# Refractive Errors > Refractive errors for FMGE Ophthalmology: myopia, hypermetropia, astigmatism, presbyopia with lens correction, presbyopic additions and degenerative myopia. - Canonical URL: https://prepelephant.com/topics/fmge/ophthalmology/refractive-errors-fmge - Exam / course: FMGE · Subject: Ophthalmology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Refractive Errors", PrepElephant, https://prepelephant.com/topics/fmge/ophthalmology/refractive-errors-fmge ## Direct answer Blurred vision that clears through a pinhole is refractive in origin: light rays fail to focus on the retina in an otherwise healthy eye. In myopia the eye is too long or the cornea too steep, images form in front of the retina, and a minus (concave) lens corrects it; in hypermetropia the eye is too short, and a plus (convex) lens is needed; astigmatism, usually from an unequal corneal curvature, requires a cylindrical lens; and presbyopia is the physiological failure of accommodation after the age of about 40, corrected with near addition. Retinoscopy provides the objective number, subjective refinement provides the prescription. ## What you must remember - Myopia is most often axial (axial length above 24 mm); degenerative myopia beyond 6 D carries risks of lattice degeneration, retinal tears, myopic macular degeneration and retinal detachment. - Hypermetropia is divided into total, latent (masked by accommodation) and manifest components; young children tolerate moderate hypermetropia until ciliary tone fails. - Uncorrected hypermetropia in a child is the classic cause of accommodative esotropia — full cycloplegic correction first, surgery only for the residual deviation. - Regular astigmatism is corrected with a cylinder placed on the corrective axis; irregular astigmatism (corneal scars, keratoconus) responds only to rigid contact lenses — Placido disc and keratometry map the corneal curvature. - Presbyopic additions rise predictably: about +1.0 D at 40 years, +1.5 D at 45, +2.0 D at 50 and +2.5 to +3.0 D by 55 to 60, as the near point recedes. - Anisometropia of roughly 2.5 D or more in childhood invites amblyopia and needs early, full correction of the more ametropic eye. - Definitive options beyond spectacles: contact lenses, excimer laser procedures (PRK on the surface, LASIK under a flap) and, for aphakia, intraocular lens implantation. ## A typical clinic case, worked through A 24-year-old engineering student reports distance blur for a year, worse at the cinema. Unaided vision is 6/60 in each eye; through a pinhole both eyes read 6/9, which already tells you the fundus is probably normal. Cycloplegic retinoscopy with homatropine reveals minus 3.0 D spheres in both eyes with mild astigmatism; subjective refinement gives 6/6. Explain the diagnosis in one line — the eyeball is slightly long — prescribe spectacles, and counsel the two facts that matter: myopia usually stabilises in the mid-twenties, and high myopia justifies periodic dilated fundus examination because of detachment risk. Contrast this with a 45-year-old clerk with 6/6 distance vision who now holds the newspaper at arm's length. His error is presbyopic, not myopic; giving him distance minus lenses would be wrong. He needs a plus addition of about +1.5 D for near work over his distance prescription, reviewed every two to three years as the addition deepens. The pair of cases illustrates the whole topic: same complaint of blur, entirely different optics, and the pinhole plus retinoscopy separate them in minutes. ## How the exam frames it FMGE questions on this topic are almost always one of four types: match the error to its correcting lens; compute or recall the presbyopic addition for an age; identify the complication of degenerative myopia; or decide management of a squinting hypermetropic child. A favourite distractor pairs presbyopia with convex lenses "because the lens becomes too weak" — the lens itself stiffens and the ciliary muscle effect declines; the practical answer, a near addition, is the same. Another classic asks which astigmatism a spectacle cylinder cannot fix; the answer, irregular astigmatism, is a viva staple because it also explains why corneal-scarred patients need rigid lenses rather than thicker glasses. ## Frequently asked questions ### Which lens corrects myopia and why? A concave (minus) diverging lens, because in myopia rays converge in front of the retina and must be diverged to fall on it. ### What causes presbyopia and when does it begin? Age-related loss of lens elasticity and ciliary muscle effectiveness, becoming symptomatic near 40 years when the near point recedes beyond comfortable reading distance. ### How is accommodative esotropia managed? By prescribing the full cycloplegic hypermetropic correction first; the squint shrinks or disappears, and surgery is reserved for any residual deviation. ### Which type of astigmatism is not correctable by spectacles? Irregular astigmatism, from corneal scarring or keratoconus; rigid gas-permeable contact lenses replace the irregular corneal surface. ### What are the dangers of high myopia? Peripheral retinal degeneration and tears, rhegmatogenous retinal detachment, myopic maculopathy and earlier cataract — hence periodic dilated fundus screening.