Corneal thickness measurements with contact and noncontact specular microscopic and ultrasonic pachymetry

PURPOSE: To evaluate the central corneal thickness values in normal and pos tkeratoplasty corneas with the new Topcon SP-2000P noncontact specular micr oscopic, contact specular microscopic, and the "common standard" ultrasonic pachymetry. METHODS: Central corneal thickness was determined in 119 eyes of 81 patient s (73 normal eyes of 44 patients and 46 eyes after penetrating keratoplasty ) first with a noncontact specular microscopic (Topcon SP-2000P; Topcon Cor poration, Tokyo, Japan), then an ultrasonic (AL-1000; Tomey, Erlangen, Germ any), and finally with a contact specular microscopic (EM-1000; Tomey, Erla ngen, Germany) pachymetry two times each by the same investigator. RESULTS: Reliability of the central corneal measurements was equally high b oth in normal and in postkeratoplasty corneas with all of the instruments ( Cronbach alpha = 0.99). Noncontact specular microscopic corneal thickness d etermination correlated significantly both with ultrasonic (r = .86, P < .0 001) and contact specular microscopic pachymetry (r = .62, P < .0001). The ultrasonic pachymetry correlated well with the Tomey pachymetry (r = .69, P < .0001). The Topcon normal mean central corneal thickness value (542 +/- 46 mum) was 28 +/- 4 mum lower (P < .0001) compared with the ultrasonic dat a (570 +/- 42 mum), which was 68 +/- 1 mum lower (P < .0001) compared with Tomey thickness (638 +/- 43 mum). CONCLUSIONS: Central corneal thickness me asurements with noncontact specular microscopic, contact specular microscop ic, and ultrasonic pachymetry demonstrate that each of the instruments is r eliable but cannot be simply used interchangeably. (C) 2001 by Elsevier Sci ence Inc. All rights reserved.