COA - Certified Ophthalmic Assistant Tonometry and Glaucoma Questions and Answers 1 — Questions and Answers
Question 1: A patient's intraocular pressure (IOP) measures 28 mmHg via Goldmann applanation tonometry. Pachymetry reveals a central corneal thickness of 610 µm. How does the corneal thickness likely affect this IOP reading?
- The true IOP is likely lower than 28 mmHg. (Correct answer)
- The true IOP is likely higher than 28 mmHg.
- Corneal thickness does not affect Goldmann tonometry readings.
- The IOP reading is artificially lowered by the thick cornea.
Correct answer: The true IOP is likely lower than 28 mmHg.
Goldmann tonometry is calibrated for an average central corneal thickness of about 520-540 µm. A thicker-than-average cornea provides more resistance to the tonometer probe, resulting in a falsely high IOP reading. Conversely, a thinner cornea would lead to a falsely low reading.
Question 2: Which of the following is considered the 'gold standard' for measuring intraocular pressure?
- Schiotz tonometry
- Goldmann applanation tonometry (Correct answer)
- Non-contact tonometry (NCT)
- Digital palpation
Correct answer: Goldmann applanation tonometry
Goldmann applanation tonometry (GAT) is widely considered the international gold standard for measuring intraocular pressure due to its accuracy and reproducibility. It works by measuring the force required to flatten a specific area of the cornea.
Question 3: A patient presents with a sudden onset of severe eye pain, nausea, blurred vision, and halos around lights. Tonometry reveals a very high IOP. Which type of glaucoma is most likely responsible for these symptoms?
- Primary open-angle glaucoma
- Normal-tension glaucoma
- Acute angle-closure glaucoma (Correct answer)
- Traumatic glaucoma
Correct answer: Acute angle-closure glaucoma
Acute angle-closure glaucoma is a medical emergency characterized by a sudden blockage of the eye's drainage angle, leading to a rapid and severe spike in intraocular pressure. This causes symptoms like intense eye pain, redness, blurred vision, halos, headache, and nausea. Primary open-angle glaucoma, the most common form, is typically painless and develops slowly.
Question 4: During Goldmann applanation tonometry, the fluorescein mires are observed to be very thick and wide. This is most likely to cause what type of error in the IOP measurement?
- No error, as mire thickness is irrelevant
- A falsely low reading
- A falsely high reading (Correct answer)
- An intermittent reading
Correct answer: A falsely high reading
Excessive fluorescein in the tear film creates thick mires. The width of the mire band adds to the area of applanation, meaning less force is required from the tonometer dial to align the inner edges. This leads the operator to record a pressure that is falsely high. Conversely, too little fluorescein (thin mires) can lead to a falsely low reading.
Question 5: What is the generally accepted range for normal intraocular pressure (IOP) in the adult population?
- 5-10 mmHg
- 22-30 mmHg
- 3-7 mmHg
- 10-21 mmHg (Correct answer)
Correct answer: 10-21 mmHg
The statistically normal range for intraocular pressure in adults is typically between 10 and 21 millimeters of mercury (mmHg). Pressures consistently above 21 mmHg are considered ocular hypertension and increase the risk for developing glaucoma, although glaucoma can also develop at pressures within the normal range (normal-tension glaucoma).
Question 6: Which of the following is a key principle of applanation tonometry, based on the Imbert-Fick law?
- Measuring the depth of indentation on the sclera
- Calculating the rebound speed of a probe from the cornea
- Measuring the force required to flatten a specific area of the cornea (Correct answer)
- Analyzing the corneal shape change in response to a puff of air
Correct answer: Measuring the force required to flatten a specific area of the cornea
The Imbert-Fick principle, on which Goldmann applanation tonometry is based, states that the pressure inside an ideal sphere is equal to the force necessary to flatten its surface divided by the area of flattening (P = F/A). Therefore, the tonometer measures the external force required to flatten a 3.06 mm diameter area of the central cornea to calculate the internal pressure.
COA - Certified Ophthalmic Assistant Tonometry and Glaucoma Questions and Answers 1
A patient's intraocular pressure (IOP) measures 28 mmHg via Goldmann applanation tonometry.
Pachymetry reveals a central corneal thickness of 610 µm.
How does the corneal thickness likely affect this IOP reading?