Refractive Errors

How do we see things? / Principle of image formation

The retina, the innermost structure of the eye, behaves like a projection screen which receives the inverse images and the cerebral centre of the brain redresses (form an erect) the image.

Types of refractive errors:

Emmetropia.

Hyperopia or Farsightedness.

Myopia or Nearsightedness.

Astigmatism.

Presbyopia

Emmetropia(Normal vision):

Emmetropia.>

A condition where no refractive error is presents.

Hyperopia or Farsightesness:

Eyeball is too short.

Clear distance vision but suffer with eyestrain for near work.

Correction by means of spherical plus lenses.

Myopia or Nearsightedness:

Eyeball is too long.

Clear near vision and blurred distant vision, people generally squeeze their eyes to see the distant object>

Correction by means of spherical minus lenses.

Astigmatism:

A point object will not have a point image.

Blurred vision for distance and near.

Generally have eyestrain and headache.

Presbyopia:

Lens begin to lost its elasticity/accommodating capacity.

Difficulty in focusing near object and clear distant vision.

Symptoms begins at the age of forty.

Corrected by means of bifocal/progressive lenses for near and intermediate vision.