COT Tonometry and Keratometry 3 — Questions and Answers
Question 1: Before performing Goldmann applanation tonometry, which topical agent combination is typically instilled?
- Proparacaine and rose bengal
- Fluorescein and a topical anesthetic (Correct answer)
- Cyclopentolate and phenylephrine
- Tropicamide and pilocarpine
Correct answer: Fluorescein and a topical anesthetic
Fluorescein stains the tear film to visualize the mires, and a topical anesthetic prevents reflex blinking and discomfort.
Question 2: In manual keratometry, irregular mire images (distorted or blurred rings) most commonly indicate:
- Instrument calibration error
- Corneal irregularity such as keratoconus or scarring (Correct answer)
- Incorrect working distance
- Patient accommodating during measurement
Correct answer: Corneal irregularity such as keratoconus or scarring
Distorted or irregular mire reflections indicate an irregular corneal surface, which warrants further evaluation with corneal topography.
Question 3: What is the purpose of the biprism in a Goldmann applanation tonometer?
- To illuminate the cornea with blue light
- To split the fluorescein image into two semicircles for endpoint detection (Correct answer)
- To measure the diameter of the applanated area
- To filter ultraviolet wavelengths from the slit lamp
Correct answer: To split the fluorescein image into two semicircles for endpoint detection
The biprism splits the circular fluorescein ring into two semicircles that the examiner aligns to determine the applanation endpoint.
Question 4: Rebound tonometry (iCare) works on which principle?
- Applanation of a fixed corneal area with a variable weight
- Measurement of indentation depth under a constant load
- Induction and rebound of a small probe that contacts the cornea momentarily (Correct answer)
- Air puff deflection timed by an infrared sensor
Correct answer: Induction and rebound of a small probe that contacts the cornea momentarily
Rebound tonometry fires a small magnetized probe that briefly contacts the cornea; the deceleration and rebound speed are used to calculate IOP.
Question 5: When calibrating a Goldmann tonometer, the check weight is applied and the drum is set to 2 g. What result indicates the instrument is correctly calibrated?
- The mires move apart and then reconverge
- The balance arm swings freely to the up-stop (Correct answer)
- The balance arm remains stationary in the middle position
- The balance arm deflects to the down-stop
Correct answer: The balance arm swings freely to the up-stop
Correct calibration at the 2 g check weight causes the balance arm to swing to the up-stop, confirming the spring tension is accurate.
Question 6: Which factor does NOT directly affect keratometry readings?
- Anterior corneal curvature
- Tear film quality
- Instrument alignment and focus
- Axial length of the eye (Correct answer)
Correct answer: Axial length of the eye
Keratometry measures anterior corneal curvature; axial length is measured separately by A-scan biometry.
Question 7: A patient reports previous radial keratotomy (RK). Which tonometry method is LEAST affected by the altered corneal biomechanics after RK?
- Goldmann applanation tonometry
- Non-contact tonometry
- Dynamic Contour Tonometry (DCT) (Correct answer)
- Schiotz indentation tonometry
Correct answer: Dynamic Contour Tonometry (DCT)
Dynamic Contour Tonometry measures IOP by matching the contour of the cornea and is less influenced by corneal biomechanics than applanation methods.
COT Tonometry and Keratometry 3
Before performing Goldmann applanation tonometry, which topical agent combination is typically instilled?