Flashcards · Biology · The Nervous System
Eye Defects and Their Correction
-
What is short-sightedness?
A defect where distant objects look blurred, because light focuses in front of the retina.
-
What is long-sightedness?
A defect where near objects look blurred, because light would focus behind the retina.
-
What causes short sight?
An eyeball that is too long, or a lens that bends light too much.
-
What causes long sight?
An eyeball that is too short, or a lens that bends light too little.
-
Which lens corrects short sight?
A concave lens.
-
Which lens corrects long sight?
A convex lens.
-
What does a concave lens do to light rays?
It spreads them out (diverges them).
-
What does a convex lens do to light rays?
It brings them together (converges them).
-
What is a cataract?
A cloudy area in the lens, which makes vision misty or blurred.
-
How is a cataract treated?
The cloudy lens is replaced with a clear artificial lens by surgery.
-
What causes colour blindness?
Missing or faulty cone cells for one or more of the colours.
-
Why is colour blindness more common in men?
The genes for the cone cells are on the X chromosome, and men have only one.
-
Can colour blindness be cured?
No. It is inherited, though tinted lenses can help some people.
-
Name one other way to correct short sight apart from glasses.
Contact lenses or laser eye surgery.
-
Why do many people become long-sighted as they get older?
The lens becomes stiffer and cannot get thick enough to focus on near objects.
-
Which common mistake do students make about the retina?
Saying the light is focused "on the cornea". It must be focused on the retina.