Refractive Error

Refractive error is the failure of the eye to focus parallel light rays precisely on the retina, causing blurred vision. It includes myopia (short sightedness), hyperopia (long sightedness), astigmatism and presbyopia. It is the commonest cause of visual impairment worldwide and the leading cause of correctable vision loss, affecting more than 2 billion people. Spectacles, contact lenses or surgery correct it, and uncorrected error in children can cause amblyopia and affect learning.

• Types: spherical errors (myopia: eye too long or optical power too strong; hyperopia: eye too short or optical power too weak), astigmatism (unequal curvature of the cornea or lens), presbyopia (age related loss of accommodation), anisometropia (different refractive error in the two eyes).
• Causes and risk factors: genetics, axial length growth, prematurity, family history, near work and low outdoor exposure, age, diabetes (fluctuating), cataract, keratoconus, medications, pregnancy.
• Complications of uncorrected error: reduced school performance, amblyopia, strabismus, eye strain, headaches, falls and driving risk in adults, reduced quality of life.

• Blurred distance vision (myopia), blurred near vision or eye strain (hyperopia and presbyopia), distorted or ghosted vision (astigmatism), squinting, headaches, eye rubbing, sitting close to the television, holding books close or far, closing one eye, difficulty seeing the board, poor night vision.
• Children are often asymptomatic; head tilt, squint, poor reading and clumsiness may be clues.
• Examination: distance and near visual acuity with and without pinhole (improves in refractive error), cover test, red reflex, corneal reflex, ocular health.
• Red flags: sudden change in vision, visual acuity not improving with pinhole, monocular double vision, flashes and floaters, field loss, pain, redness, leukocoria, white pupil on a photograph, squint, nystagmus, a rapid myopic shift (diabetes, cataract, keratoconus, medications), anisometropia in a child, headache with vomiting.

• Visual acuity with a logMAR or Snellen chart (children: age appropriate charts), pinhole test, autorefraction, retinoscopy, subjective refraction.
• Cycloplegic refraction in children, in suspected hyperopia or accommodative esotropia: cyclopentolate 1 percent, 1 drop in each eye, repeat after 5 minutes, measure after 30 to 40 minutes (cyclopentolate 0.5 percent in infants under 12 months; atropine 1 percent in selected young children with esotropia, twice daily for 3 days).
• Keratometry and corneal topography when astigmatism is irregular or keratoconus is suspected.
• Slit lamp and fundus examination; axial length measurement (myopia control).
• Screening: school and pre-school vision screening, red reflex test at birth and 6 to 8 weeks.
• Differentials for reduced vision: cataract, amblyopia, macular disease, optic neuropathy, glaucoma, corneal disease, retinal detachment, diabetic eye disease.

• Spectacles (first line): single vision, bifocal or progressive lenses, with anti-reflective coating and UV protection; polycarbonate lenses for children and sports.
• Contact lenses: soft daily disposable lenses (preferred), toric for astigmatism, multifocal for presbyopia, rigid gas permeable for irregular astigmatism; teach hygiene and safe wear.
• Refractive surgery (stable prescription for at least 1 to 2 years, age 18 or over): laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), small incision lenticule extraction (SMILE); phakic intraocular lens (implantable collamer lens) for high myopia; refractive lens exchange for hyperopia and presbyopia.
• Children: prescribe correction for amblyopia risk or symptoms; spectacles must be worn full time; treat amblyopia by occlusion or atropine penalisation; review every 6 to 12 months.
• Myopia progression control in children: low dose atropine 0.01 to 0.05 percent eye drops at night, orthokeratology, dual focus contact lenses or defocus spectacle lenses, plus at least 2 hours of outdoor time daily.
• Adults: eye examination every 2 years (annually after 60 years and in diabetes or family history of glaucoma).
• Education on glare, night driving, and the legal visual requirements for driving.
• Refer to ophthalmology for red flags, amblyopia, squint, high refractive error, rapid change, suspected keratoconus or surgical interest.