Applanation Tonometry

Question 1

Which three are applanation tonometry?

A. Goldmann
B. Perkins
C. Non-contact
D. Schiotz

Answer 1

A. Goldmann
B. Perkins
C. Non-contact

Schiotz is indentation tonometry

Question 2

What is the Imbert-Fick formula?

Answer 2

Pressure = Force / Area

Question 3

What are three assumptions of the Imbert-Fick law about the cornea and the actual condition

Answer 3

1) Cornea is infinitely thin (is approximately 550 microns)
2) Perfectly elastic and flexible (membrane has resistance)
3 Is Dry (Cornea has tear film)

Question 4

What does corneal thickness & rigidity cause the measured pressure to be relative to the true pressure?

What does surface tension cause the measured pressure to be relative to the true pressure?

Answer 4

• Corneal thickness & rigidity cause measure pressure to be HIGHER than true pressure
• Corneal surface tension cause measure pressure to be LOWER than true pressure`

Question 5

What are three assumptions about Goldmann Tonometry (Diameter of area applanated, Volume displaced and Corneal thickness)

Answer 5

• Diameter of area applanated = 3.06 mm
• Volume displaced is 0.5 mm3
• Corneal thickness 520 microns

Question 6

What is the purpose of Sodium fluorescein dye? (for tonometry and SLE)

Answer 6

• Defines mire pattern during tonometry

- Vital Dye stain (dye penetrates and cell-cell break)

Question 7

What is the SLE setup for Vital Dye staining? (Filter, Mag, Parallelpipe width, Rheostat intensity)

Answer 7

• Cobalt blue filter
• Medium mag 10-16x
• Wide parallelpiped
• High intensity rheostat

Question 8

How should the Tonometry probe be oriented (what angle) and when would it need to be realigned?

Answer 8

• 180 degress at the white hashmark

- realigned if CORNEAL astigmatism > 3D

Question 9

For tonometry probe disinfection, what viruses do alcohol wipes NOT remove?

Answer 9

• Alcohol wipes do not remove Hep C or Hep B

Question 10

What is the SLE setup for Goldmann? (Mag, Beam width, height, Angle, Filters, Rheostat)

Answer 10

• 6.3-10x, Max beam width and height, Max rheostat, illumination arm 45-60 degrees, No 10% grey filter, Cobalt filter

Question 11

What is the average IOP range and range outside normal IOP limits?

Answer 11

10-21 mmHg average range
< 6-8 mmHg, > 22 mmHg outside normal limit
Assymetry >= 3mmHg between each eye