Tonometry and Keratometry Flashcards

Which tonometry method uses a variable force to flatten a fixed area of cornea (3.06 mm diameter)?

Answer: Goldmann applanation tonometry

Goldmann applanation tonometry flattens a fixed 3.06 mm diameter corneal area and varies the force to achieve that area.

What fluorescein pattern indicates the correct endpoint during Goldmann applanation tonometry?

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.

A patient has a central corneal thickness of 620 µm. How does this affect Goldmann IOP readings compared to a 545 µm cornea?

Answer: IOP reading is falsely high

Thicker corneas resist applanation more, causing the Goldmann tonometer to overestimate true IOP.

During keratometry, what does the technician measure when aligning the plus (+) and minus (−) mires?

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.

A keratometry reading of 44.00 D @ 90° / 46.00 D @ 180° indicates:

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°.

Which of the following would cause a falsely LOW IOP reading with non-contact (air-puff) tonometry?

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.

The Tono-Pen tonometer is especially useful for which clinical situation?

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.