COT Tonometry and Keratometry 5 — Questions and Answers
Question 1: Which type of tonometer is most appropriate for an uncooperative child or a patient who cannot be positioned at a slit lamp?
- Goldmann applanation tonometer
- Non-contact tonometer
- Rebound (iCare) tonometer (Correct answer)
- Perkins tonometer only
Correct answer: Rebound (iCare) tonometer
Rebound tonometers like the iCare require no anesthetic, minimal cooperation, and can be used handheld in any position.
Question 2: The refractive index assumed by most manual keratometers when converting radius of curvature to diopters is approximately:
- 1.336
- 1.3375 (Correct answer)
- 1.376
- 1.000
Correct answer: 1.3375
Most manual keratometers use a standardized keratometric refractive index of 1.3375 to convert corneal radius to diopters.
Question 3: What is diurnal variation of IOP, and when is IOP typically highest?
- IOP fluctuates with meals; highest after eating
- IOP varies throughout the day; typically highest in the early morning (Correct answer)
- IOP varies with ambient light; highest at noon
- IOP fluctuates with blinking rate; highest at bedtime
Correct answer: IOP varies throughout the day; typically highest in the early morning
IOP follows a circadian rhythm and is typically highest in the early morning hours, which can be clinically significant for glaucoma monitoring.
Question 4: When performing keratometry on a patient with dry eye, the technician observes mires breaking up quickly. The BEST approach is to:
- Record the reading from the broken mires as an average
- Instill artificial tears, wait briefly, then reattempt measurement (Correct answer)
- Dilate the patient before keratometry
- Increase the keratometer's illumination to compensate
Correct answer: Instill artificial tears, wait briefly, then reattempt measurement
A dry, irregular tear film disrupts the reflected mires; lubricating drops temporarily stabilize the tear film for a more accurate reading.
Question 5: Which statement about the Perkins tonometer is TRUE?
- It uses an air puff and requires no patient contact
- It is a hand-held version of Goldmann applanation tonometry (Correct answer)
- It measures IOP by corneal indentation depth
- It is only used under general anesthesia
Correct answer: It is a hand-held version of Goldmann applanation tonometry
The Perkins tonometer is a hand-held applanation device that uses the same Goldmann applanation principle, useful for supine or pediatric patients.
Question 6: When recording keratometry results, 43.50 D @ 180° / 45.00 D @ 90° represents a cornea with:
- 1.50 D of with-the-rule astigmatism (Correct answer)
- 1.50 D of against-the-rule astigmatism
- 1.50 D of oblique astigmatism
- No astigmatism because both values are normal
Correct answer: 1.50 D of with-the-rule astigmatism
With-the-rule astigmatism means the steeper meridian is near 90°; here 45.00 D @ 90° is steeper, giving 1.50 D WTR astigmatism.
Question 7: Which medication instilled before tonometry can falsely lower IOP measurements by reducing aqueous production during the exam?
- Topical fluorescein
- Topical anesthetic (proparacaine)
- Topical beta-blocker (timolol) (Correct answer)
- Topical cycloplegic (cyclopentolate)
Correct answer: Topical beta-blocker (timolol)
Topical beta-blockers like timolol reduce aqueous production and can lower IOP, potentially affecting the accuracy of a baseline pressure reading.
COT Tonometry and Keratometry 5
Which type of tonometer is most appropriate for an uncooperative child or a patient who cannot be positioned at a slit lamp?