**Question:** Uniocular polyopia is seen in which stage of cataract –

A. Nuclear cataract
B. Cortical cataract
C. Posterior subcapsular cataract
D. Mixed cataract

**Core Concept:**
Uniocular polyopia, also known as heterophoria or heterotropia, is a condition characterized by the involuntary movement of one eye inward or outward to counteract the straight ahead position of the other eye. This occurs due to the presence of a cataract in one eye, which affects binocular vision and depth perception. Cataracts are a clouding of the lens within the eye that can lead to vision impairment.

**Why the Correct Answer is Right:**
Cataract can occur in various stages, including nuclear, cortical, posterior subcapsular, and mixed. In uniocular polyopia, the affected eye has a cataract that is primarily located in the lens nucleus (A). When the nucleus is affected, the lens becomes denser, leading to a decrease in the eye's ability to focus light properly. This causes the eye to involuntarily move to compensate for the defocused vision, resulting in uniocular polyopia.

**Why Each Wrong Option is Incorrect:**
- Nuclear cataract (B): Although nuclear cataract can lead to uniocular polyopia, the correct answer is the nucleus, not the entire lens.
- Cortical cataract (C): A cortical cataract affects the lens cortex, not the nucleus, and thus is not the correct answer for uniocular polyopia.
- Posterior subcapsular cataract (D): A posterior subcapsular cataract affects the lens posterior subcapsular region, not the nucleus, making it an incorrect answer for uniocular polyopia.
- Mixed cataract (D): A mixed cataract involves both nuclear and cortical changes, not solely affecting the nucleus, making it an incorrect answer for uniocular polyopia.

**Clinical Pearl:**
Uniocular polyopia is a visual manifestation that occurs due to the presence of a cataract in one eye, particularly one affecting the nucleus. This condition presents a challenge for patients, as they may experience double vision and difficulties in performing activities that require binocular vision, such as reading or driving. Early diagnosis and treatment of cataracts can prevent the development of uniocular polyopia and preserve binocular vision and depth perception.