ESTABLISHING GROUND TRUTH FOR KERATOCONUS PROGRESSION: DEFINING ADAPTIVE THRESHOLDS AND IMPROVING PRECISION IN CORNEAL OPTICAL COHERENCE TOMOGRAPHY

Keratoconus progression is defined with reference to precision limits in corneal tomography. We set out to perform a comprehensive analysis of measurement precision using a contemporary corneal tomography device (MS-39, CSO Italia, Florence, Italy) in a large sample of patients with keratoconus. 

Moorfields Eye Hospital, London, UK.

Single observer (repeatability) and multiple observer (reproducibility) precision were compared in a prospective series of 1,248 scans (n= 208 eyes). 95% repeatability coefficients (RC) for key corneal tomographic indices were then mapped at each unit interval through the measurement range in a retrospective analysis of 13,734 scans from 4,578 eyes to examine the effect of disease severity on precision. Finally, measurement repeatabiity for single measures was compared to measuremnt repeatability for the mean of of 3 consecutive measures.   

No significant differences were found between single and multiple observer precision (p>0.05 for all parameters). Measurement repeatablity deteriorated as keratoconus advanced for all indices examined. Combined measurement data (the mean of 3 scans) improved precision by an average of 43.9% versus single scans. 

Measurement precision in MS-39 corneal tomography is not significantly influenced by the operator where technicians are working with common scan acquisition protocol. Adaptive progression thresholds tailored to disease severity and device specific precision limits are necessary for the accurate detection of keratoconus progression. Averaging multiple scans improves precision, potentially allowing earlier detection of keratoconus disease progression.