COA Tonometry and Glaucoma 2

Question 1

Goldmann applanation tonometry (GAT) measures intraocular pressure by determining the force required to flatten a corneal area of what specific diameter?

Accepted Answer

3.06 mm

Answer

The Goldmann tonometer prism flattens a circular corneal area of 3.06 mm diameter. At this diameter, the forces of surface tension and corneal rigidity cancel each other out, providing an accurate IOP reading.

Question 2

A patient's IOP is measured by GAT as 14 mmHg OD and 15 mmHg OS. The COA notes the corneal pachymetry is 490 microns OU. How should the COA interpret this?

Accepted Answer

IOP may be falsely low; thin corneas tend to underestimate true IOP with GAT

Answer

GAT assumes a standard central corneal thickness (CCT) of ~550 microns. Corneas thinner than 550 microns are more easily applanated, requiring less force, causing GAT to underestimate true IOP. A CCT of 490 microns is significantly thin.

Question 3

Which type of glaucoma is characterized by a narrow or closed iridocorneal angle that obstructs aqueous outflow?

Accepted Answer

Angle-closure glaucoma (ACG)

Answer

Angle-closure glaucoma results from apposition or adhesion of the peripheral iris against the trabecular meshwork, blocking aqueous humor outflow through the iridocorneal angle and causing IOP elevation.

Question 4

What is the recommended first step before performing Goldmann applanation tonometry?

Accepted Answer

Instill a topical anesthetic and fluorescein

Answer

GAT requires topical anesthesia for patient comfort and fluorescein sodium to create the characteristic tear film meniscus rings that enable proper mire alignment. Both are instilled before the procedure.

Question 5

The optic nerve cup-to-disc ratio (CDR) is evaluated during ophthalmic assessment. Which CDR value is MOST suggestive of glaucomatous optic nerve change?

Accepted Answer

0.8 OD with inferior rim thinning

Answer

A CDR of 0.8 is large and, combined with inferior rim thinning (loss of the ISNT rule pattern), is highly suspicious for glaucomatous optic neuropathy. Both the ratio and the rim quality must be assessed.

COA - Certified Ophthalmic Assistant Practice Test

COA - Certified Ophthalmic Assistant Practice Test

COA Tonometry and Glaucoma 2