Errores de refracción

Refractive errors are the most common vision problem in the world. They occur when the shape of the eye does not bend (refract) incoming light correctly, so images focus in the wrong place and vision becomes blurry or distorted. The word refraction refers to the way light rays change direction when they pass from air into the eye. In a perfectly shaped eye, light from a distant object passes through the cornea (the clear front surface) and the crystalline lens (the focusing lens inside the eye) and comes to a sharp focus precisely on the retina—the light-sensitive layer at the back of the eye that converts the image into nerve signals sent to the brain. When the cornea is too curved, too flat, or irregularly shaped, or when the eyeball itself is too long or too short, the focal point lands in front of or behind the retina instead of directly on it, producing blurred vision.

Refractive error (ametropia) is an umbrella term covering four classic subtypes—myopia, hyperopia, astigmatism, and presbyopia—as well as clinically related conditions, including anisometropia (significantly unequal refractive error between the two eyes) and keratoconus (a progressive corneal shape disorder). Each type causes blurred vision through a different optical mechanism, and each requires its own correction approach. Unlike most eye diseases that involve inflammation, infection, or degeneration, refractive errors are fundamentally structural and optical—they reflect the geometry of the eye rather than damage to its tissue. This means they can be fully corrected with the right lenses, and in many cases can be permanently reduced or eliminated with surgery.

Refractive errors are extraordinarily common. More than 150 million Americans have a refractive error—many without realizing their vision could be substantially better with correction. Myopia (nearsightedness) alone affects approximately 42% of Americans aged 12 to 54, up from just 25% in the early 1970s. Presbyopia—age-related loss of near focus—affects virtually all adults by their mid-40s to mid-50s. Globally, approximately 2.6 billion people were living with myopia in 2020, and projections suggest this will rise to 4.9 billion—more than half the world’s population—by 2050 unless preventative action is taken. Uncorrected refractive error is the leading cause of visual impairment and blindness worldwide and the leading cause of visual impairment in the United States, where approximately 5.5% of adults over age 40 have vision impairment from uncorrected refractive error. Correcting refractive errors is one of the simplest and highest-impact interventions in all of medicine.

Each type of refractive error results from a different structural feature of the eye and presents with a characteristic pattern of blurred vision. Severity is measured in diopters (D)—a unit of optical power that describes how strong a correcting lens needs to be. Minus numbers (negative diopters) indicate myopia; plus numbers (positive diopters) indicate hyperopia.

Myopia is the most common refractive error worldwide. In a myopic eye, the eyeball is longer than normal from front to back, or the cornea is more curved than normal. As a result, light from a distant object focuses in front of the retina rather than on it, making distant objects blurry while close objects remain clear. Myopia is classified by severity in diopters of correction needed:

• Low myopia (-0.50 D–-3.00 D): Distant vision is mildly blurred. Glasses or contact lenses provide full correction. The risk of complications is low.
• Moderate myopia (-3.00 D–-6.00 D): Distance vision is significantly impaired without correction. The risk of associated eye complications begins to rise.
• High myopia (-6.00 D or stronger): associated with serious complications, including retinal detachment, glaucoma, cataract, and myopic macular degeneration—a form of central vision loss from stretching of the retina. Approximately 10% of the global population is expected to have high myopia by 2050.
• Pathological or degenerative myopia (-8.00 D–-10.00 D or stronger): Structural changes develop in the retina and choroid (the vascular layer beneath the retina), increasing the risk of choroidal neovascularization (abnormal blood vessel growth) and permanent vision loss even with optimal correction.

Hyperopia occurs when the eyeball is shorter than normal, or the cornea is too flat, causing light to focus behind the retina rather than on it. In mild hyperopia, the eye’s natural focusing muscle (the ciliary muscle) can compensate by increasing its contraction—allowing relatively clear near and distance vision at the cost of eye strain and fatigue. In higher degrees of hyperopia, this compensation is insufficient, and both near and distant objects appear blurry. Young children with significant undetected hyperopia may develop esotropia (crossed eyes) because the extra focusing effort triggers excessive inward eye convergence. Hyperopia affects up to 20% of children under age 6.

Astigmatism occurs when the cornea or lens is not perfectly round but instead is shaped more like a football than a basketball—curved more steeply in one direction than another. This causes light to focus at multiple points rather than one, producing blurred or distorted vision at all distances. Astigmatism accounts for 13–40% of all refractive errors and affects approximately 5–10% of preschool-aged children. It most commonly occurs alongside myopia or hyperopia. The axis and degree of the astigmatism are both measured and corrected in the spectacle or contact lens prescription.

Presbyopia is an age-related loss of the eye’s ability to focus on near objects. The crystalline lens inside the eye is normally flexible and changes shape to focus at different distances (a process called accommodation). With age, the lens gradually hardens and loses this flexibility, making it increasingly difficult to focus on close objects such as text or a phone screen. Presbyopia is universal—it develops in virtually all adults between ages 45 and 55, regardless of prior refractive status. People who were previously nearsighted may notice that their uncorrected near vision actually improves temporarily as presbyopia develops (since their myopia partially compensates), but eventually they require near-vision correction just as much as everyone else. Presbyopia is the leading cause of near-vision impairment in the world, affecting approximately 826 million people globally who lack access to adequate near-vision correction.

Anisometropia means having significantly different refractive errors in the two eyes. When one eye needs a much stronger prescription than the other, the brain has difficulty fusing the two differently sized images it receives, causing visual discomfort, eyestrain, and headaches. Anisometropia is clinically important in children because it is a major cause of amblyopia (lazy eye)—the developing brain tends to suppress the image from the more blurred eye, allowing that eye’s visual pathways to remain underdeveloped. Spherical anisometropia of one diopter or more significantly increases the risk of esotropia; cylindrical anisometropia of one diopter or more increases the risk of exotropia.

Keratoconus is a progressive condition in which the cornea gradually thins and bulges outward into a cone-like shape, producing a complex, irregular astigmatism that cannot be fully corrected with standard spectacle lenses. Because of its progressive nature and the need for specialized management, keratoconus is covered in full detail in the Keratoconus conditions page.

Refractive errors arise from a mismatch between the optical power of the eye’s components and the physical length of the eyeball. Understanding the underlying mechanisms helps explain why refractive errors develop, why they are increasing in prevalence, and why some forms respond to preventative strategies while others do not.

The most important determinant of myopia is axial length—how long the eyeball is from front to back. A normal adult eye is approximately 23 to 25 mm in length. Each additional millimeter of axial length corresponds to approximately three diopters of myopia. In myopia, excessive axial elongation of the eyeball causes the focal point of light to land in front of the retina. Corneal curvature is the second major optical parameter—a steeper (more curved) cornea has greater optical power and contributes to myopia when excessively curved. In hyperopia, the opposite applies: the eye is shorter than normal and the cornea flatter than normal, shifting the focal point behind the retina.

Genetics plays a powerful role in refractive error development. Having one myopic parent roughly doubles the risk of developing myopia; having two myopic parents increases it approximately six-fold. More than 200 genetic loci have been associated with myopia in genome-wide association studies. For hyperopia and astigmatism, similarly strong genetic contributions have been identified. However, the dramatic global increase in myopia prevalence over recent decades—particularly in East Asian populations where rates have reached 80–90% in young adults—cannot be explained by genetics alone and has been driven primarily by environmental changes.

The modern myopia epidemic is driven by specific lifestyle changes associated with urbanization and education. Two environmental factors have the strongest evidence:

• Near work: Sustained near visual activity (reading, screen use, close computer work) is associated with myopia development and progression. The biological mechanism involves the retina responding to the sustained near focal demand by signaling increased axial eye growth. This is consistent with the higher rates of myopia in populations with high educational demands.
• Reduced time outdoors: Time spent outdoors is strongly and independently protective against myopia onset and progression. The protective mechanism is thought to involve bright outdoor light stimulating the release of dopamine in the retina, which inhibits axial elongation. Studies have consistently shown that children who spend more time outdoors develop myopia less often and less severely, regardless of how much near work they do. The light intensity outdoors (10,000 to 100,000 lux) is dramatically higher than in typical indoor environments (300 to 500 lux), and this difference appears critical to the protective effect.

Presbyopia is caused by the gradual hardening of the crystalline lens over a lifetime. The lens is normally elastic, and its shape is actively changed by the ciliary muscle to focus at different distances. As proteins inside the lens cross-link with age, the lens loses its flexibility, and the ciliary muscle loses its ability to change the lens’s shape. By the mid-40s, the amplitude of accommodation—the range over which the eye can adjust focus—decreases enough to make near vision difficult without correction. This process is irreversible and universal; it affects everyone regardless of their baseline refractive status.

Astigmatism arises when the cornea or lens develops an uneven curvature—more steeply curved in one meridian than the perpendicular one, like the side of a ball versus the end of a ball. Corneal astigmatism is largely determined by genetics. Irregular astigmatism—astigmatism that cannot be corrected with standard cylindrical lenses—can be caused by corneal surface disease, keratoconus, prior corneal surgery, or trauma.

• Family history of myopia: Having one myopic parent approximately doubles risk; having two myopic parents increases risk approximately six-fold.
• Time spent indoors: Children who spend limited time outdoors have significantly higher rates of myopia onset and faster progression. Each additional hour per day outdoors reduces risk meaningfully.
• High near-work demands: Sustained reading and screen time, particularly at close distances without breaks, are associated with myopia development.
• Urban environment: Myopia is substantially more prevalent in urban than rural populations globally, likely reflecting differences in outdoor time, indoor lighting, and near-work demands.
• East Asian ethnicity: Populations of Chinese, Japanese, Korean, and Southeast Asian descent have dramatically higher myopia prevalence than European-ancestry populations—in part reflecting genetic susceptibility and in part the extreme educational pressures in these regions.
• Younger age of onset: Children who develop myopia before age 10 tend to progress more rapidly and reach higher final prescriptions than those with later onset.

• Family history: Both hyperopia and astigmatism have strong hereditary components.
• Prematurity: Premature infants are more likely to have significant hyperopia and astigmatism.
• Down syndrome: This is associated with higher rates of both hyperopia and astigmatism.
• Ethnicity: Astigmatism prevalence varies by population; certain forms of astigmatism (against-the-rule astigmatism) are more common in older adults and in some ethnic groups.

• Age: Presbyopia affects virtually all adults between ages 45 and 55. No lifestyle factors prevent it.
• Prior hyperopia: Hyperopic individuals tend to notice presbyopia symptoms earlier because they already use more accommodative effort for near vision.
• Systemic diseases: Certain systemic conditions, including uncontrolled diabetes and multiple sclerosis, can accelerate presbyopia-like symptoms by affecting lens metabolism or ciliary muscle function.
• Medications: Some medications, particularly anticholinergics and antihistamines, reduce accommodation by their systemic effects on ciliary muscle function.

Refractive error screening begins in infancy and continues throughout life. Early detection is especially important in children because uncorrected refractive error during visual development leads to amblyopia and—for uncorrected hyperopia—esotropia. The American Academy of Pediatrics (AAP) recommends vision screening at every well-child visit from birth through school age, escalating from basic red reflex testing in infants to instrument-based photoscreening and visual acuity testing in preschoolers and schoolchildren.

The red reflex test screens newborns and infants for significant optical media problems. Instrument-based photoscreening devices (such as the Welch Allyn SPOT Vision Screener and PlusoptiX) detect refractive errors, anisometropia, and other risk factors for amblyopia in children too young to cooperate with standard eye chart testing. Formal visual acuity testing with age-appropriate charts (Lea symbols®, HOTV letters, Snellen chart) is standard from age 3 to 4 onward. A comprehensive dilated eye examination by an ophthalmologist or optometrist—including cycloplegic refraction with drops that relax the focusing muscle—is the most accurate way to measure the full refractive error, particularly in children who compensate with active accommodation and appear to have normal vision on non-cycloplegic testing.

Adults should have comprehensive eye examinations every one to two years, and annually after age 60 or if they have diabetes, a family history of glaucoma, or other ocular risk factors. Many adults in the United States live with correctable refractive error that has never been formally measured or treated.

Myopia caused by genetic susceptibility cannot be prevented. However, the dramatic rise in myopia rates worldwide is largely driven by environmental changes, and several evidence-based preventative strategies have been validated:

• Spend more time outdoors: the most well-supported preventative intervention. Studies and meta-analyses consistently show that one to two additional hours of outdoor time per day significantly reduces myopia onset in children. Schools in Taiwan and China that introduced mandatory outdoor recess time reduced myopia incidence in participating children. Outdoor light intensity—not physical activity per se—appears to be the active mechanism.
• Follow the 20-20-20 rule during near work: every 20 minutes of near-distance work, look at something at least 20 feet away for 20 seconds. This reduces sustained accommodative demand and gives the visual system a brief rest.
• Maintain adequate working distance: Reading or screen use at distances less than 20 to 30 cm (about 8 to 12 inches) is associated with faster myopia progression. Keeping reading material and screens at a comfortable arm’s length reduces the convergence and accommodative demand.
• Avoid prolonged screen use in young children: The AAP recommends limiting screen time for young children not only for developmental reasons but because of the potential myopia-inducing effect of sustained near visual activity.

For children who already have myopia, several treatments have been shown to slow the rate of progression (see Treatment section). There is currently no intervention that prevents presbyopia or age-related lens changes.

The hallmark symptom of all refractive errors is blurred vision—but the pattern of blurring, when it occurs, and what tasks are affected differ significantly by the type of error. Many people adapt to gradual vision changes without recognizing them, making routine eye examinations important for detecting refractive error even when no symptoms are consciously noticed.

• Blurred distance vision: difficulty seeing distant objects such as road signs, whiteboards, television screens, and the faces of people across a room. Close-up vision (reading, phone screens) remains clear.
• Squinting to see at a distance: Partially closing the eyelids reduces the aperture of the eye, slightly sharpening distance vision temporarily.
• Headaches: These can occur from the visual strain of trying to see clearly at a distance, or from prolonged squinting.
• Eye fatigue and difficulty driving, especially at night: Night myopia is a recognized phenomenon in which the pupil dilates in low light, increasing the effect of the optical error and worsening distance blur.
• Holding objects close: Young children who are significantly myopic tend to hold books, devices, and toys very close to their faces.

• Blurred near vision: Nearby objects appear blurry or require effortful concentration to bring into focus. In mild hyperopia, the eye compensates automatically and the person may be unaware of any problem.
• Eye strain, headaches, and eye fatigue: These can happen particularly after sustained reading, screen use, or close work, from the constant effort of maintaining focus through active accommodation.
• Difficulty concentrating on close tasks: Children with undetected hyperopia frequently struggle with reading and classwork, mistakenly appearing inattentive or having a learning difficulty.
• Crossed eyes in children (esotropia): Significant undetected hyperopia in young children can cause an inward eye turn from the excessive convergence that accompanies the extra focusing effort.

• Blurred or distorted vision at all distances: Straight lines may appear tilted or wavy; letters may appear smeared or shadowed.
• Eyestrain and headaches: These can happen particularly with reading or computer use.
• Difficulty seeing fine detail: Detail-oriented work such as reading small print or intricate tasks becomes tiring and imprecise.
• Tilting the head to see more clearly: Some people unconsciously tilt their head to use the better-focused meridian of their astigmatism.

• Difficulty reading small print at normal arm’s length: the classic presenting symptom. Text that was previously easy to read without glasses requires holding the reading material further away.
• Needing brighter light to read: The accommodating eye needs more contrast to compensate for reduced depth of focus.
• Eyestrain and headaches after reading or close work: Even with the reading material held far away, the eyes tire quickly.
• Temporarily blurred distance vision after reading: The ciliary muscle becomes fatigued from the sustained effort of near focus, and distance vision may be transiently blurry when looking up from near work.

• In infants and preschool children (birth to age 5): Refractive errors are usually not described by the child. Signs include holding objects very close, sitting close to the television, squinting, frequent eye rubbing, avoiding near activities (in hyperopia), or an inward-turning eye. Routine screening at well-child visits is the primary detection tool.
• In school-age children (ages 6 to 12): Myopia commonly begins to develop and progress in this age range. Children may have difficulty reading the classroom board, show declining school performance, or squint at screens and books. Annual vision screening and comprehensive eye exams are important at this stage.
• In adolescents and young adults (teens to mid-30s): Myopia often continues to progress, particularly if the person spends many hours studying or on screens. New contact lens and eyeglass prescriptions may be needed frequently. Laser-assisted in situ keratomileusis (LASIK) eligibility typically begins when the prescription has been stable for one to two years.
• In adults 40 to 55: Presbyopia onset is the defining visual change in this age range. People who previously needed no glasses for near vision suddenly find reading glasses necessary. People who wore glasses or contacts for distance vision may find they need bifocals or separate near-vision glasses.
• In adults 55 and older: Both presbyopia and the risk of additional age-related eye conditions (cataract, glaucoma, macular degeneration) increase. Progressive-lens glasses or multifocal contact lenses are commonly used. Cataract surgery, when needed, often provides an opportunity to simultaneously correct refractive error through the choice of intraocular lens implant.

A refractive error is measured by an optometrist or ophthalmologist. Diagnosis is straightforward, safe, and noninvasive. The full evaluation typically takes 30 to 60 minutes and includes measurement of visual acuity, objective assessment of the refractive error, and a refraction—a process of systematically testing different lens combinations to find the correction that produces the sharpest vision.

The standard Snellen eye chart—the familiar letter chart read from 20 feet—measures the sharpness of central vision and establishes a baseline. Visual acuity is recorded as a fraction: 20/20 means a person sees at 20 feet what a normally-sighted person sees at 20 feet; 20/200 means a person needs to be 20 feet away to see what a normally-sighted person can see at 200 feet. Near visual acuity is measured with a reading card at standard near working distance (approximately 14 inches). Visual acuity in each eye is tested separately to identify anisometropia and amblyopia.

Refraction is the central measurement in refractive error diagnosis. Two types are performed.

• Objective refraction: A device called an autorefractor or a retinoscope measures the refractive state of the eye without requiring responses from the patient. The autorefractor projects a pattern onto the retina and measures how light reflects back, computing the approximate prescription automatically. Retinoscopy—performed with a handheld light and lens set—is the traditional method and is particularly useful in young children, cognitively impaired patients, and those who cannot cooperate with automated testing. These tests give the clinician a starting point for the subsequent subjective refraction.
• Subjective refraction: The clinician presents different lens combinations using a phoropter (the large instrument with many lenses that patients look through during an eye exam) while the patient reads the eye chart and reports which is clearer. The final prescription chosen is the minimum correction that produces the best-corrected visual acuity. This process determines the sphere (overall power), cylinder (astigmatism correction), and axis (the orientation of the astigmatism correction) for each eye.

In children and young adults, the eye’s ciliary muscle can actively compensate for hyperopia by contracting, masking the true refractive error on a standard refraction. Cycloplegic refraction uses eye drops (typically cyclopentolate 1% or atropine 1%) that temporarily paralyze the ciliary muscle and dilate the pupil. This reveals the full, uncompensated refractive error—including hidden hyperopia—and is the standard of care for any child undergoing a comprehensive eye examination. Without cycloplegia, significant hyperopia can be completely missed. The drops take 30 to 45 minutes to work fully and wear off over several hours (atropine may take one to two weeks).

When irregular astigmatism, keratoconus, or refractive surgery candidacy is being evaluated, corneal topography or tomography maps the curvature of the entire corneal surface with high precision. Standard topography uses reflected light patterns to map the anterior surface; Scheimpflug tomography (Pentacam®) maps both the anterior and posterior surfaces and measures corneal thickness throughout, revealing early keratoconus and other corneal irregularities that would otherwise be missed.

A comprehensive eye examination also includes slit-lamp evaluation of the anterior eye structures, dilated fundus examination of the optic nerve and retina, and measurement of intraocular pressure—to detect cataract, retinal changes, and glaucoma that are associated with high myopia, and to screen for glaucoma and macular disease in all adult patients.

Refractive errors are among the most treatable conditions in medicine. Options range from spectacle lenses and contact lenses—which provide full, safe correction for all ages—to laser surgery and lens implants that provide permanent correction without the ongoing need for glasses. For children who have myopia, specific treatments can slow the rate of progression and reduce the likelihood of developing high myopia with its associated risks. Your optometrist or ophthalmologist will help you choose the best approach based on your prescription, age, lifestyle, and personal preferences.

Eyeglasses are the safest, most universally accessible, and most commonly used method of correcting all types of refractive error. A lens placed in front of the eye adds or subtracts optical power, bending light so that it focuses correctly on the retina. Minus-power (concave) lenses correct myopia; plus-power (convex) lenses correct hyperopia; cylindrical lenses correct astigmatism; bifocal or progressive lenses correct presbyopia while maintaining distance vision. Modern lens materials—including high-index plastics, polycarbonate, and Trivex®—are significantly thinner, lighter, and more impact-resistant than glass and older plastic lenses. Antireflective coatings reduce glare and improve clarity. Photochromic (Transitions®) lenses darken in ultraviolet (UV) light. Spectacle lenses are suitable for any prescription, any age, and any medical situation. They carry no risk of infection, corneal damage, or surgical complications.

Contact lenses sit directly on the tear film of the cornea and correct refractive error by adding optical power directly at the eye’s surface. Soft contact lenses—made from hydrogel or silicone hydrogel materials—are the most commonly used type and are available as single-use daily disposables, two-weekly replacement, or monthly replacement lenses. Daily disposables are the healthiest option for most people, as a fresh sterile lens is worn each day. Silicone hydrogel lenses transmit significantly more oxygen to the cornea than older hydrogel materials. Toric contact lenses correct astigmatism; multifocal contact lenses address presbyopia by incorporating near and distance zones into a single lens. Rigid gas-permeable (RGP) lenses are made from a firm oxygen-permeable material; they provide sharper optics than soft lenses in many eyes and are the preferred contact lens for irregular corneas (keratoconus, post-surgical astigmatism). Orthokeratology (Ortho-K) lenses are specially designed rigid lenses worn overnight that temporarily reshape the cornea during sleep, allowing clear vision without any correction during waking hours. Scleral contact lenses are large-diameter rigid lenses that vault completely over the cornea and rest on the sclera; they are particularly effective for highly irregular corneas and severe dry eye. Contact lenses require strict hygiene—sleeping in lenses (other than approved extended-wear types), using tap water, and swimming while wearing lenses all dramatically increase the risk of microbial keratitis (corneal infection). Contact lens-related corneal infection, while uncommon, is a serious complication that can cause permanent vision loss.

For children with myopia, certain treatments have been shown to slow the rate of axial elongation and prescription progression, reducing the likelihood of reaching high myopia with its associated risks. These are distinct from correction—they treat the underlying progression rather than simply compensating for it.

• Atropine eye drops (low-dose, 0.01–0.05% concentration): the most extensively studied pharmacological myopia control treatment. Nightly application of very low-dose atropine drops has been shown in randomized trials to slow myopia progression by approximately 50–77% compared to placebo, with minimal side effects at low doses (slight pupil dilation, minimal near-vision blurring). Mechanism: reduces retinal signaling that drives axial elongation, possibly through dopamine pathways. Widely used in Asia; increasingly adopted in the United States.
• Orthokeratology (Ortho-K): overnight rigid contact lenses that reshape the corneal surface, providing clear daytime vision without lenses while also slowing axial elongation. Multiple trials demonstrate a 40–55% reduction in myopia progression compared to standard glasses. Particularly popular in Asia. Requires good compliance with lens care to avoid infection risk.
• MiSight® 1 day contact lenses: U.S. Food and Drug Administration (FDA)-cleared daily disposable soft contact lenses specifically designed for myopia control. They use concentric rings that defocus the peripheral retina (a mechanism thought to reduce the retinal signal driving axial growth). Clinical trials showed approximately 59% reduction in myopia progression compared to standard single-vision contact lenses.
• Peripheral defocus spectacle lenses: specialized glasses with a center zone for distance correction and a peripheral zone that creates myopic defocus on the peripheral retina. Multiple designs have shown a 30–50% reduction in progression in clinical trials.
• Increased outdoor time: As discussed in the Prevention section, consistent evidence supports outdoor time as a myopia control measure. Children who are already myopic and increase outdoor time to one to two hours per day show meaningfully slower progression.

Refractive surgery uses laser technology or implanted lenses to permanently alter the eye’s optical power, reducing or eliminating the need for glasses or contact lenses. Most surgical options are available to adults whose prescription has been stable for at least one to two years and who meet other criteria for candidacy (adequate corneal thickness, healthy ocular surface, no keratoconus or corneal disease). All refractive surgery carries small but real risks that must be weighed against the benefit of spectacle and contact lens independence.

• Laser in situ keratomileusis (LASIK): the most commonly performed laser eye surgery worldwide. A thin flap is created in the corneal surface using a laser (femtosecond laser) or blade; the underlying stroma is then reshaped by an excimer laser to correct the refractive error; the flap is replaced. Recovery is rapid—most patients see clearly within 24 hours. FDA-approved for myopia, hyperopia, and astigmatism. Side effects include temporary dry eye (very common, typically resolving within months), halos and glare around lights at night, and very rarely (approximately 0.1%) flap complications. Contraindicated in keratoconus.
• Photorefractive keratectomy (PRK): An excimer laser reshapes the corneal surface directly, without creating a flap. The surface cells (epithelium) are removed first and regenerate naturally over three to five days post-procedure. Visual recovery takes longer than LASIK (days to weeks rather than hours), and there is more short-term discomfort. However, PRK does not create a flap and is preferred for patients with thin corneas, physically demanding occupations, or contact sports where a flap could be disturbed.
• Small incision lenticule extraction (SMILE): a newer procedure in which a femtosecond laser creates a lens-shaped disc of corneal tissue (a lenticule) that is extracted through a small incision without creating a flap. Recovery is somewhat slower than LASIK for very sharp vision, but faster than PRK. It avoids flap-related risks and may cause less dry eye than LASIK. FDA-approved for myopia and astigmatism.
• Phakic intraocular lens (implantable collamer lens—ICL): For patients with prescriptions too strong for laser surgery or corneas too thin, a small artificial lens is surgically implanted in front of the natural lens without removing it. The Visian® ICL™ (EVO ICL) is the most widely used phakic intraocular lens (IOL), FDA-approved for correction of high myopia (-3.00 to -20.00 D). It provides excellent optical quality and is reversible—the lens can be removed if needed.
• Refractive lens exchange (RLE): The natural crystalline lens is removed (the same operation as cataract surgery) and replaced with an artificial intraocular lens (IOL) of the desired power. RLE eliminates the need for glasses for distance vision and, with premium multifocal or extended-depth-of-focus IOLs, can also address presbyopia. It is particularly appropriate for patients over age 45 who are beginning to develop presbyopia or who have high prescriptions not suitable for laser surgery. The trade-off is the permanent loss of natural accommodation and the small surgical risks of intraocular surgery.
• Conductive keratoplasty (CK): uses radiofrequency energy applied to spots on the peripheral cornea to steepen it, temporarily correcting hyperopia and presbyopia. Less commonly used today due to regression of effect over time.

Presbyopia cannot be reversed by any currently available treatment, but it can be corrected through several approaches tailored to the individual’s lifestyle and preferences:

• Reading glasses: simple over-the-counter or prescription plus-power glasses used only for near tasks. The simplest, lowest-cost solution.
• Bifocal glasses: These are lenses with a distance correction in the upper portion and a near correction in the lower portion, separated by a visible line.
• Progressive lenses: lenses with a gradual transition from distance correction at the top to near correction at the bottom, with no visible dividing line. The most widely used presbyopia correction in adults who also need distance glasses.
• Multifocal or monovision contact lenses: Multifocal contacts incorporate near and distance zones; monovision corrects one eye for distance and the other for near, allowing the brain to blend the two images. Both approaches involve some compromise in optical quality compared to single-vision correction.
• Vuity™ (pilocarpine 1.25% ophthalmic solution): FDA-approved in October 2021 as the first prescription eye drop specifically for presbyopia. Pilocarpine constricts the pupil, increasing depth of focus and improving near vision for up to six hours. Used once daily in each eye. Side effects include headache, brow ache, and reduced night vision from the smaller pupil. Most effective for mild to moderate presbyopia in patients aged 40 to 55.
• Refractive lens exchange with multifocal or extended depth-of-focus (EDOF) IOL: As described above, replacing the natural lens with a premium artificial lens can address both presbyopia and other refractive errors simultaneously, providing a permanent solution.

Refractive errors are among the most manageable health conditions a person can have. With the right correction—whether spectacles, contact lenses, or surgery—the vast majority of people with refractive errors can achieve excellent vision and live completely normal, unrestricted lives. Glasses and contact lenses are safe, reliable, and continuously improving in optical quality, comfort, and aesthetics. Laser surgery offers millions of people the freedom to see without any correction, and the range of surgical and pharmacological options for presbyopia continues to expand.

For parents, the most important message is that children’s eyes should be examined early and regularly, and that any refractive error found should be fully corrected with glasses—even if the child does not complain. The consequences of uncorrected refractive error in early childhood—amblyopia, strabismus, and permanently limited visual development—are entirely preventable with timely treatment. For parents concerned about myopia progression in their children, several evidence-based slowing strategies are available and worth discussing with a pediatric ophthalmologist or myopia-specialist optometrist. Spending more time outdoors is the simplest, safest, and most universally recommended step.

To further your understanding of your diagnosis and to contribute to cutting-edge research, consider participating in a clinical trial so clinicians and scientists can learn more about causes, symptoms, treatment, and prevention of refractive error and related disorders. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.