NHMRC Glaucoma Guidelines - ANZGIG

NHMRC GUIDELINES FOR THE SCREENING, PROGNOSIS, DIAGNOSIS, MANAGEMENT AND PREVENTION OF GLAUCOMA
Chapter 7 – Diagnosis of glaucoma
Point of note
Peaks and troughs in intraocular pressure occur at different times in different people. The true
correction for central corneal thickness is not known, and any value is at best an approximation.
Non-contact tonometry
Pneumatonometry: Air-puff tonometry uses a rapid air pulse to applanate the cornea. Corneal
applanation is detected via an electro-optical system. IOP is estimated by detecting the force of the
air jet at the instance of applanation. Non-contact tonometry is especially useful for very young
children, patients unable to reach a slit lamp due to disability, patients who are uncooperative
during applanation tonometry, or patients with corneal disease in whom contact tonometer cannot
be accurately performed. In addition, it should be considered for patients who simply cannot
tolerate physical contact on the cornea.
Alternative forms of tonometry
Electronic indentation tonometry
Tono-Pen (Reichert, Inc) is a form of electronic indentation tonometry. It is a portable electronic,
digital pen-like instrument that determines IOP by making contact with the cornea, after topical
anaesthetic eye drops have been applied.
Perkins tonometry
This is a specific type of portable applanation tonometer to measure IOP in children, patients
unable to cooperate for slit lamp exam, and supine anesthetised patients.
The relative merits of each form of tonometry are outlined in Table 7.4. This information was
extracted from Burr et al (2007).
Table 7.4: The relative merits of each form of tonometry
IOP
measurement
Glaucoma
stage
Sensitivity
(95%CI)
Specificity
(95%CI)
DOR
(95%CI)
Goldmann Applanation
Tonometry
Non-contact
(air-puff) tonometry
Pooled all stages 46 (22-71) 95 (89-97) 4.95 (4.48-48.95)
Pooled all stages 92 (62-100) 92 (90-94) 134.88 (17.15-1061.1)
The use of non-applanation tonometry (i.e. dynamic contour forms) has recently been reported in
the literature. There is insufficient evidence to date of the true place of dynamic contour tonometry
or other tonometric methods compared to Goldmann Applanation Tonometry. Future updates of
this guideline will address this issue should research become available.
Point of note
To accommodate patient preference and to ensure secondary confirmation of findings, a variety of
methods for measuring intraocular pressure are required.
National Health and Medical Research Council 79