The Optical System
Do your reading inadequate light. Take a break and relax the eye after long hours
of watching TV or reading books. Take enough vitamin A to prevent
night-blindness.
Diabetic mellitus
The small blood vessels of the retina are damaged and exudates will be leaked
into the light sensitive cells on the yellow spot and the person cannot see.
Cataract
Light cannot pass through because the lens has turned opaque. Usually happens
at old age. Exchange for an artificial lens.
Astigmatism
Uneven curvature of the front of the eye causes uneven bending of light rays and
cannot focus all light rays at the same point of the retina. A blurred and distorted
image results
Glaucoma
The eye is in tension due to it fails to get rid of the excessive fluid in the eye.
Usually happens at old age. It usually causes blindness.
Useful websites:
http://www.nei.nih.gov/health/index.htm
http://www.info.gov.hk/elderly/english/health_infoset.htm