Vision defects include myopia (nearsightedness), hyperopia (farsightedness), astigmatism, and presbyopia. These conditions result from abnormalities in the eye’s shape or lens flexibility, affecting the ability to focus clearly.
A person is unable to see objects distinctly placed within 75 cm from his eyes. a) Name the defect of vision the person is suffering from. b) List its two possible causes. c) Calculate the power of the lens needed to correct this defect. Assume that the near point for the normal eye is 25 cm.
Share
a) The person is suffering from the defect of vision known as myopia or nearsightedness.
b) Two possible causes of myopia include:
• Excessive elongation of the eyeball: In myopia, the eyeball is too long from front to back, causing light to focus in front of the retina rather than directly on it.
• Increased curvature of the cornea or lens: Sometimes, myopia can be caused by an increased curvature of the cornea or lens, leading to the improper focusing of light.
c) To calculate the power of the lens needed to correct the myopic vision, we can use the lens formula:
Given, u = – 25 cm, v = -75 cm, f = ?
1/f = 1/v – 1/u
F = 37.5
P = 100/f
= + 2.67 D