long sightedness – is the condition of the eye where incoming rays of light reach the retina before they converge into a focused image.
short sightedness-see objects more clearly when they are close to the eye, while distant objects appear blurred or fuzzy.
a) What casues this defect?
short sightedness – The eyeball tends to be long. The distance from the lens to the retina is further than average. Short-sightedness is very common. It tends to run in families. http://www.patient.co.uk/showdoc/23069162/
long sightedness-The exact causes of long-sightedness are not well understood. It is known that the eyeballs of long-sighted people tend to be smaller than average, with less curved corneas. It can also can be passes through families.
http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.Nsf/pages/Eye_problems_long-sightedness?OpenDocument
b) Long Sightedness- have to squint to see clearly, eyes feel uncomfortable after reading & writing, pain or burning in the eyes.
Short Sightedness- Causes distant objects to appear fuzzy and unfocused but nearby objects remain the same.
c) For Long Sightedness-????
For Short Sightedness i propose to use i propose to use thin, concave lenses because the light will meet at a focal point which can be the distant object. Also the thinner the lens, the farther the focal point.