Tonometry and Keratometry Flashcards
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Read the first 6 Tonometry and Keratometry flashcards as text
Which physical principle, stating that the pressure inside an ideal sphere equals the force required to flatten a specific area of its surface, forms the basis for Goldmann applanation tonometry?
Answer: Imbert-Fick Law
The Imbert-Fick Law (Pressure = Force/Area) is the fundamental principle used in Goldmann applanation tonometry. It relates the intraocular pressure to the external force needed to flatten a 3.06 mm diameter area of the cornea.
A technician is performing keratometry and notes the mires are clear but appear oval-shaped and will not superimpose into perfect circles. Which of the following is the most likely cause for this observation?
Answer: Significant corneal astigmatism
When significant corneal astigmatism is present, the cornea is shaped more like a football (toric) than a basketball (spherical). This causes the circular mires reflected off the cornea to appear oval, indicating different curvatures in different meridians.
A Goldmann applanation tonometry reading can be falsely lowered by which of the following factors?
Answer: A central cornea that is thinner than average
A central cornea that is thinner than average offers less structural resistance to being flattened by the tonometer prism. This means less force is required to achieve applanation, leading to an artificially low intraocular pressure reading.
A patient's keratometry readings are recorded as 45.00 @ 180 / 43.25 @ 090. How would this corneal astigmatism be classified?
Answer: Against-the-rule astigmatism
Against-the-rule astigmatism is present when the horizontal meridian (180 degrees) is the steepest, meaning it has the higher dioptric power. In this case, 45.00 D at 180 is steeper than 43.25 D at 090.
A technician must measure the IOP of a patient who has a heavily scarred and irregular cornea from a previous injury. Which instrument would provide the most reliable reading in this scenario?
Answer: Tono-Pen or iCare tonometer
The Tono-Pen and iCare rebound tonometer are less affected by corneal irregularity and scarring than applanation or air-puff tonometers. They take multiple small-area readings, which are then averaged, providing a more reliable IOP measurement on compromised corneas.
When performing Goldmann applanation tonometry, what is the correct visual endpoint that indicates an accurate measurement?
Answer: The inner edges of the two fluorescein semi-circles just touch.
The correct measurement endpoint is achieved when the force from the tonometer perfectly balances the patient's IOP. This is visualized at the slit lamp as the inner edges of the two green, semi-circular mires making contact without overlapping.