In old age, the vision of the eye becomes dim. It is due to:
a. Myopia
b. Hypermetropia
c. Cataract
d. Astigmatism

Hint: Cataract is a dense, cloudy area that forms in the lens of the eye. We say it is cataract when proteins in the eye form clumps that prevent the lens from transmitting clear images to the retina. Cataract is said to cause opacification of the lens of the eyes. There is accumulation of yellow-brown pigment in the lens. Cataracts could be of several types.

Complete answer:
Cataracts are common in old age people. In this condition the sight is impaired due to the lens becoming opaque (safed motia) due to white membrane formed as a result of protein denaturation.

Symptoms of cataracts include-
• Blurry vision
• Trouble seeing at night
• Seeing colors as faded
• Increased sensitivity to glare
• Double vision in the affected eye

Causes of cataracts:
• An overproduction of oxidants
• Smoking
• Ultraviolet radiation
• Long-term use of steroids and other medications
• Diseases like diabetes
• Trauma
• Radiation therapy

Iris is the coloured portion of the eyes behind which the lenses are present, where cataract forms. Clear and sharp images are formed on the retina when the lens focuses the light that passes into our eyes. With enhancing age, the flexibility and transparency of the eye lens decreases and the thickness of the lenses in our eyes increases. Age-related and some of the other medical conditions cause tissues within the lens to break down and clump together, clouding small areas within the lens. As the cataract continues to develop, the clouding becomes denser and involves a bigger part of the lens. A cataract scatters and blocks the light as it passes through the lens, thus, preventing a sharply defined image from reaching the retina.

Hence, the correct answer is option (C).

Note: Cure for cataract:
Surgery is preferred to cure cataract. The defective lens is replaced with a clear artificial lens.
Types of cataracts:
• Subcapsular cataract: At the back of the lens. It is generally in patients with diabetes or the ones who take high doses of steroid medications.
• Nuclear Cataract: It forms inside the nucleus of the lens of the eye. It is usually seen in aged people.
• Cortical Cataract: This type occurs in the cortex of the lens which surrounds the nucleus.