Scanning-slit and specular microscopic pachymetry in comparison with ultrasonic determination of corneal thickness

Purpose. To determine the central corneal thickness values in healthy eyes with the recently developed Orbscan scanning-slit system, contact and nonco ntact specular microscopic pachymetry and compare the results to convention al ultrasonic pachymetry. Methods. In the following sequence, Orbscan, Topc on SP-2000P noncontact specular microscope, AL-1000 ultrasound, and Tomey c ontact specular microscope were used to record thickness values. Thirty-fou r healthy right corneas of 34 healthy subjects were investigated. Results. Orbscan pachymetry correlated significantly with ultrasound (r = 0.64, p < 0.001), contact (r = 0.45, p < 0.001), and noncontact specular microscopy ( r = 0.72, p < 0.001). Likewise, the Topcon SP-2000P noncontact specular mic roscopy pachymetry disclosed similar statistical results compared with ultr asound (r = 0.88, p < 0.001), and contact specular microscopy pachymetry (r = 0.76, p < 0.001). The mean central corneal thickness results were signif icantly higher (p less than or equal to 0.01) than ultrasonic values (580 /- 43 mum) using the contact specular microscope (640 +/- 43 mum) or Orbsca n system (602 +/- 59 mum) but were significantly, lower (p < 0.001) using t he noncontact specular microscope (547 +/- 49 mum). Conclusions. The result s indicate that the devices tested cannot be simply used interchangeably. F or long-term patient follow-up, one specific instrument is recommended. Rec ently developed pachymetry machines are especially helpful when additional corneal data such as thickness profile, elevation maps, anterior chamber de pth, and endothelial morphology are required.