One type of defective eye sight was blurred if you look at distance objects.
Cause: The eye ball is too thick
Can be overcome by using a concave lens glasses (-)
Unable to see the difference at close range
Cause: The eye ball is too flat
Can be overcome by using glasses lansa convex (+)
Defective eye can not see the object distance or close to clear.
The cause is the age factor
Can be overcome with double glasses
Eye defect that causes a person can not observe the lines of horizontal and vertical with the clear and bright
The cause is not shaped corneas, and sliced eyeball more curved in one area thananother.
Can be overcome by using a cylindrical lens