| Purpose: Central corneal thickness ( CCT ) is routinely measured in ophthalmic practice, sometimes with more than one instrument. One must establish reliability and repeatability as well as comparison between the various instruments. We compared CCT obtained with the Orbscan II, Micropach 200+ and the HRT-II scanning laser confocal microscope (HRT-SLCM). Setting/ Venue: All readings were performed in an anterior segment ophthalmology private practice. Material and Methods: 100 eyes of 50 consecutive patients underwent assessment of CCT. After instillation of Tetracaine 1% eyedrops CCT readings were obtained from the Orbscan followed by three readings from the Micropach 200 that were averaged. The probe was kept perpendicular to the surface of the cornea. Then, CCT readings were obtained using the HRT-II corneal module. One eye was used for fixation. The cornea being examined was kept perpendicular to the confocal lens. Once contact was obtained between the lens and the anterior surface of the cornea, the lens was advanced till the endothelium was reached. The CCT was noted. Results: Mean corneal thickness measured by the HRT was significantly more (P<.05) than the mean value obtained with the ultrasound pachymeter. Similarly, mean values obtained with the 3 instruments by the 2 investigators were significantly different with the HRT value more than the ultrasound and Orbscan values in both cases. However, the measurements obtained with the Orbscan by the 2 investigators were more consistent (no significant difference) than those obtained with the ultrasound unit. Conclusions: The HRT-SLCM provides CCT measurements that show decreased consistency from one operator to another. Antero-posterior (z axis) movement and inter-user bias in x/y axis placement in corneal contact might be responsible. HRT II CCT readings might not be ideal for comparisons of readings by different operators over time. Financial Disclosure: NO. |
