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

Hypermetropia may be axial, curvatural, index, positional and due to absence of lens.

1. Axial hypermetropia is by far the 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 anteroposterior diameter of the eye results in 3 dioptres of hypermetropia.

2. Curvatural hypermetropia is the condition in which the curvature of cornea, lens or both is flatter than the normal resulting in a decrease in the refractive power of eye. About 1 mm increase in radius of curvature results in 6 dioptres of hypermetropia.

3. Index hypermetropia occurs due to decrease in refractive index of the lens in old age. It may also occur in diabetics under treatment.

4. Positional hypermetropia results from posteriorly placed crystalline lens.

5. Absence of crystalline lens either congenitally or acquired (following surgical removal or posterior dislocation) leads to aphakia — a condition of high hypermetropia.

Clinical types

There are three clinical types of hypermetropia:

1. Simple or developmental hypermetropia is the commonest form. It results from normal biological variations in the development of eyeball. It includes axial and curvatural hypermetropia.

2. Pathological hypermetropia results due to either congenital or acquired conditions of the eyeball which are outside the normal biological variations of the development.

It includes :

�* Index hypermetropia (due to acquired cortical sclerosis),

�* Positional hypermetropia (due to posterior subluxation of lens),

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* Aphakia (congenital or acquired absence of lens)

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* Consecutive hypermetropia (due to surgically over-corrected myopia).

3. Functional hypermetropia results from paralysis of accommodation as seen in patients with third nerve paralysis and internal ophthalmoplegia. Nomenclature (components of hypermetropia)

Nomenclature for various components of the hypermetropia is as follows:

Total hypermetropia is the total amount of refractive error, which is estimated after complete cycloplegia with atropine. It consists of latent and manifest hypermetropia.

1. Latent hypermetropia implies the 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.

2. Manifest hypermetropia is the remaining portion of total hypermetropia, which is not corrected by the ciliary tone. It consists of two components, the facultative and the absolute hypermetropia.

i. Facultative hypermetropia constitutes that part which can be corrected by the patient's accommodative effort.

ii. Absolute hypermetropia is the residual part of manifest hypermetropia which cannot be corrected by the patient's accommodative efforts.

Thus, briefly:

Total hypermetropia = latent + manifest (facultative + absolute)

Clinical picture

Symptoms

In patients with hypermetropia the symptoms vary depending upon the age of patient and the degree of refractive error.

These can be grouped as under:

1. Asymptomatic.

A small amount of refractive error in young patients is usually corrected by mild accommodative effort without producing any symptom.

2. Asthenopic symptoms.

At times the hypermetropia

is fully corrected (thus vision is normal) but due to sustained accommodative efforts patient develops asthenopic sysmtoms.

These include: tiredness of eyes, frontal or fronto-temporal headache, watering and mild photophobia.

These asthenopic symptoms are especially associated with near work and increase towards evening.

div>3. Defective vision with asthenopic symptoms.

When the amount of hypermetropia is such that it is not fully corrected by the voluntary accommodative efforts, then the patients complain of defective vision which is more for near than distance and is associated with asthenopic symptoms due to sustained accommodative efforts.

4. 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.

Signs

1. Size of eyeball may appear small as a whole.

2. Cornea may be slightly smaller than the normal.

3. Anterior chamber is comparatively shallow.

4. Fundus examination reveals a small optic disc which may look more vascular with ill-defined margins and even may 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).

5. A-scan ultrasonography (biometry) may reveal a short antero-posterior length of the eyeball.

Complications

If hypermetropia is not corrected for a long time the following complications may occur:

1. Recurrent styes, blepharitis or chalazia may occur, probably due to infection introduced by repeated rubbing of the eyes, which is often done to get relief from fatigue and tiredness.

2. Accommodative convergent squint may develop in children (usually by the age of 2-3 years) due to excessive use of accommodation.

3. Amblyopia may develop in some cases.

It may be anisometropic, strabismic or ametropic.

4. 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.