The relationship of Central Corneal Thickness (CCT) to Thinnest Central Cornea (TCC) in healthy adults.

Purpose: The aim of the study was to precisely quantify the relationship between the central corneal points, namely the pupillary centre and the thinnest point in the central cornea, in terms of their thickness and location in healthy adults.

Methods: 120 eyes of 60 healthy adult volunteers underwent pachymetry with a Scheimpflug imaging system (Pentacam). The thickness at the pupillary centre (Central Corneal Thickness, CCT) and the thickness at the Thinnest Central Corneal (TCC) point were measured. One eye of each patient was used to analyse the mean difference between CCT and TCC. Unpaired t-test (one tailed) was used to test significance and 95% confidence limits were used. The precise location of the TCC in relation to the corneal apex was measured using vector algebraic and trigonometric calculations.

Results: The mean CCT was 520+/-33microm and the TCC was 515+/-36microm. The difference between CCT and TCC was found to be 5.57microm (0-15.9microm, 95% CI; P=0.1909). The TCC location was inferotemporal to the corneal apex in 58/60 (96.7%) of the right eyes and in 49/60 (81.7%) of the left eyes. The average vector location of TCC of both eyes was inferotemporal. This coordinate was found to lie 0.62mm (right eye) and 0.79mm (left eye) from the corneal apex subtending and angle of 45.5 degrees (right eye) and -10.9 degrees (left eye) from the horizontal.

Conclusion: The study has identified the parameters of TCC and its relationship to CCT in terms of the location and thickness. For clinical usage, they can be interchangeable as there is no significant difference between the two. The consistency in the (inferotemporal) location of the TCC merits further research in this regard to the development of corneal ectasia.