Effects of central corneal thickness and corneal curvature on the intraocular pressure measurement by Goldmann applanation tonometer and ocular blood flow pneumatonometer.
OBJECTIVE
To assess the effects of central corneal thickness (CCT) and corneal curvature (CC) on the measurements of intraocular pressure (IOP) using Goldmann applanation tonometer (GAT) and the ocular blood flow pneumatonometer (OBFT).


METHODS
104 patients were recruited from a glaucoma clinic. The CCT was measured using ultrasound pachymetry and the mean radius of CC using a keratometer. The IOP of each eye was measured using both GAT and the OBFT in a random order. Right eyes only were analysed for statistical purposes.


RESULTS
The mean (+/-SD) IOP by GAT and OBFT was 18.2 mmHg (+/-4.4) and 18.2 mmHg (+/-4.0), respectively, with no statistically significant difference. IOP measurement with both instruments varied with CCT and CC. GAT showed an IOP increase of 0.40 mmHg per 10 microm increase of CCT and OBFT showed an increase of 0.38 mmHg in IOP per 10 microm increase of CCT. Multiple regression analysis showed that the effect of CCT was statistically significant (P<0.001) on IOP recorded by both the GAT and OBFT but CC did not have a statistically significant effect on IOP recordings performed by either technique.


CONCLUSIONS
IOP measurements by GAT and OBFT are positively correlated with CCT with both tonometers being similarly affected. There was no significant correlation between CC and IOP measured by either tonometer.
Saleh
Tarek A
TA
Taunton and Somerset Hospital, Musgrove Park, Taunton, UK. tareksaleh@doctors.org.uk
Adams
Morag
M
McDermott
Bill
B
Claridge
Kate G
KG
Ewings
Paul
P
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001837:Body Weights and Measures; D003315:Cornea / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D005902:Glaucoma, Open-Angle / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000150:complications / Q000503:physiopathology; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000295:instrumentation / Q000379:methods*; D014463:Ultrasonography