The diagram given below depicts a defect of the human eye which has been corrected by using a suitable lens. Answer the following questions: The diagram given below depicts a defect of the human eye which has been corrected by using a suitable lens. Answer the following questions:
Mention one cause for the above defect.
Topic: Cause of myopia
Answer
The EYEBALL IS TOO LONG from front to back, so the image is formed in front of the retina. (Also acceptable: the lens is too convex, or the ciliary muscles fail to relax, so the eye bends the light too strongly.)
One cause only, so give one.
Both possible causes amount to the same thing — the eye bends light TOO MUCH, so the focus falls too early.
THE SYMMETRY with hypermetropia makes both defects derivable rather than memorised: MYOPIA — eyeball too LONG or lens too CONVEX — bends light TOO MUCH — image IN FRONT of the retina HYPERMETROPIA — eyeball too SHORT or lens too FLAT — bends light TOO LITTLE — image BEHIND the retina Each is the exact opposite of the other in every respect.