Influence of corneal structure, corneal responsiveness, and other ocular parameters on tonometric measurement of intraocular pressure.
OBJECTIVE
To estimate the relationships between ocular parameters and tonometrically measured intraocular pressure (IOP), to determine the influence of ocular parameters on different instrument measurements of IOP, and to evaluate the association of ocular parameters with a parameter called hysteresis.


METHODS
Patients presenting at a glaucoma clinic were recruited for this study. Subjects underwent IOP measurement with the Goldmann applanation tonometer (GAT), the TonoPen, and the Reichert Ocular Response Analyzer (ORA), and also measurements of central corneal thickness (CCT), axial length, corneal curvature, corneal astigmatism, central visual acuity, and refractive error. Chart information was reviewed to determine glaucoma treatment history. The ORA instrument provided a measurement called corneal hysteresis. The association between measured IOP and the other ocular characteristics was estimated using generalized estimating equations.


RESULTS
Among 230 patients, IOP measurements from the TonoPen read lowest, and ORA read highest, and GAT measurements were closest to the mean IOP of the 3 instruments. In a multiple regression model adjusting for age, sex, race, and other ocular characteristics, a 10 microm increase in CCT was associated with an increase of 0.79 mm Hg measured IOP in untreated eyes (P<0.0001). Of the 3 tonometers, GAT was the least affected by CCT (0.66 mm Hg/10 mum, P<0.0001). Hysteresis was significantly correlated with CCT with a modest correlation coefficient (r=0.20, P<0.0007).


CONCLUSIONS
Among parameters related to measured IOP, features in addition to CCT, such as hysteresis and corneal curvature, may also be important. Tonometric instruments seem to be affected differently by various physiologic characteristics.
Broman
Aimee Teo
AT
Dana Center for Preventive Ophthalmology, The Johns Hopkins School of Medicine, Baltimore, MD, USA. aibroman@jhmi.edu
Congdon
Nathan G
NG
Bandeen-Roche
Karen
K
Quigley
Harry A
HA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001699:Biometry; D003315:Cornea / Q000033:anatomy & histology* / Q000502:physiology*; D005123:Eye / Q000033:anatomy & histology; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000503:physiopathology; D012030:Refractive Errors / Q000503:physiopathology; D014065:Tonometry, Ocular