**Core Concept**
The Van Herick method is a technique used to estimate the depth of the anterior chamber in the eye. It involves measuring the angle formed between the cornea and the iris at the nasal and temporal aspects. The grading system is based on this angle, with '1' being the narrowest and '4' being the widest.

**Why the Correct Answer is Right**
A Van Herick angle grade '3' indicates that the angle formed between the cornea and the iris is approximately 1/4 of the corneal thickness. This corresponds to a moderate reduction in the anterior chamber depth. In clinical practice, a Van Herick angle grade '3' is often associated with glaucoma suspects or patients with a history of ocular hypertension. The reduction in anterior chamber depth can increase the risk of angle closure glaucoma.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide any information about the Van Herick angle grading system.
**Option B:** This option is incorrect because it does not accurately describe the implications of a Van Herick angle grade '3'.
**Option C:** This option is incorrect because it does not provide a clear description of the Van Herick angle grading system.

**Clinical Pearl / High-Yield Fact**
The Van Herick method is a quick and simple way to estimate the anterior chamber depth, but it should not be used as the sole diagnostic criterion for glaucoma. A comprehensive eye examination, including gonioscopy and tonometry, is essential for accurate diagnosis and management.

**Correct Answer: D.**