The effect of corneal edema on dynamic contour and goldmann tonometry.
OBJECTIVE
To determine the effect of contact lens-induced corneal edema on measurements of intraocular pressure (IOP) using the Pascal dynamic contour tonometer (DCT), compared with the Goldmann tonometer.


METHODS
Thirty young healthy subjects (23.0 +/- 3.0 years) were recruited from the student population at the University of New South Wales. Thick hydroxyethyl methacrylate contact lenses were worn monocularly for 2 hours under closed-eye conditions to induce corneal edema via hypoxia. IOP (Goldmann and Pascal DCT), ocular pulse amplitude (OPA), and central corneal thickness (CCT) were measured in both eyes before and after lens wear. Paired t-tests, Pearson correlation, and Bland-Altman plots were used to identify changes in, and relationships between, these parameters resulting from corneal edema.


RESULTS
Lens wear resulted in statistically significant changes in CCT (+48.3 +/- 14.4 microm, p < 0.001), Goldmann IOP (+1.5 +/- 2.8 mm Hg, p = 0.007), and Pascal DCT IOP (-0.7 +/- 1.1 mm Hg, p = 0.001) but not OPA (0.0 +/- 0.3 mm Hg, p = 0.721, two-tailed paired t-test). The Pascal DCT provided IOP readings that were 1.3 +/- 2.0 mm Hg higher than the Goldmann IOP readings when hydration was normal, but the Goldmann tonometer provided readings that were 0.8 +/- 2.5 mm Hg higher than the Pascal DCT readings when the cornea was edematous. The variation between the two instruments was weakly correlated to the change in CCT (r = -0.261, p = 0.044).


CONCLUSIONS
Contact lens-induced corneal edema caused a small underestimation error in IOP measurements by the Pascal DCT, and an overestimation error in Goldmann tonometry measurements. The OPA measurement provided by the Pascal DCT is insensitive to corneal edema-induced changes in corneal properties.
Hamilton
Kirsten E
KE
School of Optometry & Vision Sciences, Cardiff University, Cathays, Cardiff, Wales, United Kingdom. hamiltonke1@cardiff.ac.uk
Pye
David C
DC
Kao
Lawrence
L
Pham
Nhung
N
Tran
An-Quyen Nguyen
AQ
D000293:Adolescent; D000328:Adult; D003261:Contact Lenses / Q000009:adverse effects; D003315:Cornea / Q000033:anatomy & histology / Q000503:physiopathology; D015715:Corneal Edema / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure; D008365:Manometry / Q000379:methods*; D011674:Pulse; D011932:Reading; D012171:Retinal Vessels / Q000503:physiopathology; D014792:Visual Acuity