Corneo-scleral limbus demarcation from 3D height data

- An accurate limbal demarcation methodology from 3D height data is proposed.
- Two techniques based on the same principle are presented and compared.
- Results are repeatable and accurate.
- Limbus does not necessarily coincide with corneo-sclera(iris) color transition.
- Limbus is not necessarily symmetric.

PurposeTo accurately and precisely demarcate the transition points in the anterior limbal surface from 3D anterior eye height data.MethodsData of anterior eye surface was acquired using a corneo-scleral profilometer. Two methods for automatic limbal radius estimation were proposed. One is based on the residual error between the original data and low order fit data while the other method takes a step further, calculating the cumulative root mean square (RMS) of the residual error. Data of a simulated example, collected from an artificial bi-sphere test surface and four real eyes is used to validate the methodology.ResultsBoth methods of limbal radius estimation were found to be equivalent in a low noise regime while the residual RMS method performs better in higher noise regimes. The relative error for the proposed methods was below 0.05% and below 1.1% for the simulated test surface and the artificial bi-sphere, respectively. For the four considered subjects, the variability of the methods was less than 10 μm. There was no statistically significant difference between methods nor between method and subject but there was statistically significant difference between the subjects (two-way ANOVA, p < 0.001). Asymmetry in limbal shape between nasal and temporal side was observed.ConclusionsDetermining the anterior limbus position in a non-invasive, automatic, accurate and precise manner is possible using 3D anterior eye height data. The topographical information of limbus does not necessarily coincide with the maximum rate of change in colour from the iris to sclera observable with en-face imaging.