Fincham’s test differentiates cataract from
**Core Concept**
Fincham's test is a clinical examination technique used to differentiate between cataracts and corneal opacities. It relies on the fact that a cataractous lens can still refract light and cause a change in the patient's vision, whereas a corneal opacity cannot.
**Why the Correct Answer is Right**
In Fincham's test, a patient is asked to read a near vision card through a pinhole in a dark room. If the patient can read the card clearly, it suggests that the opacity is in the cornea, as the pinhole only allows light to enter through a small, central area, bypassing the opacity. However, if the patient cannot read the card clearly, it indicates a cataractous lens, as the light is being refracted by the cataractous lens. This is because the cataractous lens can still bend (refract) light, causing the patient to see a distorted image.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Fincham's test is specifically designed to differentiate between cataracts and corneal opacities, not other types of opacities such as vitreous or retinal opacities.
**Option B:** This option is incorrect because Fincham's test relies on the patient's ability to read a near vision card through a pinhole, which is not relevant to the differentiation between cataracts and other conditions such as age-related macular degeneration.
**Clinical Pearl / High-Yield Fact**
Fincham's test is a classic example of a clinical examination technique that relies on the use of a pinhole to bypass a corneal opacity and assess the patient's visual acuity through a clear central area. This technique is particularly useful in differentiating between cataracts and corneal opacities.
**Correct Answer: C. Corneal opacity**