Clinical comparison of contour and applanation tonometry and their relationship to pachymetry.
OBJECTIVE
To compare intraocular pressure readings of recently introduced dynamic contour tonometry (DCT) with pneumatonometry (PTG) and Goldmann applanation tonometry (GAT) and to correlate central corneal thickness (CCT) with these readings.


METHODS
Prospective, cross-sectional observation and instrument validation study. We included 258 independent eyes with normal anterior segment examinations results, irrespective of glaucoma diagnosis or glaucoma suspect. After pachymetry, DCT, PTG, and GAT were performed in a randomized order. Intraocular pressures as measured by DCT, PTG, and GAT were compared with each other and with CCT.


RESULTS
Eyes with thinner CCTs tended to yield lower intraocular pressure measurements by GAT. A significant correlation (Pearson product moment correlation, P<.001) between CCT and GAT was found with a regression of 0.25 mm Hg per 10 microm (R2 = 0.060). Variation of CCT had no significant effect on intraocular pressure measurements by PTG (P = .10; R2 = 0.01) and DCT (P = .80; R2<0.01). A piecewise regression model showed that GAT readings are not linearly correlated with CCT. Comparison of the slopes below and above 535 microm showed the highest significance (P<.001).


CONCLUSIONS
Goldmann applanation tonometry readings are potentially influenced by CCT, whereas PTG and DCT seem to be less dependent on CCT. Correlation between CCT and GAT is not linear. A simple correction formula suggesting a linear relationship might not be correct.
Kniestedt
Christoph
C
Department of Ophthalmology, University of California-San Francisco, USA. research@kniestedt.ch
Lin
Shan
S
Choe
Joyce
J
Bostrom
Alan
A
Nee
Michelle
M
Stamper
Robert L
RL
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000886:Anthropometry; D001699:Biometry; D003315:Cornea / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D003430:Cross-Sectional Studies; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000175:diagnosis*; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000175:diagnosis; D011446:Prospective Studies; D014065:Tonometry, Ocular / Q000379:methods*; D014463:Ultrasonography