Early biomechanical keratoconus pattern measured with an ocular response analyzer: Curve analysis

PURPOSE: To estimate the ability of the Ocular Response Analyzer parameters to aid in the diagnosis of keratoconus in pre-laser in situ keratomileusis (LASIK) patients. SETTING: Department of Ophthalmology, Bordeaux 2 University, Bordeaux Cedex, France. DESIGN: Evaluation of diagnostic test. METHODS: This study compared eyes with mild stages of keratoconus (study group) with preoperative eyes that later had LASIK (control group). Corneas with a central thickness within 500 to 600 mu m were targeted. The biomechanical measurements were acquired, and 12 parameters were analyzed after extraction from the signal data. RESULTS: The study group comprised 103 eyes and the control group, 97 eyes. The mean corneal hysteresis (CH) was 9.2 mm Hg in study eyes and 10.1 mm Hg in control eyes and the mean corneal resistance factor (CRF), 8.9 mm Hg and 10.6 mm Hg, respectively. For a threshold of 9.6, CH had a sensitivity of 66% with a specificity of 67%. For a threshold of 9.7, the CRF had a sensitivity of 72% and a specificity of 77%. For 6 biomechanical parameters, the probability that a patient would present with keratoconus was 3 in 1000 if 1 parameter was over the chosen threshold. CONCLUSIONS: If 1 of 6 parameters were over a chosen threshold, the probability that a patient would present with keratoconus would be almost 3 in 1000 instead of 9 in 1000 in a LASIK surgery cohort. Despite low sensitivity and specificity, some parameters provided by the corneal analyzer offered high negative likelihood ratios and deserve more study with bigger samples.