In cataract the natural lens becomes cloudy because of change in which of the following ?

Correct — option (1), Protein.

The lens is the clear part of the eye that helps focus light. According to the US National Eye Institute (NEI), from around age 40 the proteins in the lens start to break down and clump together, and the clumps make a cloudy area on the lens — a cataract.

So the change behind the clouding is in the lens protein. The NEI explains the clouding as a protein change, and tear glands are not part of the lens at all.

Light has to pass through the lens to reach the retina. A cloudy lens therefore makes vision cloudy or blurry, and colours can look faded.

The idea to remember: a cataract is lens clouding from clumped proteins, and surgery replaces the clouded lens with an artificial one.

Why the others are wrong

• (2)
  Carbohydrate — Carbohydrate is not the lens component whose change clouds it; the NEI describes the lens proteins breaking down and clumping.

  Blood sugar enters from another side: the NEI lists diabetes among the health problems that raise the risk of cataract. A risk factor is not the same thing as the substance that changes in the lens.

• (3)
  Fat — Fat is not the component whose change causes a cataract; that is protein in the lens.

  Fat does connect to the eye in a different way: vitamin A, a fat-soluble vitamin, is needed for vision in dim light, and its deficiency causes night blindness. That is a nutritional problem, not lens clouding.

• (4)
  Tear glands — Tear glands (lacrimal glands) sit in the eye socket, outside the eyeball, and make the tears that keep the eye's surface moist. They are not part of the lens, so a change in them cannot cloud it.

  Trouble with tears belongs to a different condition, dry eye.

The lens sits behind the iris and focuses light onto the retina. To do that it has to stay transparent, and its transparency depends on its proteins staying in order.

In a cataract, those proteins break down and clump together, forming a cloudy area. The NEI describes this change starting around age 40.

Its list of risk factors is diabetes and certain other health problems, smoking, drinking too much alcohol, a family history of cataracts, an eye injury, eye surgery or radiation treatment on the upper body, a lot of time in the sun, and steroid medicines.

Symptoms the NEI describes include cloudy or blurry vision, faded colours, trouble seeing at night, lights that seem too bright, halos around lights and double vision.

Key facts

• A cataract is a cloudy area in the lens of the eye, the clear part that helps focus light (National Eye Institute).
• The clouding comes from proteins in the lens breaking down and clumping together, a change the NEI says starts around age 40.
• NEI risk factors include diabetes, smoking, heavy drinking, family history, much time in the sun, steroid medicines, and past eye injury, eye surgery or upper-body radiation treatment.
• Cataract surgery removes the clouded lens and replaces it with an artificial intraocular lens (IOL).
• Myopia is corrected with a concave lens and hypermetropia with a convex lens; these are focusing errors, not lens clouding.

Common traps

• A cataract clouds the lens; it is not a refractive error like myopia. Glasses correct focusing errors, while the NEI says surgery that replaces the clouded lens is the only way to get rid of a cataract.
• Diabetes raises the risk of cataract, but it is a risk factor, not the substance that changes. The change the stem asks about is in the lens proteins.
• Glaucoma is a different eye disease, in which the optic nerve is damaged. Do not pair glaucoma with the lens or cataract with the optic nerve.

UnlockIAS will link similar questions from RAS Pre 2023 here once that paper is published on this site.

• practice — not a real PYQ

  In cataract surgery, the clouded natural lens is removed and replaced with –

  • (a)a concave spectacle lens
  • (b)an artificial intraocular lens
  • (c)a donor cornea
  • (d)a contact lens
  Answer(2) — The surgeon removes the clouded lens and puts in an artificial intraocular lens (IOL) inside the eye. Options (1) and (4) sit outside the eye and correct focus, and option (3) replaces the cornea, not the lens.
• practice — not a real PYQ

  Which one of the following eye conditions is correctly matched with the part of the eye it affects ?

  • (a)Cataract – Lens
  • (b)Glaucoma – Lens
  • (c)Cataract – Optic nerve
  • (d)Dry eye – Optic nerve
  Answer(1) — A cataract is clouding of the lens. Option (2) is wrong because glaucoma damages the optic nerve, option (3) swaps the parts, and option (4) is wrong because dry eye concerns tears on the eye's surface.