Effects of Corneal Thickness, Corneal Curvature, and Intraocular Pressure Level on Goldmann Applanation Tonometry and Dynamic Contour Tonometry
Presented at: Association for Research in Vision and Ophthalmology Annual Meeting, May 5, 2005, Fort Lauderdale, Florida.
Received 6 February 2006; accepted 12 June 2006. published online 27 October 2006.
Purpose
To compare the measurements of intraocular pressure (IOP) with Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) and the effects of central corneal thickness (CCT), corneal curvature, and level of IOP on these methods.
Design
Cross-sectional population-based study.
Participants
From the Los Angeles Latino Eye Study, 2157 participants of primarily Mexican ancestry.
Methods
Average GAT measurements were compared to DCT, and both were examined with respect to CCT (≤500, 501–550, 551–600, >600 microns), corneal curvature (<42, 42–46, >46 diopters), and level of IOP (0–10, 11–20, >20 mmHg).
Main Outcome Measures
Mean GAT and DCT IOP levels were compared for the entire population, and then trends for the CCT, curvature, and IOP groupings were analyzed. The magnitude of the difference of GAT minus DCT was compared for these different strata, with special attention to a difference of ± 3 mmHg or greater, which was defined as clinically significant.
Results
Mean IOP for the entire population by GAT was significantly lower (14.4±3.2 mmHg) compared with DCT (16.0±3.6; P<0.0001). Both GAT and DCT IOP levels were lowest for thin CCT and increased stepwise with increasing CCT, but this difference was more pronounced with GAT than DCT (P<0.0001 and P = 0.0012, respectively). The difference between GAT and DCT was largest for thin CCT and decreased for thicker CCT (P<0.0001). After adjusting for CCT, the corneal curvature affected IOP measured by DCT (P = 0.02) but not GAT (P = 0.3) such that mean DCT IOP increased with increasing corneal curvature. After adjusting for the CCT effect on IOP and stratifying by DCT IOP groups, the greatest difference between GAT and DCT was seen in the lowest IOP group (3.55±3.1), became negative in the intermediate group (−1.86±2.60), and was most negative in the highest IOP group (−3.88±3.3; P<0.0001).
Conclusions
Intraocular pressure measured by GAT was consistently lower when compared with DCT, and this difference was greatest with thinner CCT. Dynamic contour tonometry was also less affected by variations in CCT. Corneal curvature affected IOP measurements with DCT but not GAT, but this effect was less than the CCT effect on GAT. Goldmann applanation tonometry tended to underestimate IOP at higher levels and overestimate it at lower IOP levels when compared to DCT.
1Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California.
2Department of Biostatistics, Keck School of Medicine, University of Southern California, Los Angeles, California.
Correspondence to Rohit Varma, MD, MPH, Doheny Eye Institute, Suite 4900, 1450 San Pablo Street, Los Angeles, CA 90033.
Manuscript no. 2006-165.
Supported by the National Eye Institute and National Center on Minority Health and Health Disparities, Bethesda, Maryland (grant nos.: EY11753, EY03040).
The authors have no commercial or proprietary interest in the products or companies mentioned in the article.
ABSTRACT