Tonometry and Keratometry Flashcards
6 cards from real COA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Tonometry and Keratometry flashcards as text
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?
Answer: Align the prism so the red line is on the axis of the minus cylinder.
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.
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?
Answer: A poor tear film or dry eye.
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.
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)?
Answer: The feeler arm should fall toward the patient.
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.
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?
Answer: It may cause an artificially high IOP reading.
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.
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?
Answer: Corneal astigmatism
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.
Which of the following scenarios would MOST likely lead to an inaccurate intraocular pressure reading when using a non-contact tonometer (NCT)?
Answer: The patient is squeezing their eyelids tightly.
Squeezing the eyelids (the Valsalva maneuver) increases external pressure on the globe, which can artificially elevate the intraocular pressure reading. This is a common source of error in all forms of tonometry, including non-contact tonometry. The other factors listed are less likely to have a significant impact on an NCT reading.