**Question:** Tonography helps you to determine –

A. Pressure in the eye
B. Iris diameter
C. Corneal thickness
D. Anterior chamber depth

**Core Concept:** Tonography is a non-invasive technique used to assess the pressure within the eye, particularly in the anterior chamber. It is a valuable tool in diagnosing glaucoma and monitoring treatment response.

**Why the Correct Answer is Right:** Tonography measures the pressure inside the eye by assessing the deformation of the eye's anterior chamber upon application of a small air pulse. The resulting deformation is then converted into pressure values. In this case, the correct answer is **A. Pressure in the eye** because tonography directly measures the pressure within the eye, specifically the anterior chamber.

**Why Each Wrong Option is Incorrect:**

B. **Iris diameter (B)**: Iris diameter is related to the size of the eye but does not directly provide information about the intraocular pressure, making it an incorrect answer.

C. **Corneal thickness (C)**: Corneal thickness is a measure of the cornea and not related to the intraocular pressure directly, making it an incorrect answer.

D. **Anterior chamber depth (D)**: Anterior chamber depth is related to the size of the eye but does not directly provide information about the intraocular pressure, making it an incorrect answer.

**Clinical Pearl:** Tonography is a crucial diagnostic tool in ophthalmology, particularly for detecting early stages of glaucoma and monitoring treatment response. Early detection and proper management of glaucoma are essential to prevent irreversible optic nerve damage and vision loss.