QS Study

Refractive error of Eyeball

Refractive error means that the form of your eye does not bend light properly, resulting in an unclear image which is sometimes so severe that it causes visual impairment. The length of the eyeball, changes in the nature of the cornea, or aging of the lens can cause refractive errors.

Refractive errors of eye are – (a) Myopia, (b) Hypermetropia, (c) Astigmatism, and (d) Presbiopia.

MYOPIA (close objects are clear, and distant objects are blurry):

In this case, a person cannot see the distant objects easily but the person can see the near object without difficulty. Parallel rays of light coming from the distant objects to caused in front of the retina. It occurs at the young age and often progresses when the body is growing rapidly.

Causes:

  • ↑anteroposterior diameter of the eyeball.
  • ↑Curvature of a lens.

Correction: corrected by using a concave lens with suitable diopters.

Fig: Refractive error of Eyeball

HYPER METROPIA (close objects are more blurry than distant objects):

In this condition, a patient cannot see the near objects but can see the distant object without difficulty. An eyeball is shorter than normal. In mild hyperopia, distance vision is clear while near vision is blurry. Parallel light rays coming from the near objects focused behind the retina. It normally occurs in old age.

Causes:

  • ↓ Anteroposterior diameter of an eyeball.
  • ↓ Focusing power of the lens.

Correction: Corrected by using a convex (converging) lens with suitable diopters.

ASTIGMATISM:

Here the curvature of the lens and cornea are not uniform. Thus it gives the different digresses of refraction in different planes. So, the image is in focus in some planes and spread over a diffuse area. This abnormality may result in vision that is much like looking into a distorted, wavy mirror.

  • Causes: the unequal curvature of an eyeball.
  • Correction: Corrected by using a cylindrical or contact lens.

PRESBYOPIA (aging of the lens in the eye):

A defect of vision in advancing age involving loss of accommodation or recession of near point due to loss of elasticity of crystalline lens. It usually occurs in 40 to 45 years of age

  • Cause: Loss of elasticity of crystalline lens.
  • Correction: corrected by using the convex lens.
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