FREE COA Tonometry and Keratometry Questions and Answers

Question 1

A patient with high, against-the-rule astigmatism requires an intraocular pressure check using Goldmann applanation tonometry. To obtain an accurate measurement, how should the ophthalmic assistant orient the tonometer prism?

Accepted Answer

Align the prism so the red line is on the axis of the minus cylinder.

Answer

For patients with corneal astigmatism greater than 3.00 diopters, the flattened area of the cornea becomes elliptical, which can lead to an inaccurate IOP reading. To compensate, the Goldmann tonometer prism should be rotated so that the red line on the prism is aligned with the patient's minus cylinder axis.

Question 2

When performing manual keratometry, the ophthalmic assistant is unable to get clear, stable mire images, and they appear to be pulsating or jumping. This finding is most indicative of which of the following?

Accepted Answer

A poor tear film or dry eye.

Answer

Unstable, distorted, or pulsating mires during keratometry are often a sign of an inadequate tear film or significant dry eye, as the mires are reflected off the tear layer covering the cornea. Asking the patient to blink can often temporarily resolve this issue and allow for a more accurate measurement.

Question 3

An ophthalmic assistant is checking the calibration of a Goldmann tonometer using the supplied calibration bar. At the '0' setting, what should happen when the dial is turned slightly forward (e.g., to +0.05)?

Accepted Answer

The feeler arm should fall toward the patient.

Answer

To verify the calibration of a Goldmann tonometer at the 0 position, the feeler arm should move freely. When the dial is turned slightly forward (clockwise, toward a positive value), the arm should fall away from the examiner and toward the patient. If it moves toward the examiner or doesn't move, it indicates an inaccuracy.

Question 4

A patient's intraocular pressure is measured as 25 mmHg with applanation tonometry. However, a pachymetry reading reveals a central corneal thickness of 610 microns. How does this corneal thickness likely affect the IOP measurement?

Accepted Answer

It may cause an artificially high IOP reading.

Answer

Goldmann applanation tonometry is calibrated for an average central corneal thickness (CCT) of around 520-545 microns. A thicker cornea is more rigid and requires more force to flatten, which can result in an artificially high intraocular pressure reading. Conversely, a thinner cornea can lead to an artificially low reading.

Question 5

While performing keratometry, the ophthalmic assistant obtains two different readings: 44.50 D at 180 degrees and 42.00 D at 90 degrees. This difference is used to quantify which of the following?

Accepted Answer

Corneal astigmatism

Answer

Keratometry measures the curvature of the cornea in its two principal meridians. A difference between these two measurements (K-readings) indicates that the cornea is not perfectly spherical. This difference is the amount of corneal astigmatism.

COA - Certified Ophthalmic Assistant Practice Test

COA - Certified Ophthalmic Assistant Practice Test

FREE COA Tonometry and Keratometry Questions and Answers