**Question:** Polychromatic lustre is seen in –

A. Corneal edema
B. Keratitis
C. Corneal dystrophy
D. Corneal transplant

**Core Concept:** Polychromatic lustre is a term used to describe the appearance of the cornea when light is reflected off its surface. Corneal health and transparency are crucial for this reflection to occur accurately.

**Why the Correct Answer is Right:** Polychromatic lustre is predominantly seen in cases of corneal dystrophies. Corneal dystrophies are a group of inherited disorders characterized by the accumulation of abnormal deposits in the cornea, leading to cloudiness and reduced transparency.

**Why Each Wrong Option is Incorrect:**

A. Corneal edema: Corneal edema occurs when the cornea swells due to fluid accumulation, causing a white, opaque appearance. Polychromatic lustre is not present in this condition.

B. Keratitis: Keratitis is an inflammation of the cornea, which may cause symptoms but typically does not affect the polychromatic lustre unless there is significant ulceration or scarring.

C. Corneal transplant: A corneal transplant, or keratoplasty, involves replacing the diseased or damaged cornea with a healthy donor cornea. As a result, the polychromatic lustre would be lost from the transplanted cornea.

**Clinical Pearl / High-Yield Fact:** Polychromatic lustre assessment is crucial in diagnosing corneal diseases, particularly in cases of corneal dystrophies, as it provides valuable information about the corneal transparency and can help differentiate between various corneal conditions. This examination technique is part of a comprehensive corneal evaluation and should be performed alongside other clinical assessments, such as slit-lamp examination and visual acuity measurements, to provide a well-rounded diagnosis.