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:
- Hyperopia or Farsightedness.
- Myopia or Nearsightedness.
- 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.
- A point object will not have a point image.
- Blurred vision for distance and near.
- Generally have eyestrain and headache.
- 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.