Optical Coherence Tomography Combined With Videokeratography to Differentiate Mild Keratoconus Subtypes

PURPOSE: To develop parameters using a combination of optical coherence tomography (OCT) and videokeratography to detect early keratoconus. METHODS: Videokeratography, wavefront analysis, and measured OCT indices were performed on 180 normal eyes, 46 eyes with moderate keratoconus, 54 eyes with early keratoconus, 7 eyes with forme fruste keratoconus, and 16 eyes with keratoconus "suspect" to determine the most sensitive parameters for separating these groups. RESULTS: A combination of videokeratography and OCT indices (inferior-superior [I-S] value and minimum pachymetry) was statistically the most significant in separating the keratoconus groups from normal eyes (P < .001). Using a newly derived index, the minimum pachymetry divided by the I-S value (pachymetry/asymmetry [PA]/I-S index) with a cut-off of 100, 100% of early and forme fruste keratoconus could be identified as being abnormal with 7 normals misclassified (misclassification rate 2.7%). By adding keratoconus "suspect" to the analysis and an I-S value of 1.2 as a cut-off point, 5 "suspects" were classified as normal and 11 normals as abnormal (misclassification rate 7.8%). The PA/I-S index, with a cut-off point of 100, reduced this misclassification rate to 4.4%. CONCLUSIONS: These results suggest that OCT combined with videokeratography may be more useful for differentiating mild forms of keratoconus than videokeratography alone.