SCIENCE NOTE:

COLOR BLINDNESS

• Due to a shortage of come cells (color receptor cells) on the retina.

• Color blind people cannot see some or all colors.Most of them cannot different between red and green.It cannot be corrected because it's heredity. 

PRESBYOPIA

• Common in old people because the eye lens becomes harder and less elastic.The muscles in the uiliary lose their ability to contract and relax.
• As the result both near and far objects cannot be focused on the retina.
• Corrected by wearing glasses with bifocal lenses.