Improving interobserver variation in corneal sublayer pachymetry using ConfoScan4 with Z ring

Objectives: To observe and improve the interobserver variation of corneal sublayer pachymetry using ConfoScan4 (CS4) z ring. Methods: Right corneas of 34 normal subjects were scanned using CS4 (z ring) (Nidek Technologies, Padova, Italy). Corneal sublayer pachymetry was performed by two masked observers based on the written frame selection criteria from literature. The full stromal thickness (FST), epithelial and Bowman layer thickness (Epi+BT), endothelial thickness (EndoT), and total corneal thickness (CT) were obtained. Upon completion of the measurements (measurement 1), the frame selection criteria were reviewed between the observers by going through some corneal frames together. Eight subjects were excluded and corneal sublayer pachymetry was re-evaluated by the two observers using the revised criteria (measurement 2). Results: Corneal thickness showed significant interobserver difference in measurement 1 (n=34), but no significant difference in measurement 2 (n=26). Endothelial thickness remained significant difference between observers throughout the study. Interobserver difference significantly reduced using the revised criteria in CT (1.93 ± 3.23 μm to 0.28 ± 1.75 μm) and EndoT (4.01 ± 4.82 μm to 0.86 ± 1.81μm). There was no significant difference between observers in Epi+BT and FST for the two measurements. Interobserver variation and the 95% confidence limits between observers for CT and corneal sublayers were reduced at least by half in measurement 2. Conclusions: The interobserver variation in corneal sublayer pachymetry could be improved by having the observers going through some corneal frames together rather than just following the written criteria. The use of CS4 (z ring) to measure CT, FST, and Epi+BT is suitable for monitoring corneal changes clinically.