Tonometry Principles and Procedures Flashcards
6 cards from real CPO 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 Principles and Procedures flashcards as text
A patient who recently underwent a vitrectomy with an intravitreal gas bubble is scheduled for tonometry. Which of the following is the most critical consideration when measuring their IOP?
Answer: The IOP can fluctuate dramatically with changes in atmospheric pressure, such as changes in altitude.
Intravitreal gas bubbles expand or contract with changes in atmospheric pressure. An ascent in altitude causes the bubble to expand, which can lead to a significant and dangerous increase in IOP. A descent can cause the bubble to contract. This volatility is a primary concern for patients with gas bubbles.
When performing Goldmann applanation tonometry on a patient with significant corneal scarring, the paraoptometric is most likely to encounter which issue?
Answer: Difficulty achieving clear, well-defined semicircular mires for an accurate measurement.
Corneal scarring creates an irregular surface, which distorts the applanated area and the resulting fluorescein mires. This makes it difficult to properly align the inner edges of the semicircles, leading to unreliable or unobtainable readings with Goldmann tonometry.
A paraoptometric performs a calibration check on a Goldmann tonometer. At the '2' setting (20 mmHg), the feeler arm only begins to move when the dial is turned past 2.4. When turned back, it only moves again when the dial is below 1.6. What is the most likely immediate cause of this inaccuracy?
Answer: An internal mechanism that requires lubrication.
This 'sticking' behavior, where the feeler arm does not move freely at the correct calibration points, is a classic sign that the internal mechanical components of the tonometer are not moving smoothly. The most common reason for this is a lack of lubrication, which can often be resolved by cleaning and lubricating the instrument.
Which of the following tonometry methods is theoretically LEAST affected by corneal biomechanical properties like thickness, rigidity, and curvature?
Answer: Dynamic Contour Tonometry (DCT)
Dynamic Contour Tonometry (DCT) is specifically designed to measure intraocular pressure largely independently of corneal properties. Unlike applanation tonometers that flatten the cornea, DCT uses a sensor tip with a contour-matched shape that rests on the cornea, minimizing its deformation and the influence of its biomechanical properties on the reading.
A patient with nystagmus requires an IOP check. Which type of tonometer would be most challenging to use effectively on this patient?
Answer: Non-contact tonometer
Non-contact tonometry (NCT) requires the patient to remain very still and fixated on a target for the instrument to align properly and deliver the air puff to the central cornea. The constant, involuntary eye movements of nystagmus make achieving this precise alignment extremely difficult, often resulting in error readings or the inability to obtain a measurement at all.
When measuring IOP on a patient who has undergone a penetrating keratoplasty (corneal transplant), what is a common finding when comparing Tono-Pen to Goldmann Applanation Tonometry (GAT)?
Answer: Tono-Pen tends to yield significantly higher IOP readings than GAT, especially at lower pressures.
Studies comparing tonometry methods on post-keratoplasty eyes have shown that the Tono-Pen often overestimates IOP when compared to GAT. This discrepancy can be particularly pronounced in the lower IOP ranges. The altered corneal structure, including scarring and irregular curvature, affects the two instruments differently.