Page 3 - NAME OF CONDITION: REFRACTIVE ERRORS

NAME OF CONDITION: REFRACTIVE ERRORS

I. WHEN TO SUSPECT/ RECOGNIZE?

a) Introduction:

An easily detectable and correctable condition like refractive errors still remains a
significant cause of avoidable visual disability in our world. A child, whose refractive
error is corrected by a simple pair of spectacles, stands to benefit much more than an
operated patient of senile cataract – in terms of years of good vision enjoyed and in
terms of overall personality development. In developing countries, like India, it is
estimated to be the second largest cause of treatable blindness, next only to cataract.
Measurement of the refractive error is just one part of the whole issue. The most
important issue however would be to see whether a remedial measure is being made

available to the patient in an affordable and accessible manner, so that the disability is
corrected. Because of the increasing realization of the enormous need for helping
patients with refractive error worldwide, this condition has been considered one of
the priorities of the recently launched global initiative for the elimination of avoidable
blindness: VISION 2020 – The Right to Sight.

b) Case definition:

i. Myopia or Short sightedness or near sightedness
ii. Hypermetropia or Long sightedness or Far sightedness
iii. Astigmatism
These errors happen because of the following factors:
a. Abnormality in the size of the eyeball – The length of the eyeball is too long in
myopia and too short in hypermetropia.
b. Abnormality in the curvature of the cornea – The curvature of the cornea is too
steep in myopia and too flat in hypermetropia. In addition, irregularity of the
corneal surface may give rise to astigmatism.

c. Abnormality in the refractive index – Light passes through the major refracting
surfaces like the cornea and lens, before impinging on the retina. A high refractive
index may cause myopia, while a low refractive index may cause hypermetropia.

Of all these factors, the abnormality of the size of the eyeball is most common in
producing refractive errors.

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