Page 4 - NAME OF CONDITION: REFRACTIVE ERRORS

Myopia

Myopia is a form of refractive error, wherein parallel rays of light come to a focus in front
of the retina, when the eye is at rest.
It is the commonest cause of refractive error and usually detected in the younger age

group.
It consists of two main types:

Simple myopia: is just a variant of the normal and is not a major problem. Apart from the
refractive error, no anatomical or functional complications of the ocular structures occur.
The progression of myopia, more commonly happens during the growing phase of one’s
life. The maximum growth happens between the ages of 12 and 20 years. Frequent change
of glasses maybe required during these years and the myopic error usually stabilizes after
the age of 20. Hence permanent surgical procedures like laser surgery have to be
performed only after documented stabilization of the myopia.

Pathological (or progressive) myopia: also called as degenerative myopia, as the name
suggests is of a more serious nature a type of severe, progressive nearsightedness
characterized by changes in the fundus of the eye, posterior staphyloma, and deficient
corrected acuity. Refractive error is greater than -8.00 diopters, and axial length is greater

than 32.5 mm. In pathological myopia the retina becomes very thin and is stretched at the
periphery. The peripheral retina is at risk of developing tears or holes.
Hypermetropia

Hypermetropia is a form of refractive error, wherein parallel rays of light come to a focus
behind the retina, when the eye is at rest.

In this condition, the person is unable to see near objects well. The eye tries to focus the
images by increasing the refractive index of the lens (by making it thicker) - the process is
called Accommodation.
Astigmatism

In this condition the eye is unable to form a point focus of light upon the retina. Instead of
a single focal point of the image being formed, there are two foci that are separated by a
distance. Hence the person is unable to see an image clearly in one meridian when he is
focusing on another meridian.

- In regular astigmatism, the refractive power varies successively from one meridian to
the next, and each meridian has a uniform curvature at every point across the entrance
pupil. The meridians of greatest and least power, the so-called principal meridians, are
always located at meridians 90 degrees apart.
- In irregular astigmatism, which can be clinically significant in conditions such as
keratoconus and other corneal ectasias; corneal basement membrane and stromal

dystrophies; corneal scarring; and post-surgical corneas (e.g., following penetrating
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