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Hypermetropia (hyperopia, long-sightedness or far- sightedness) is a form of refractive error in which parallel rays of light coming from infinity are focused behind the light sensitive layer of the retina, when the eye is at rest.
Donders (1864) discusses in his historical review about hypermetropia. Much of the problem was caused by confusion between the effects of presbyopia and hypermetropia on near vision.
Small hypermetropia may be corrected by voluntary accommodation. Even high errors of refraction may be corrected this way, but convex glasses may be required if symptoms are not relieved.
Emmetropia is the condition where the eye has no refractive error and requires no correction for distance vision. Refractive error (ametropia) results when cornea and lens inadequately focus the light rays, resulting in blurred images. The measuring unit for refractive error is dioptre (D), which is defined as the reciprocal of the focal length in meters.
In hypermetropia, the cornea is flatter or the axial length is too short. Therefore, the images do not focus by the time they reach to the retina. For clear vision, a hypermetropic eye must accommodate to increase its lenticular power to bring distant objects in focus on retina. This requires contraction of ciliary muscle, and therefore, far-sighted eye is never at rest and work even harder to see near objects clearly. Hypermetropic corrections add positive focusing power to the eye for clear vision.
Accommodation: The degree of hypermetropia corrected by accommodative effort is known as facultative hypermetropia. Remaining uncorrected hypermetropia is called absolute hypermetropia. Total hypermetropia after abolishing voluntary accommodation is known as manifest hypermetropia (facultative plus absolute). With advancing age, accommodative effort cannot be sustained, and hypermetropia becomes absolute till the effort of accommodation fails to correct any hypermetropia. Thus the facultative hypermetropia becomes abolished and there remains no difference between absolute and manifest hypermetropia.
Some of the hypermetropia is corrected by the inherent tone of the ciliary muscles and this is called latent hypermetropia. The degree of latent hypermetropia is high in young persons and becomes less with advancing age. Complete cycloplegia (paralysis of accommodation) can abolish latent hypermetropia. The refractive error estimated under complete cycloplegia is called total hypermetropia (manifest plus latent).
Symptoms
The symptoms vary depending upon the age of the patient and the severity of refractive error. Patient may be asymptomatic. Small amount of refractive error in young patients is usually corrected by mild accommodative effort, without producing any symptoms.
Symptomatic patients may present with:
When hypermetropia is fully corrected: At times the hypermetropia is fully corrected (thus vision is normal) but due to sustained accommodative efforts the patient develops asthenopic symptoms.
Asthenopia (eyestrain).
Frontal or fronto-temporal headache.
Watering.
Mild aversion to light.
These symptoms worsen as the day progresses and are aggravated by prolonged near work.
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