision for distant objects, such as difficulty reading road signs or recognizing faces from afar. Squinting is a frequent observable behavior to temporarily sharpen focus.^[69] Hyperopia (farsightedness) often presents with blurred near vision, though distant objects may appear clear. Symptoms include eye strain, burning or aching around the eyes, and headaches, particularly after prolonged close work like reading or using a computer, due to excessive accommodative effort. In younger individuals, mild hyperopia may remain asymptomatic as the eye's natural accommodation compensates effectively.^[70]^[16] Astigmatism causes blurred or distorted vision at all distances, often described as whirling or shadowy images. Associated symptoms encompass eyestrain, headaches, and discomfort, with squinting and challenges in low-light conditions like night vision being common.^[71] Presbyopia, an age-related refractive error, leads to gradual loss of near focus, with symptoms including the need to hold reading material at arm's length for clarity and blurred vision at normal reading distances. Eyestrain and headaches worsen after close tasks, often prompting the use of bifocals or reading glasses.^[25] Mild refractive errors across types can be asymptomatic, especially in children or young adults where accommodation masks deficits, though regular eye exams are essential for detection. In children, refractive errors may present through behavioral signs such as poor school performance, excessive eye rubbing or blinking, sitting unusually close to the television or books, or tilting the head to one side to improve vision, even if the child does not complain of symptoms.^[1]^[72]

Examination techniques

Visual acuity testing serves as the initial step in evaluating refractive errors, measuring the clarity of vision to identify potential deficits that may indicate uncorrected or undercorrected refraction. The Snellen chart, developed in 1862, remains a widely used tool where patients read letters of decreasing size at a standard distance of 6 meters (20 feet), with acuity expressed as a fraction such as 20/20 for normal vision.^[73] For greater precision and sensitivity, especially in research and clinical settings, the logMAR chart is preferred, as it uses a logarithmic scale where each line represents 0.1 log units, allowing for more accurate quantification of small changes in visual acuity.^[73] These tests are typically performed monocularly with the patient's current correction, if any, to establish a baseline for further refraction.^[74] Objective refraction provides an initial estimate of refractive error without relying on patient responses. Retinoscopy involves observing the reflex from the retina when a streak of light is projected into the eye using a retinoscope. The examiner neutralizes the reflex movement with trial lenses held before the eye, determining the spherical and cylindrical components of the refraction, making it particularly valuable for children, non-verbal patients, or those with unreliable subjective feedback.^[75] This technique involves working distance correction—typically subtracting 1.50 diopters for a 67 cm working distance—and assessing the reflex in multiple meridians to detect astigmatism.^[76] Autorefraction, using an automated instrument, measures the refractive error by analyzing the light reflected from the retina, providing a quick objective assessment suitable for most patients, though it may be less accurate in cases of media opacities or irregular astigmatism.^[74] Cycloplegic agents, such as tropicamide or cyclopentolate drops, are often instilled prior to objective refraction in younger patients to paralyze the ciliary muscle and relax accommodation, preventing pseudomyopia and ensuring accurate measurement of latent hyperopia.^[77] Instillation typically involves 1-2 drops, with refraction performed 20-30 minutes later, though effects can persist for hours.^[74] Subjective refraction refines the objective findings by using patient feedback to optimize lens power and achieve the best-corrected visual acuity. A phoropter, an instrument holding trial lenses, is positioned before the eyes, allowing rapid changes in spherical, cylindrical, and axis settings while the patient views an acuity chart.^[78] The process begins with fogging to relax accommodation, followed by duochrome testing and cross-cylinder refinement for astigmatism, ensuring reproducibility within 0.25 to 0.50 diopters.^[74] Alternatively, trial lenses in a frame offer a more natural view for patients with high refractive errors or discomfort in the phoropter, though the phoropter is standard for its efficiency in cooperative adults.^[79] For astigmatism, keratometry and corneal topography quantify corneal irregularity, which contributes significantly to refractive asymmetry. Keratometry measures the radius of curvature in principal meridians using a keratometer, projecting mires onto the cornea and calculating power in diopters, typically revealing with-the-rule astigmatism where the vertical meridian is steeper. Corneal topography extends this by mapping the entire anterior surface with Placido disc or Scheimpflug imaging, generating color-coded maps that display power distribution, axis orientation, and irregularity indices to differentiate regular from irregular astigmatism. These instruments are essential for preoperative planning in refractive surgery and contact lens fitting, with topography providing higher resolution for detecting subtle corneal warpage.^[74]

Screening

Screening methods

Screening for refractive errors in asymptomatic individuals aims to detect uncorrected vision problems early, particularly in children where timely intervention can prevent amblyopia and other complications. Instrument-based methods, such as photoscreening and autorefraction, are widely used for young children who may not cooperate with traditional tests. Photoscreening employs specialized cameras to capture images of the undilated eyes, analyzing light reflections from the retina to estimate refractive errors, media opacities, and misalignment without requiring active patient responses; it is effective for children as young as 6 months and is recommended by the American Academy of Pediatrics for use starting at 12 months in this age group.^[80]^[81] Handheld autorefractors complement this by providing objective measurements of refractive status through automated infrared light projection and analysis, offering quick estimates of sphere, cylinder, and axis in preverbal or nonverbal children.^[82] In school settings, vision charts like the Snellen or HOTV optotypes are standard for assessing visual acuity in children aged 3 years and older, identifying potential refractive errors if acuity falls below age-appropriate norms (e.g., 20/40 or better by age 4). The plus lens test, a near-point assessment using convex lenses (typically +1.50 to +2.25 diopters depending on age), helps detect latent hyperopia by observing accommodative responses, though its use varies and is not universally endorsed as a primary tool.^[83]^[84] Autorefraction devices, including tabletop and portable models, enable high-throughput screening in these environments by delivering rapid, non-cycloplegic refractive estimates, often integrated into protocols for grades K-12.^[85] The American Academy of Ophthalmology recommends vision screening at least every 1 to 2 years for school-aged children during health visits or school checks, with more frequent annual assessments in educational settings to monitor refractive changes during growth. For adults without risk factors, the AAO recommends comprehensive eye examinations starting with a baseline at age 40, followed by every 2-4 years for ages 40-54, every 1-3 years for ages 55-64, and every 1-2 years for age 65 and older, to detect emerging presbyopia or shifts in refractive error.^[86]^[87] These methods are non-invasive, requiring minimal cooperation, and support high-throughput application in population-based programs, with positive screens prompting referral for detailed diagnostic evaluation.^[88]

Guidelines and recommendations

The World Health Organization's Vision 2020: The Right to Sight initiative, launched in 1999, prioritizes the integration of refractive error screening into primary health care to combat uncorrected refractive errors, which are a leading cause of avoidable visual impairment globally.^[89] This approach aims to ensure equitable access to basic vision services, including refraction and provision of affordable spectacles, by embedding eye care within existing community health frameworks.^[90] Building on this, the subsequent SPECS 2030 initiative extends these efforts, advocating for people-centered refractive care that addresses barriers in low- and middle-income countries through strengthened primary care integration.^[91] For pediatric populations, the American Academy of Pediatrics (AAP) and the American Academy of Ophthalmology (AAO) recommend routine vision screening in infancy and early childhood to detect refractive errors that could lead to amblyopia or other developmental issues. Specifically, instrument-based screenings should occur during well-child visits starting at 12 months (e.g., at 12, 18, and 24 months) using methods like photoscreening or autorefraction, followed by assessments at preschool ages (typically 3-5 years) to evaluate visual acuity and alignment.^[80]^[87] These guidelines emphasize early detection to allow for timely intervention, as uncorrected refractive errors in infancy can impair visual development.^[92] In adults, the AAO advises a baseline comprehensive eye examination at age 40 for those without known risk factors, with subsequent screenings every 2-4 years for ages 40-54, every 1-3 years for ages 55-64, and every 1-2 years for age 65 and older to monitor changes in refractive error and detect associated conditions like presbyopia.^[86] This frequency may increase for individuals with diabetes, hypertension, or family history of eye disease, ensuring ongoing management of refractive needs.^[93] Evidence supports the cost-effectiveness of these early screening protocols, particularly in preventing amblyopia through prompt refractive correction, which reduces long-term visual impairment and associated healthcare costs.^[94] For instance, vision screening programs in primary care settings have demonstrated favorable cost per quality-adjusted life year gained, especially when targeting high-risk pediatric groups.^[95] As of 2025, updates from organizations like the WHO highlight the role of AI-assisted tools in refractive error screening, particularly in low-resource areas where traditional methods face logistical challenges.^[96] These innovations, such as portable AI-enabled autorefractors, improve detection accuracy and scalability, aligning with global goals for accessible eye care.^[97]

Management

Spectacles

Spectacles, also known as eyeglasses, represent the most common and non-invasive method for correcting refractive errors such as myopia, hyperopia, astigmatism, and presbyopia.^[98] They function by using lenses to bend light rays appropriately onto the retina, thereby improving visual acuity without altering the eye's structure.^[99] The invention of spectacles dates back to the late 13th century in northern Italy, where monks and scholars first developed convex lenses mounted in frames to aid reading for those with presbyopia.^[100] Various lens types address different refractive needs. Single-vision lenses provide correction for one focal distance, either for distance vision in cases of myopia or hyperopia, or for near vision in presbyopia.^[98] Bifocal lenses, invented by Benjamin Franklin in 1784, feature two distinct zones: the upper portion for distance vision and the lower for near tasks, making them suitable for presbyopia.^[98] Progressive lenses, also called multifocals, offer a seamless gradient of correction across three zones—distance at the top, intermediate in the middle, and near at the bottom—without visible lines, providing a more natural field of view for presbyopia but potentially causing peripheral distortion in about 10% of users.^[98] Lens materials are selected based on durability, weight, and optical quality. Polycarbonate lenses are highly impact-resistant and lightweight, making them ideal for children, sports activities, and safety applications due to their ability to withstand high-velocity impacts without shattering.^[98] High-index plastic lenses, with a refractive index typically ranging from 1.60 to 1.74, allow for thinner profiles compared to standard plastic or glass, which is particularly beneficial for individuals with strong prescriptions to minimize lens thickness and the "coke-bottle" appearance.^[101] Frame selection plays a crucial role in ensuring comfort and effective use. Proper fit involves frames that rest securely on the nose bridge and ears without slipping or pinching, often adjustable in metal types like titanium for personalized alignment.^[102] Lightweight materials such as titanium, stainless steel, or zyl plastic reduce fatigue during prolonged wear, while aesthetics influence choice through diverse styles, colors, and hypoallergenic options to match personal preferences and face shapes.^[102] Compliance with spectacle wear, especially among children and adolescents, remains a significant challenge, with studies reporting rates as low as 40% overall and even lower in urban or older youth due to factors like peer stigma, aesthetic concerns, and misconceptions about dependency.^[103] Interventions such as involving children in frame selection and educating families can improve adherence, ensuring consistent correction of refractive errors to support visual development.^[104]

Contact lenses

Contact lenses are optical devices worn directly on the cornea to correct refractive errors such as myopia, hyperopia, astigmatism, and presbyopia by altering the way light rays focus on the retina.^[105] Unlike spectacles, they provide a wider field of unobstructed vision and are particularly beneficial for active lifestyles or those requiring aesthetic correction without frames.^[106] These lenses must be precisely fitted to ensure comfort, visual acuity, and ocular health, as improper use can lead to significant complications.^[107] The primary types of contact lenses for refractive error correction include soft lenses, rigid gas permeable (RGP) lenses, and specialized variants like toric lenses. Soft lenses, made from hydrogel or silicone hydrogel materials, are flexible and comfortable due to their high water content (typically 30-80%), allowing them to conform to the eye's shape.^[105] Hydrogel lenses prioritize hydration but have lower oxygen permeability, while silicone hydrogel lenses incorporate silicone for enhanced oxygen transmission (Dk values often exceeding 100), reducing the risk of corneal hypoxia during wear.^[108] RGP lenses, constructed from rigid, oxygen-permeable plastics, offer sharper vision for irregular corneas or high astigmatism and last longer but may require an adaptation period due to their firmness.^[105] Toric soft or RGP lenses are designed specifically for astigmatism, featuring weighted bottoms or prism ballasts to maintain stable orientation on the eye and correct asymmetric corneal curvature.^[105] The fitting process begins with a comprehensive eye examination to measure corneal curvature (keratometry), pupil size, and tear film quality, followed by selecting parameters like base curve (the radius of the lens's back surface, typically 8.3-9.0 mm to match corneal steepness) and overall diameter (13.8-14.5 mm for soft lenses to ensure full coverage without slippage).^[109] Trial lenses are then inserted and evaluated for movement, centration, and visual performance using fluorescein dye to assess fit; adjustments are made iteratively until optimal alignment is achieved, often requiring multiple visits.^[109] Wear schedules vary to balance convenience and safety, with daily disposable lenses intended for single-day use and discarded nightly to minimize infection risk through reduced handling and cleaning.^[107] Extended-wear lenses, approved for overnight use up to 7-30 days depending on the material (e.g., high-oxygen silicone hydrogel), allow continuous wear but carry higher risks and require weekly removal for disinfection.^[110] Compliance with replacement schedules—biweekly, monthly, or yearly for reusable lenses—is essential to prevent deposit buildup.^[107] Complications from contact lens wear primarily involve infections, with microbial keratitis being the most severe, occurring at a rate of approximately 2-5 cases per 10,000 wearers annually and potentially leading to corneal scarring or vision loss if untreated.^[111] Risk factors include overnight wear, poor hygiene, and lens overwear, which can increase incidence by up to 10-15 times compared to daily wear.^[112] Other issues include giant papillary conjunctivitis from protein deposits and corneal neovascularization due to chronic hypoxia.^[113] In special applications, orthokeratology (ortho-k) uses rigid gas-permeable lenses worn overnight to temporarily flatten the central cornea via hydraulic compression, thereby reducing myopia progression in children by 30-50% over two years through altered peripheral defocus.^[114] This non-surgical method provides spectacle-free daytime vision but requires diligent monitoring to avoid infection risks associated with extended overnight use.^[114]

Refractive surgery

Refractive surgery encompasses a range of procedures aimed at permanently reshaping the eye's optical structures to correct refractive errors such as myopia, hyperopia, and astigmatism. These interventions typically target the cornea or lens, altering how light is focused onto the retina to reduce or eliminate dependence on corrective eyewear. Unlike temporary aids, refractive surgeries seek durable vision improvement, though outcomes vary based on individual anatomy and procedure type.^[115] Laser-assisted in situ keratomileusis (LASIK) is one of the most common corneal refractive procedures, involving the creation of a thin corneal flap using a femtosecond laser, followed by excimer laser ablation to reshape the underlying stroma. The flap is then repositioned, allowing rapid healing and minimal discomfort. Clinical studies demonstrate high efficacy, with approximately 95% of patients achieving uncorrected visual acuity of 20/40 or better one year post-procedure.^[116]^[117] Photorefractive keratectomy (PRK) and small incision lenticule extraction (SMILE) serve as surface ablation alternatives to LASIK, suitable for patients with thinner corneas or those at risk for flap-related issues. In PRK, the corneal epithelium is removed, and an excimer laser directly ablates the surface to adjust curvature, followed by a protective contact lens during epithelial regrowth. SMILE, a flapless technique, employs a femtosecond laser to create and extract a lenticule within the cornea through a small incision, preserving more corneal nerves and potentially reducing postoperative dry eye. Both methods yield comparable visual outcomes to LASIK, with over 90% of patients reaching 20/40 vision, though PRK may involve a longer recovery period.^[118]^[119] For high refractive errors or cases unsuitable for corneal procedures, lens-based surgeries such as phakic intraocular lens (IOL) implantation offer an alternative by placing an artificial lens in front of the natural one, without removing the crystalline lens. These are particularly effective for severe myopia exceeding -8 diopters or post-cataract scenarios where refractive adjustment is needed alongside lens replacement. Pseudophakic IOLs, used after cataract extraction, can simultaneously address residual errors. Outcomes show significant refractive correction, with most patients achieving within 1 diopter of emmetropia.^[120]^[121] Ideal candidates for refractive surgery are typically over 18 years old with stable refraction for at least one year, ensuring the procedure addresses a consistent error rather than ongoing changes. Comprehensive preoperative evaluation, including corneal topography and tear film assessment, confirms suitability and minimizes risks.^[122] Potential risks include temporary dry eye due to nerve disruption, affecting up to 30% of patients in the first six months, and visual disturbances such as halos or glare around lights, particularly at night. These symptoms often resolve but can persist in rare cases, emphasizing the need for informed consent.^[123]^[124] By 2025, advancements in femtosecond laser technology, such as the VisuMax 800 system, have enhanced precision with faster pulse rates and improved docking, reducing procedure time and intraoperative discomfort while supporting procedures like SMILE and customized LASIK profiles. These innovations contribute to better safety profiles and broader applicability for complex refractive cases.^[125]

Pharmacological interventions

Pharmacological interventions for refractive errors primarily target myopia progression, as it is the most common and progressive form, using agents that modulate ocular growth or facilitate precise diagnosis. These approaches are non-invasive and often temporary, contrasting with permanent corrections like surgery. Atropine eye drops, administered in concentrations ranging from 0.01% to 1%, represent the most established option for slowing myopia advancement in children through muscarinic receptor inhibition, which influences scleral remodeling and choroidal blood flow beyond mere accommodation paralysis.^[126] In clinical trials, 1% atropine achieved a 50-60% reduction in myopia progression over two years compared to placebo, while lower doses like 0.01% provided about 50% reduction with sustained effects over five years and minimal rebound upon cessation.^[126] The ATOM2 study, involving 400 children, demonstrated that 0.01% atropine slowed spherical equivalent progression to -1.38 ± 0.98 D and axial elongation to 0.75 ± 0.48 mm over five years, outperforming higher concentrations (0.1% and 0.5%) in long-term efficacy due to lower rebound rates.^[126] For presbyopia, pharmacological treatments include eye drops that temporarily improve near vision by constricting the pupil to create a pinhole effect, enhancing depth of focus. Pilocarpine hydrochloride 1.25% ophthalmic solution (Vuity), approved by the FDA in 2021, is instilled once daily and provides functional near vision improvement for approximately 6 hours in presbyopic adults, with studies showing 3 additional lines of near visual acuity in about 73% of users under low light. As of 2025, additional options include pilocarpine 0.4% (Qlosi, launched early 2025) for preservative-free, once-daily use with fewer dimming effects, and aceclidine 1.44% (VIZZ, approved July 2025), which offers similar efficacy with potentially less headache. Common side effects across these include temporary headache, eye redness, and reduced vision in dim light, affecting 10-30% of users, but they are generally well-tolerated without systemic risks.^[127]^[128]^[129] Cycloplegic agents, such as atropine, cyclopentolate, or tropicamide, are employed diagnostically to ensure accurate refraction in children by paralyzing accommodation, which can otherwise mask hyperopia or underestimate myopia. This is particularly crucial in pediatric populations where latent refractive errors may lead to overprescribing or missed interventions. Guidelines from the World Health Organization recommend cycloplegic refraction for reliable myopia diagnosis and prescription confirmation, especially in younger children, as non-cycloplegic methods risk inaccuracies up to 1.00 D.^[130] For instance, atropine or cyclopentolate provides full cycloplegia within 30-60 minutes, enabling precise measurement of true refractive status without accommodative interference.^[130] Emerging pharmacological options include 7-methylxanthine (7-MX), an oral adenosine antagonist that modulates scleral hypoxia and collagen synthesis to potentially retard axial elongation in myopia. Experimental as of 2025 and licensed only in Denmark since 2009, 7-MX showed modest efficacy in a pilot trial of 68 myopic children, reducing axial growth by 0.03 mm and progression by 0.07 D over one year, with stronger effects (up to 50% reduction in form-deprivation models) in animal studies.^[131] Clinical adoption remains limited due to small effect sizes and need for longer-term data.^[132] Common side effects of these agents, particularly atropine, include photophobia from pupil dilation and near vision blur due to reduced accommodation, though low-dose (0.01%) formulations minimize these to negligible levels (e.g., 0.8 mm dilation and 2-3 D loss). Higher concentrations (0.5-1%) exacerbate symptoms, leading to discontinuation in up to 68% of cases post-trial. No systemic effects are typically reported with topical use, but local irritation may occur.^[133]

Prevention

Lifestyle measures

Spending at least two hours outdoors daily has been shown to reduce the risk of myopia onset in children, with each additional hour of outdoor time associated with a 13% decrease in myopia risk.^[134] This protective effect is attributed to exposure to natural light, which may influence dopamine release in the retina and inhibit axial elongation of the eye.^[135] Studies, including school-based interventions, confirm that increasing outdoor activities during childhood lowers the incidence of new myopia cases and slows refractive error progression, particularly in non-myopic individuals.^[136] To mitigate strain from prolonged near work, which can contribute to refractive error development, the 20-20-20 rule is recommended: every 20 minutes, look at an object 20 feet away for at least 20 seconds.^[137] This practice relaxes the eye's focusing muscles, reduces accommodative spasm, and alleviates digital eye strain symptoms that exacerbate near-work-induced transient myopia.^[138] Compliance with this rule, especially during screen-based activities, helps prevent the cumulative visual fatigue linked to refractive changes.) A balanced diet rich in antioxidants supports overall lens health and may help mitigate oxidative stress associated with refractive errors. Nutrients such as vitamins C and E, along with lutein and zeaxanthin found in fruits, vegetables, and nuts, exhibit anti-inflammatory properties that counteract processes potentially contributing to myopia and astigmatism.^[139] Emerging evidence indicates that adequate intake of these antioxidants through diet promotes retinal protection and eye structure integrity, potentially reducing the severity of refractive conditions.^[140] Proper lighting during reading activities is essential to prevent eye strain and support refractive health; illumination levels around 500-1000 lux reduce the risk of myopia progression compared to dim environments below 459 lux.^[141] Maintaining an upright posture while reading, with materials held at arm's length, minimizes intraocular pressure increases and accommodative effort that could induce transient refractive shifts.^[141] These habits ensure even light distribution on the page, avoiding glare or shadows that strain the ciliary muscles.^[137] Ergonomic adjustments for digital devices further aid in preventing refractive error aggravation from near work. Position screens at or slightly below eye level, about 20-30 inches away, with the top of the monitor aligned to allow a 10-20 degree downward gaze; this setup, combined with relaxed shoulders and supported lower back, reduces neck strain and visual discomfort.) Use adjustable lighting to match ambient conditions, minimizing glare, and ensure feet are flat on the floor with wrists neutral to sustain comfortable viewing distances that lessen accommodative demand.^[137]

Emerging preventive strategies

Orthokeratology involves the overnight wear of rigid gas-permeable contact lenses that temporarily reshape the cornea to provide clear daytime vision without correction, and it has demonstrated efficacy in slowing myopia progression in children. A meta-analysis of randomized controlled trials found that orthokeratology reduced myopic progression by approximately 44% compared to single-vision spectacles, with similar benefits observed in both Asian and non-Asian cohorts. This effect is attributed to the peripheral defocus created by the corneal reshaping, which may influence emmetropization signals in the developing eye.^[142] Defocus incorporated multiple segments (DIMS) spectacles represent an advancement in optical interventions, featuring a central clear zone for distance vision surrounded by segments that induce myopic defocus in the periphery to promote axial length stabilization. In a two-year randomized clinical trial involving children aged 8-13 years, DIMS lenses reduced myopia progression by 52% and axial elongation by 62% relative to progressive addition lenses. Follow-up studies over three years confirmed sustained efficacy, with continued slowing of progression even after switching from single-vision lenses, highlighting their role in long-term myopia control.^[143]^[144] Emerging public health initiatives, particularly in regions with high myopia prevalence, focus on school-based interventions to reduce near-work demands, such as China's "Double Reduction" policy implemented in 2021, which limits homework volume and after-school tutoring to curb educational pressures. A population-based study in eastern China showed that one year post-policy, the mean myopic shift among school-aged children decreased significantly, with the proportion of myopia stabilizing or improving in affected groups. These interventions aim to increase outdoor time and decrease prolonged close-focus activities, aligning with evidence that reduced near-work correlates with lower myopia incidence.^[145] Gene therapy approaches targeting genetic factors influencing refractive error remain in preclinical stages as of 2025, with research focusing on genes that regulate axial eye length to prevent myopia onset. For instance, in murine models of posterior microphthalmos caused by MFRP mutations—which lead to shortened axial length and hyperopic refractive errors—adeno-associated virus-mediated gene therapy restored MFRP expression and corrected axial elongation by an average of 0.1 mm, demonstrating potential for modulating refractive development. Such preclinical trials underscore the promise of genetic interventions for high-risk populations, though human applications require further safety and efficacy validation.^[146] Long-term extensions of the Correction of Myopia Evaluation Trial (COMET) provide insights into natural progression patterns and inform preventive strategies by identifying stabilization factors. Over 13 years of follow-up in the original cohort, myopia stabilized in most participants by late adolescence, with younger age at onset, higher baseline myopia, and parental myopia strongly predicting prolonged progression. These findings support emerging preventive models that emphasize early intervention before age 10, integrating optical and behavioral measures to mimic emmetropizing influences observed in longitudinal data.^[147]^[148]

Societal Impact

Disease burden

Uncorrected refractive error (URE) remains the leading cause of visual impairment worldwide, particularly among working-age adults, with an estimated 157 million people experiencing moderate to severe vision impairment and 3.7 million cases of blindness attributable to it as of 2020. This burden disproportionately affects low- and middle-income countries, where 90% of the 1.1 billion individuals living with vision impairment reside, and approximately 1 billion cases in these regions stem from uncorrected refractive issues, including 544 million with distance vision problems. Recent 2025 assessments indicate ongoing challenges, with global effective refractive error coverage at 65.8% in 2023, highlighting persistent gaps in access to correction despite progress toward targets like those set in the post-VISION 2020 era, such as restoring vision for 255 million people by 2030.^[149]^[150] URE significantly contributes to productivity losses through educational setbacks and workplace hazards. In children, uncorrected errors hinder learning, with affected individuals acquiring roughly half the educational gains of their peers, potentially resulting in 3.3 million lost school years globally by 2030 without intervention. Among adults, particularly in occupational settings like driving, URE elevates accident risks—for instance, visual impairment is associated with a 46% higher risk of road traffic crashes overall, and a 2025 pilot study in India found 55.1% of truck drivers surveyed had compromised vision—leading to reduced employment rates, as those with moderate to severe impairment are 30% less likely to hold jobs.^[150]^[151]^[152] The condition also imposes substantial mental health burdens and long-term complications. Children with uncorrected refractive errors often experience diminished self-esteem and psychological well-being, with studies showing lower scores in quality-of-life domains related to emotional and social functioning. Additionally, 25% of individuals with vision impairment suffer from depression, a risk that vision correction could mitigate for up to 1.7 million cases by 2030. In childhood, uncorrected myopia or hyperopia can lead to amblyopia, the most common cause of vision loss in children, affecting development if not addressed early.^[153]^[154]^[150]^[155]^[156]

Economic costs

Refractive errors impose significant direct costs on individuals through corrective measures such as spectacles and contact lenses, which typically range from $100 to $500 annually depending on prescription complexity, replacement frequency, and materials used. Refractive surgery, including procedures like LASIK, represents a higher one-time expense of $2,000 to $4,000 per eye, varying by technology, surgeon expertise, and location.^[157] These costs accumulate over lifetimes, particularly for progressive conditions like myopia, where ongoing optical corrections or surgical interventions are required to maintain visual acuity. Indirect costs from refractive errors are substantial, primarily manifesting as lost productivity due to uncorrected or undercorrected vision, estimated at $269 billion annually in international dollars based on 2007 global data, with uncorrected refractive error accounting for a large share of vision impairment cases.^[158] More recent assessments indicate that productivity losses from all vision impairment, of which refractive errors are a leading cause, reached $411 billion in 2020, equivalent to about 0.3% of global GDP.^[159] In high-prevalence regions, these losses can represent 0.2% to 1% of national GDP, underscoring the broader economic drag from reduced workforce efficiency and educational outcomes.^[160] In low-resource areas, where approximately 90% of individuals with refractive errors remain uncorrected due to limited access to eye care services and affordability barriers, these economic burdens are amplified, leading to higher rates of vision-related disability and sustained productivity deficits.^[161] Healthcare expenditures on refractive error management in such settings further strain limited budgets, often prioritizing other health needs over optical corrections. Earlier estimates from 2012 suggested that uncorrected myopia could cost high-burden countries like China 1-3% of GDP if refractive services do not expand; a 2023 study estimated total annual myopia costs in urban China at $26.3 billion (0.23% of GDP).^[162]

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The estimate for 2020 showed the population prevalence of myopia for these regions as 53.4 % and 51.6 % respectively, rising to 66.4 % and 65.3 % respectively ...
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a pooled analysis of Dutch population-based cohorts (1900–2000)
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Jan 27, 2025 · Here the prevalence of high myopia increased from 6.2% in 2020 to 10.0%, 14.4%, and 18.8% in 2030, 2040, and 2050, respectively (Fig. 3a).
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Myopia, hyperopia, astigmatism, and presbyopia are the four most common refractive errors. ... With an assumed onset age of 40 to 45 years, presbyopia is ...
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Gender issues in myopia: a changing paradigm in generations
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... myopia and several socioeconomic factors. There are many studies examining the distribution of refractive error and the risk factors for the refractive errors.
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Farsightedness (hyperopia). This occurs when the cornea is curved too little or the eye is shorter than usual. The effect is the opposite of nearsightedness.
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Many studies in ophthalmology have recorded visual acuity using a Snellen chart, and then the Snellen visual acuity is converted to logMAR value using a ...
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Sep 9, 2022 · This may be accomplished by using manifest (noncycloplegic) refraction with fogging or other techniques to minimize accommodation with care to ...
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Apr 22, 2020 · Retinoscopy provides an objective means for assessing refractive error. It is an indispensable test for pediatric patients, and is helpful in non- or preverbal ...
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Cycloplegics are drugs that paralyze the ciliary muscles and cause relaxation of accommodation. · The various cycloplegic agents are atropine sulfate, ...
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Subjective refraction is the assessment of refractive status by a combination of spherical and cylindrical lenses to determine the best-corrected visual acuity.
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Nov 3, 2023 · Photoscreening and screening with handheld autorefractors may be electively performed on children as young as 6 months, allowing earlier ...
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A. 2.25 convex lens power is appropriate to test ages 5 through 8 years; and a 1.75 convex lens should be used to test students over 8 years of age. Either + ...
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Refractive care provides excellent access to the population for screening of more serious eye problems, such as cataract and diabetes. Primary care screening by ...
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Uncorrected refractive error is the leading cause of vision impairment in child and adult populations. It is estimated that 2 out of 3 people in low-income ...
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Jun 14, 2023 · There are two main types of eyeglasses. Single-vision glasses have a lens designed to help you see either close up or far away. Multifocal ...
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### Summary of Eyeglass Frame Considerations
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Aug 11, 2021 · Dr. Sonia Yoo discusses prescribing contact lenses for refractive errors, monovision for correction of presbyopia in contact lens wearers, and bandage contact ...
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May 27, 2025 · Wearing daily disposable contact lenses for more than one day may cause eye discomfort or other complications.At A Glance · Contact Lens Wear Schedule · Special Contact Lens Types
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Aug 21, 2015 · The largest single risk factor for microbial keratitis is contact lens wear (3).
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Apr 23, 2023 · Orthokeratology, or ortho-k, is the use of specially designed and fitted contact lenses to temporarily reshape the cornea to improve vision.
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Feb 24, 2023 · Refractive surgery can correct refractive errors like nearsightedness, farsightedness, astigmatism, or presbyopia. Some of these surgeries ...
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May 18, 2018 · One-year clinical results of LASIK with the FS200 femtosecond laser and EX500 excimer laser showed high efficacy, predictability, stability and safety.
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Aug 25, 2023 · The phakic intraocular lens (IOLs) is a technology that expands the range of refractive surgery to cover higher degrees of myopia, hyperopia, and astigmatism.
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Jul 16, 2025 · Nearsightedness, also called myopia. In nearsightedness, your eyeball is slightly longer than typical or the cornea curves too sharply.
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Aug 9, 2024 · scratchiness, dryness and other symptoms of dry eye; glare; halos (rings) or starbursts around lights · double vision · decreased ability to see ...
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Dec 1, 2020 · Cycloplegic refraction is recommended before treatment and to confirm changes in prescription, especially in younger children, and is seen in ...
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7-Methylxanthine and Caffeine. Oral 7-methylxanthine (7-mx), a nonselective adenosine antagonist, has been licensed for myopia control in Denmark since 2009 ...
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Jun 30, 2022 · Conclusions: Increasing outdoor time reduced the risk of myopia onset and myopic shifts, especially in nonmyopic children. The protective effect ...
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... 20-20-20 rule to reduce eye strain. Innovations in this field include high-resolution screens, inbuilt antireflective coating, matte-finished glass, edge-to ...
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Emerging research suggests that maintaining a balanced diet is important due to the potential impact of certain nutrients on myopia development.4. Myopia Correction Methods... · 5. Effect Of Diet On The... · 5.2. Micronutrients
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Jul 2, 2025 · The findings suggest that having good illumination and an upright posture when reading, resting the eyes, adequate sleep, spending time ...
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Oct 31, 2025 · A two-year randomised clinical trial (RCT) demonstrated DIMS spectacle lenses reduced myopia progression by 52% and axial elongation by 62% in ...
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Aims To determine myopia progression in children who continued to wear the defocus incorporated multiple segments (DIMS) lenses or switched from single vision ( ...
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The model accounts for near vision refractive error. (presbyopia), distance vision refractive error and cataracts - which comprise 90% of all vision impairment.
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If your child has a refractive error that's not treated right away, they can develop amblyopia. Refractive errors in kids that lead to amblyopia include:.<|separator|>
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Sep 23, 2025 · estimated that, without the rapid development of refractive services in China, uncorrected myopia could cost the country 1–3% of its GDP due to ...