COT Tonometry and Keratometry 2 — Questions and Answers
Question 1: Which tonometry method uses a variable force to flatten a fixed area of cornea (3.06 mm diameter)?
- Non-contact tonometry
- Goldmann applanation tonometry (Correct answer)
- Tono-Pen tonometry
- Rebound tonometry
Correct answer: Goldmann applanation tonometry
Goldmann applanation tonometry flattens a fixed 3.06 mm diameter corneal area and varies the force to achieve that area.
Question 2: What fluorescein pattern indicates the correct endpoint during Goldmann applanation tonometry?
- Two complete blue circles just touching
- Two semicircles whose inner edges just touch (Correct answer)
- A single bright green ring
- Overlapping yellow mires
Correct answer: Two semicircles whose inner edges just touch
The correct endpoint is when the inner edges of the two fluorescein-stained semicircles just touch each other.
Question 3: A patient has a central corneal thickness of 620 µm. How does this affect Goldmann IOP readings compared to a 545 µm cornea?
- IOP reading is falsely low
- IOP reading is falsely high (Correct answer)
- IOP reading is unaffected
- IOP reading is accurate only with correction tables
Correct answer: IOP reading is falsely high
Thicker corneas resist applanation more, causing the Goldmann tonometer to overestimate true IOP.
Question 4: During keratometry, what does the technician measure when aligning the plus (+) and minus (−) mires?
- The axial length of the eye
- The radius of curvature of the anterior cornea in two principal meridians (Correct answer)
- The depth of the anterior chamber
- The refractive index of the tear film
Correct answer: The radius of curvature of the anterior cornea in two principal meridians
Keratometry measures the radius of curvature of the anterior corneal surface in the flattest and steepest meridians.
Question 5: A keratometry reading of 44.00 D @ 90° / 46.00 D @ 180° indicates:
- Against-the-rule astigmatism (Correct answer)
- With-the-rule astigmatism
- Oblique astigmatism
- No clinically significant astigmatism
Correct answer: Against-the-rule astigmatism
Against-the-rule astigmatism exists when the steeper meridian is closer to horizontal (180°), meaning more power at 180° than 90°.
Question 6: Which of the following would cause a falsely LOW IOP reading with non-contact (air-puff) tonometry?
- Patient squeezing lids tightly
- Edematous (waterlogged) cornea
- Excessive fluorescein instillation
- Patient looking slightly downward (Correct answer)
Correct answer: Patient looking slightly downward
When the patient looks slightly downward, the air puff strikes the peripheral rather than central cornea, yielding an artificially low reading.
Question 7: The Tono-Pen tonometer is especially useful for which clinical situation?
- Screening large groups quickly without contact
- Measuring IOP through a bandage contact lens or irregular cornea (Correct answer)
- Evaluating corneal topography simultaneously
- Performing tonometry under general anesthesia only
Correct answer: Measuring IOP through a bandage contact lens or irregular cornea
The Tono-Pen's small tip makes it ideal for measuring IOP through bandage contact lenses or on irregular corneal surfaces.
COT Tonometry and Keratometry 2
Which tonometry method uses a variable force to flatten a fixed area of cornea (3.06 mm diameter)?