Purpose: To evaluate the central corneal thickness values in normal and postkeratoplasty corneas with the new Topcon SP-2000P noncontact specular microscopic, contact specular microscopic, and the "common standard" ultrasonic pachymetry.
Methods: Central corneal thickness was determined in 119 eyes of 81 patients (73 normal eyes of 44 patients and 46 eyes after penetrating keratoplasty) first with a noncontact specular microscopic (Topcon SP-2000P; Topcon Corporation, Tokyo, Japan), then an ultrasonic (AL-1000; Tomey, Erlangen, Germany), and finally with a contact specular microscopic (EM-1000; Tomey, Erlangen, Germany) pachymetry two times each by the same investigator.
Results: Reliability of the central corneal measurements was equally high both in normal and in postkeratoplasty corneas with all of the instruments (Cronbach alpha = 0.99). Noncontact specular microscopic corneal thickness determination correlated significantly both with ultrasonic (r =.86, P <.0001) 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 microm) was 28 +/- 4 microm lower (P <.0001) compared with the ultrasonic data (570 +/- 42 microm), which was 68 +/- 1 microm lower (P <.0001) compared with Tomey thickness (638 +/- 43 microm).
Conclusions: Central corneal thickness measurements with noncontact specular microscopic, contact specular microscopic, and ultrasonic pachymetry demonstrate that each of the instruments is reliable but cannot be simply used interchangeably.