III. Techniques: Applanation Tonometry - Intraocular Pressure measurement
- Background
- Applanation devices measure the amount of pressure needed to flatten a small portion of the Cornea
- Apply Topical Eye Anesthetic to Cornea before testing
- Goldmann Tonometer
- Slit-lamp based device that offers most accurate Intraocular Pressure measurement
- Portable electronic Applanation Tonometers (e.g. Tono-Pen, Accupen)
- Accurate Tonometry alternative to the Goldmann Tonometer
- Non-contact Tonometers (air-puff)
- Least accurate Tonometry method, but no Topical Anesthetic needed
- Schiotz (older, manual method, rarely used in U.S.)
- Requires a skilled, practiced clinician to use accurately
- Scale <3.5 (5.5g plunger) recheck with 7.5g plunger
- Scale <6.0 (7.5g plunger) recheck with 10g plunger
- Scale <8.5 (10g plunger) recheck with 15g plunger
- Scale <11.0 (15g plunger)
IV. Interpretation
- Normal Intraocular Pressure
- Intraocular Pressure 8 to 21 mmHg
- Elevated Intraocular Pressure (Glaucoma)
- Intraocular Pressure > 21.5 mmHg
-
Decreased Intraocular Pressure (Ocular Hypotony)
- Intraocular Pressure <5 mmHg
V. Exam: Less accurate methods to estimate Intraocular Pressure
- Eye pressure applied through upper Eyelid
- Firmer eye suggests a higher Intraocular Pressure
- Anterior Chamber Depth
- Penlight illumination of anterior chamber
- Normal
- Illumination from lateral side lights entire iris
- Abnormal (increased pressure)
- Iris is bowed forward and nasal side is in shadow
- Nasal iris is not illuminated
VI. References
- Trobe (2012) Physician's Guide to Eye Care, AAO, p. 28