Hypermetropia (hyperopia) 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. The posterior focal point is behind the retina, receives a blurred image.
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.
Symptoms OF Hypermertopia
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.
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.
Treatment
A. Optical treatment. Basic principle of treatment is to prescribe convex (plus) lenses, so that the light rays are brought to focus on the retina.
Fundamental rules for prescribing glasses in hypermetropia include:
1. Total amount of hypermetropia should always be discovered by performing refraction under complete cycloplegia.
2. The spherical correction given should be comfortably acceptable to the patient. However The astigmatism should be fully corrected.
3. Gradually increase the spherical correction at 6 months interval till the patient accepts manifest hypermetropia.
4. In the presence of accommodative convergent squint, full correction should be given at the first sitting.
5. If there is associated amblyopia, full correction with occlusion therapy should be started.
