Effects of corneal thickness, corneal curvature, and intraocular pressure level on Goldmann applanation tonometry and dynamic contour tonometry. 2007

Brian A Francis, and Amy Hsieh, and Mei-Ying Lai, and Vikas Chopra, and Fernando Pena, and Stanley Azen, and Rohit Varma, and
Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.

OBJECTIVE 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. METHODS Cross-sectional population-based study. METHODS 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 (< or =500, 501-550, 551-600, >600 microns), corneal curvature (<42, 42-46, >46 diopters), and level of IOP (0-10, 11-20, >20 mmHg). METHODS 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.

UI MeSH Term Description Entries
D007429 Intraocular Pressure The pressure of the fluids in the eye. Ocular Tension,Intraocular Pressures,Ocular Tensions,Pressure, Intraocular,Pressures, Intraocular,Tension, Ocular,Tensions, Ocular
D008297 Male Males
D008875 Middle Aged An adult aged 45 - 64 years. Middle Age
D001837 Body Weights and Measures Measurements of the height, weight, length, area, etc., of the human and animal body or its parts. Body Measures,Body Measure,Measure, Body,Measures, Body
D003315 Cornea The transparent anterior portion of the fibrous coat of the eye consisting of five layers: stratified squamous CORNEAL EPITHELIUM; BOWMAN MEMBRANE; CORNEAL STROMA; DESCEMET MEMBRANE; and mesenchymal CORNEAL ENDOTHELIUM. It serves as the first refracting medium of the eye. It is structurally continuous with the SCLERA, avascular, receiving its nourishment by permeation through spaces between the lamellae, and is innervated by the ophthalmic division of the TRIGEMINAL NERVE via the ciliary nerves and those of the surrounding conjunctiva which together form plexuses. (Cline et al., Dictionary of Visual Science, 4th ed) Corneas
D003430 Cross-Sectional Studies Studies in which the presence or absence of disease or other health-related variables are determined in each member of the study population or in a representative sample at one particular time. This contrasts with LONGITUDINAL STUDIES which are followed over a period of time. Disease Frequency Surveys,Prevalence Studies,Analysis, Cross-Sectional,Cross Sectional Analysis,Cross-Sectional Survey,Surveys, Disease Frequency,Analyses, Cross Sectional,Analyses, Cross-Sectional,Analysis, Cross Sectional,Cross Sectional Analyses,Cross Sectional Studies,Cross Sectional Survey,Cross-Sectional Analyses,Cross-Sectional Analysis,Cross-Sectional Study,Cross-Sectional Surveys,Disease Frequency Survey,Prevalence Study,Studies, Cross-Sectional,Studies, Prevalence,Study, Cross-Sectional,Study, Prevalence,Survey, Cross-Sectional,Survey, Disease Frequency,Surveys, Cross-Sectional
D005260 Female Females
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000328 Adult A person having attained full growth or maturity. Adults are of 19 through 44 years of age. For a person between 19 and 24 years of age, YOUNG ADULT is available. Adults
D000368 Aged A person 65 years of age or older. For a person older than 79 years, AGED, 80 AND OVER is available. Elderly

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