**Core Concept**
Senile cataract is a progressive, age-related opacification of the lens in the eye, leading to vision impairment. The earliest clinical feature is a symptom that patients often report, which is directly related to the optical effects of the lens opacities.

**Why the Correct Answer is Right**
The earliest clinical feature of senile cataract is glare, also known as "haloes around lights." This occurs due to the scattering of light by the lens opacities, which creates a "halo" effect around lights at night. The opacities scatter the longer wavelengths of light (yellow and red) more than the shorter wavelengths (blue and violet), resulting in a blue or white halo. This symptom is often reported by patients with early cataracts, particularly at night when driving or reading.

**Why Each Wrong Option is Incorrect**
**Option B:** Frequent change of glasses is not a direct symptom of senile cataract. While patients may report changes in their vision, this is not the earliest clinical feature of cataract.

**Option C:** Coloured halos can be a symptom of cataract, but they are not the earliest feature. Coloured halos are typically seen in more advanced cataracts, where the opacities are more pronounced.

**Option D:** Uniocular polyopia (seeing multiple images of a single object) can be a symptom of other ocular conditions, such as retinal or vitreous disorders. It is not a characteristic symptom of senile cataract.

**Clinical Pearl / High-Yield Fact**
The earliest clinical feature of senile cataract, glare or haloes around lights, is often reported by patients at night while driving or reading. This symptom is a key clue for clinicians to investigate cataract as a possible cause of vision impairment.

✓ Correct Answer: A. Glare. Glare or haloes around lights.