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

A. Pressure within the eyeball
B. Relaxation of the iris
C. Degree of anterior chamber angle narrowing
D. Dilation of the pupil

**Core Concept:** Tonography is a non-invasive technique used to assess the pressure within the eye, specifically the intraocular pressure (IOP). IOP is crucial for diagnosing and monitoring glaucoma, a group of eye disorders characterized by progressive optic nerve damage and vision loss.

**Why the Correct Answer is Right:** In tonography, a sterile, transparent fluid, usually air, is injected into the anterior chamber of the eye through a small incision in the cornea. The pressure applied by the fluid causes the eye to expand and the cornea to change shape. This change in shape is then measured and used to calculate the intraocular pressure.

**Why Each Wrong Option is Incorrect:**

A. Tonography does not measure pressure directly; it estimates it based on corneal deformation. Thus, option A is incorrect.

B. Relaxation of the iris is irrelevant to the tonography process, as tonography assesses IOP independently of iris status. So, option B is incorrect.

C. Tonography evaluates corneal deformation, not the degree of anterior chamber angle narrowing. Therefore, option C is incorrect.

D. Dilation of the pupil is a side effect of tonography but not a direct result of the technique. Thus, option D is incorrect.

**Clinical Pearl:** Tonography is a valuable tool for assessing IOP in patients with certain eye conditions that make traditional Goldmann applanation tonometry challenging or impossible. Examples include corneal edema, corneal grafts, or corneal diseases that affect corneal transparency, as these conditions can impede accurate tonometry measurements. In such cases, tonography can provide a reliable alternative for diagnosing and monitoring glaucoma.