- HYPERMETROPIA
- Hypermetropia (hyperopia) or long-sightedness is the refractive state of the eye wherein parallel rays of light coming from infinity are focused behind the retina with accommodation being at rest
- Thus, the posterior focal point is behind the retina, which therefore receives a blurred image.
- Etiology
- Axial hypermetropia
- Commonest form.
- In this condition the total refractive power of eye is normal but there is an axial shortening of eyeball.
- About 1–mm shortening of the antero- posterior diameter of the eye results in 3 dioptres of hypermetropia.
- Curvatural hypermetropia
- condition in which the curvature of cornea, lens or both is flatter than the normal results in a decrease in the refractive power of eye.
- About 1 mm increase in radius of curvature results in 6 dioptres of hypermetropia.
- Index hypermetropia
- occurs due to decrease in refractive index of the lens in old age.
- It may also occur in diabetics under treatment.
- Positional hypermetropia results from posteriorly placed crystalline lens.
- Absence of crystalline lens
- either congenitally or acquired (following surgical removal or posterior dislocation) leads to aphakia — a condition of high hypermetropia.
- Clinical types
- Simple or developmental hypermetropia
- commonest form
- results from normal biological variations in the development of eyeball.
- It includes axial and curvatural hypermetropia.
- Pathological hypermetropia
- results due to either congenital or acquired conditions of the eyeball which are outside the normal biological variations of the development.
- Index hypermetropia (due to acquired cortical sclerosis),
- Positional hypermetropia (due to posterior subluxation of lens),
- phakia (congenital or acquired absence of lens)
- Consecutive hypermetropia (due to surgically over-corrected myopia).
- results due to either congenital or acquired conditions of the eyeball which are outside the normal biological variations of the development.
- Functional hypermetropia
- results from paralysis of accommodation
- seen in patients with third nerve paralysis and internal ophthalmoplegia.
- Total hypermetropia = latent + manifest (facultative + absolute).
- Total hypermetropia
- total amount of refractive error, which is estimated after complete cycloplegia with atropine
- It consists of latent and manifest hypermetropia.
- Latent hypermetropia
- amount of hypermetropia (about 1D) which is normally corrected by the inherent tone of ciliary muscle.
- The degree of latent hypermetropia is high in children and gradually decreases with age.
- The latent hypermetropia is disclosed when refraction is carried after abolishing the tone with atropine.
- Manifest hypermetropia i
- remaining portion of total hypermetropia, which is not corrected by the ciliary tone.
- It consists of two components, the facultative and the absolute hypermetropia.
- Facultative hypermetropia constitutes that part which can be corrected by the patient’s accommodative effort.
- Absolute hypermetropia is the residual part of manifest hypermetropia which cannot be corrected by the patient’s accommodative efforts.
- Total hypermetropia
- Simple or developmental hypermetropia
- Clinical picture
- Symptoms
- Asymptomatic.
- A small amount of refractive error in young patients can be asymptomatic
- Asthenopic symptoms.
- Occur even when the amount of hypermetropia is fully corrected
- Occur due to sustained accommodative efforts patient develops asthenopic symptoms.
- These include
- tiredness of eyes
- frontal or fronto-temporal headache
- watering
- mild photophobia.
- associated with near work
- increase towards evening.
- Defective vision with asthenopic symptoms.
- Occur when the amount of hypermetropia is such that it is not fully corrected by the voluntary accommodative efforts
- Defective vision only.
- When the amount of hypermetropia is very high, the patients usually do not accommodate (especially adults) and there occurs marked defective vision for near and distance.
- Asymptomatic.
- Signs
- Size of eyeball may appear small as a whole.
- Cornea may be slightly smaller than the normal.
- Anterior chamber is comparatively shallow.
- Fundus examination reveals
- a small optic disc
- which may look more vascular with ill-defined margins
- simulate papillitis (though there is no swelling of the disc, and so it is called pseudopapillitis).
- The retina as a whole may shine due to greater brilliance of light reflections (shot silk appearance).
- a small optic disc
- A-scan ultrasonography (biometry) may reveal a short antero-posterior length of the eyeball.
- Symptoms
- Complications
- Recurrent styes, blepharitis or chalazia
- occur due to infection introduced by repeated rubbing of the eyes, which is often done to get relief from fatigue and tiredness.
- Accommodative convergent squint may develop in children (usually by the age of 2-3 years) due to excessive use of accommodation.
- Amblyopia may develop in some cases.
- anisometropic (in unilateral hypermetropia)
- strabismic (in children developing accommodative squint)
- ametropic (seen in children with uncorrected bilateral high hypermetropia).
- Predisposition to develop primary narrow angle glaucoma.
- The eye in hypermetropes is small with a comparatively shallow anterior chamber. Due to regular increase in the size of the lens with increasing age, these eyes become prone to an attack of narrow angle glaucoma.
- This point should be kept in mind while instilling mydriatics in elderly hypermetropes.
- Recurrent styes, blepharitis or chalazia
- Treatment
- Optical treatment
- prescribe convex (plus) lenses, so that the light rays are brought to focus on the retina
- Fundamental rules for prescribing glasses in hypermetropia include:
- Total amount of hypermetropia should always be discovered by performing refraction under complete cycloplegia.
- The spherical correction given should be comfortably acceptable to the patient. However, the astigmatism should be fully corrected.
- Gradually increase the spherical correction at 6 months interval till the patient accepts manifest hypermetropia.
- In the presence of accommodative convergent squint, full correction should be given at the first sitting.
- If there is associated amblyopia, full correction with occlusion therapy should be started.
- Modes of prescription of convex lenses
- Spectacles are most comfortable, safe and easy method of correcting hypermetropia.
- Contact lenses are indicated in unilateral hypermetropia (anisometropia).
- Refractive surgery for hyperopia
- It should be performed after 20 years of age.
- In general, refractive surgery for hyperopia is not as effective or reliable as for myopia.
- Holmium laser thermoplasty
- used for low degree of hyperopia.
- laser spots are applied in a ring at the periphery to produce central steepening
- Regression effect and induced astigmatism are the main problems.
- Hyperopic PRK
- Done using excimer laser
- Regression effect and prolonged epithelial healing are the main problems encountered.
- Hyperopic LASIK
- effective in correcting hypermetropia upto +4D.
- Conductive keratoplasty (CK)
- nonablative and nonincisional procedure
- cornea is steepened by collagen shrinkage through the radiofrequency energy
- This technique is effective for correcting hyperopia of upto 3D.
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