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J.A. Evangelista, J.H. Oakman, D.L. Johnson, J.P. Tao, R. Trespalacios, A.D. Hitch; Central Corneal Thickness Changes After Goldmann Applanation Tonometry and Gonioscopy . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4855.
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Purpose: The role of pachymetry in the initial screening of glaucoma has been increasingly emphasized. Central corneal thickness (CCT) has been shown to not only affect applanation tonometry measurments but to be an independent risk factor for glaucomatous damage. If applanation by tonometry or gonioscopy compresses the cornea and changes CCT, the timing of when during the exam pachymetry is performed would be crucial to obtaining a corrected intraocular pressure and a proper risk stratification of glaucomatous damage. With newer ultrasonic pachymeters, there is good precision with a low standard deviation allowing for detection of even small changes in corneal thickness that may influence clinical management. Methods: One investigator (JAE) prospectively analyzed 24 patients randomizing one eye to undergo Goldmann applanation tonometry (Haag–Streit, Switzerland) and the other to gonioscopy by a Sussman four mirror gonioscopy lens (Ocular Instrument Inc, Bellevue, WA). After instillation of anesthetic drops, CCT was measured at baseline, 30 to 45 seconds after tonometry or gonioscopy, and 3 to 5 minutes after tonometry or gonioscopy. CCT measurements were taken with an ultrasonic pachymeter, DGH 55 Pachmate (DGH Technology Inc, Exton, PA), utilizing 25 consecutively automated measurements to obtain an average thickness. Mixed linear modeling with random eye effects and repeated time effects (SAS statistical analysis software, Cary, NC) was used to evaluate the relationship between the two groups. Results: Mean CCT (and mean standard deviation) at baseline, after 30–45 seconds, and after 3–5 minutes for the tonometry group was 540.21 (2.93), 540.25 (2.50), 539.54 (2.50), respectively; the gonioscopy group was 539.0 (3.12), 539.25 (3.14), 537.79 (2.73), respectively. No statistically significant difference in CCT was found over time for the two corneal applanation modalities or at any time point between the two applanation modalities. Conclusions: In this series of central corneal thickness measurements we did not find a significant change from before and after Goldmann applanation tonometry or gonioscopy by a Sussman gonioscopy lens. Central corneal thickness is a powerful predictor for the development of glaucomatous damage, and it is recommended that pachymetry be performed on all glaucoma suspect patients even those who have already undergone same day applanation tonometry and gonioscopy.
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