Refractive Errors — Myopia, Hyperopia, Astigmatism & Presbyopia Guide — Symptoms, Causes & Treatment | MyMedicPlus

Refractive errors are the most common cause of visual impairment worldwide, affecting an estimated 2.7 billion people. They occur when the shape of the eye prevents light from focusing correctly on the retina, resulting in blurred vision. There are four main types: myopia (short-sightedness — difficulty seeing distant objects), hyperopia (long-sightedness — difficulty seeing near objects, though mild hyperopia is often symptom-free in young people), astigmatism (irregular corneal or lens curvature causing blurred or distorted vision at all distances), and presbyopia (age-related loss of near focusing ability affecting virtually everyone over 45 due to lens stiffening). Refractive errors are easily corrected with spectacles, contact lenses, or surgical procedures. Uncorrected refractive errors remain the leading cause of preventable vision impairment globally, particularly in low- and middle-income countries.

Refractive errors result from a mismatch between the optical power of the eye and its axial length, preventing images from focusing sharply on the retina. Myopia: the eye is too long (axial myopia — most common) or the cornea is too curved, causing light to focus in front of the retina. Myopia has increased dramatically in prevalence over recent decades — driven by reduced outdoor time in childhood and increased near work (reading, screen use), likely mediated through reduced retinal dopamine release. High myopia (greater than -6 dioptres) significantly increases the risk of retinal detachment, glaucoma, macular degeneration, and cataract. Hyperopia: the eye is too short or the cornea is too flat, causing light to focus behind the retina. Astigmatism: irregular curvature of the cornea or crystalline lens causing multiple focal points. Presbyopia: progressive stiffening of the crystalline lens reduces accommodative amplitude — begins around age 40-45 and is universal by age 55. Risk factors for myopia progression include Asian ethnicity, parental myopia, limited outdoor time, and high levels of near work.

Myopia: difficulty seeing distant objects clearly (e.g., blackboard, road signs, television) while near vision remains good; squinting to improve focus; eye strain and headaches from sustained distance vision. Hyperopia: difficulty focusing on near objects (children often accommodate adequately and may be asymptomatic); eye strain, headaches, and blurry vision with reading or near tasks; in high hyperopia, even distance vision may be blurred. Astigmatism: blurred or distorted vision at all distances, ghosting or shadowing of images, difficulty with night driving (halos and glare around lights), and eye strain or headaches. Presbyopia: progressive difficulty reading small print at normal arm's length distance — holding reading material further away ('short arm syndrome'), difficulty in dim lighting, eye strain, and headaches after near work. In children: squinting, sitting close to screens, eye rubbing, and poor academic performance may indicate uncorrected refractive error.

Diagnosis of refractive error begins with visual acuity testing using a Snellen chart (or LogMAR chart) — recording distance and near vision in each eye. Refraction (subjective): the optometrist or ophthalmologist identifies the lens power that optimises visual acuity using a phoropter (trial frame with test lenses). Objective refraction: auto-refractometry provides an automated estimate of refractive error. Retinoscopy is used to objectively determine refraction — particularly important in children who cannot reliably respond. In children, cycloplegic refraction (using dilating eye drops such as cyclopentolate to relax accommodation) is essential for accurate measurement, particularly for hyperopia. Corneal topography is used when astigmatism is complex or keratoconus (progressive corneal thinning) is suspected. Axial length biometry (IOLMaster) is used for pre-operative planning in cataract or refractive surgery. Slit-lamp examination and fundus examination should be performed at each optometric or ophthalmologic assessment.

Spectacles: the most common and accessible correction — single vision lenses for myopia, hyperopia, or astigmatism; bifocal or progressive addition lenses for presbyopia. High-index lenses reduce lens thickness for high prescriptions. Contact lenses: soft hydrogel or silicone hydrogel lenses for myopia, hyperopia, and astigmatism; rigid gas-permeable (RGP) lenses for irregular astigmatism (keratoconus). Orthokeratology (Ortho-K): rigid gas-permeable lenses worn overnight temporarily reshape the cornea for daytime clear vision without glasses — also used for myopia control in children. Refractive surgery: LASIK (laser in situ keratomileusis) — flap creation and excimer laser stromal ablation; PRK (photorefractive keratectomy) — surface ablation; SMILE (small incision lenticule extraction) — flapless lenticule removal; implantable collamer lens (ICL) for very high myopia unsuitable for LASIK. Presbyopia correction: reading glasses, multifocal contact lenses, monovision LASIK, or presbyopia-correcting IOL implants at cataract surgery. Myopia control in children: low-concentration atropine eye drops (0.01-0.05%), Ortho-K, multifocal contact lenses, and increased outdoor time (at least 90 minutes/day) reduce myopia progression rates.

Uncorrected high refractive error in children causes amblyopia (lazy eye) — unilateral permanent reduction in visual acuity from inadequate visual stimulation during the critical developmental period (birth to age 7-9 years); amblyopia is irreversible if not treated before age 9 with patching of the better eye and correction of the refractive error. Anisometropia (significantly different prescriptions in each eye) is a particularly potent cause of amblyopia, as the brain suppresses the blurred eye. High myopia (greater than -6 dioptres) carries significantly elevated risks of rhegmatogenous retinal detachment (10 times general population risk, from thinning of peripheral retina), myopic maculopathy (macular degeneration from axial elongation — Forster-Fuchs spot, lacquer cracks), primary open-angle glaucoma (3 times higher risk), and earlier cataract development. Keratoconus — progressive corneal thinning and steepening causing irregular astigmatism — affects approximately 1 in 2,000 people and, untreated, leads to severe progressive visual impairment requiring rigid contact lenses or corneal transplant. Refractive surgery complications include dry eye syndrome, halos, starbursts, and corneal ectasia.

While simple refractive errors cannot be fully prevented, myopia progression in children can be meaningfully slowed. Outdoor time is the most evidence-based preventive measure: at least 90 minutes of outdoor activity per day reduces myopia onset by 50% in children — the mechanism involves retinal dopamine release stimulated by bright outdoor light. Limit prolonged near work; follow the 20-20-20 rule (every 20 minutes of near work, look at something 20 feet away for 20 seconds). Low-dose atropine eye drops (0.01%) slowed myopia progression by 50-60% in the ATOM2 and LAMP studies. Orthokeratology and peripheral defocus soft contact lenses reduce myopia progression by 40-60%. Regular eye examinations from early childhood allow early identification and correction of refractive errors, preventing amblyopia (lazy eye) from uncorrected high refractive errors. All children should have vision screening at school entry.

See an optometrist if you notice blurred vision at any distance, eye strain or headaches with visual tasks, squinting, double vision, or difficulty with night driving. Children should have their vision checked before starting school and whenever there is concern about visual problems, learning difficulties, or unusual behaviour such as sitting very close to screens or squinting. Seek urgent ophthalmology review if you experience sudden vision loss, new floaters, flashing lights, or a curtain across your visual field — these may indicate retinal detachment, particularly in highly myopic patients. People with high myopia (greater than -6 dioptres) should have annual dilated fundus examinations to monitor for myopic maculopathy, retinal holes, and lattice degeneration. Adults over 40 should have regular comprehensive eye exams to detect presbyopia and screen for glaucoma.