Effect of corneal thickness on intraocular pressure measurements with the pneumotonometer, Goldmann applanation tonometer, and Tono-Pen.
OBJECTIVE
To compare intraocular pressure (IOP) measurements of the Ocular Blood Flow (OBF) pneumotonometer, Goldmann applanation tonometer, and Tono-Pen in eyes with normal corneas of various thicknesses.


METHODS
IOP was measured with an OBF pneumotonometer, Tono-Pen and Goldmann applanation tonometer in random order in 181 eyes with normal corneas. Central corneal thickness (CCT) was measured using an ultrasonic pachymeter after all IOP determinations had been made. Right and left eyes were analyzed separately for statistical purposes.


RESULTS
With all instruments, IOP varied with CCT, even though the variation in IOP was large. Readings with the OBF pneumotonometer showed a mean increase in IOP with increasing CCT of 0.28 mm Hg/10 microm, an increase of 0.23 mm Hg/10 microm with the Goldmann tonometer, and of 0.10 mm Hg/10 microm with the Tono-Pen. The OBF pneumotonometer consistently recorded comparatively higher IOPs than the other two instruments.


CONCLUSIONS
The Tono-Pen is least affected by CCT when used to measure IOP in eyes with normal corneas. The OBF pneumotonometer appears to be more affected by variation in CCT than the Goldmann tonometer. This is contrary to expectations, based on the mechanism of measurement of IOP of the OBF pneumotonometer.
Bhan
Archana
A
Division of Ophthalmology and Visual Sciences, Queens Medical Centre, Derby Road, Nottingham NG7 2UH, United Kingdom.
Browning
Andrew C
AC
Shah
Sunil
S
Hamilton
Robin
R
Dave
Dinesh
D
Dua
Harminder S
HS
D003315:Cornea / Q000033:anatomy & histology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000379:methods* / Q000592:standards