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Katie Marie Hallahan, Karolinne Rocha, Abhijit Sinha Roy, James Bradley Randleman, R Doyle Stulting, William J Dupps; Effects of corneal collagen crosslinking on Ocular Response Analyzer Waveform-derived variables in keratoconus and post-LASIK ectasia. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3722.
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To assess changes in Ocular Response Analyzer (ORA) waveforms after UVA/riboflavin corneal collagen crosslinking (CXL) using investigator-derived and manufacturer-supplied morphometric variables in keratoconus and post-LASIK ectasia patients.
Patients with progressive keratoconus (24 eyes of 21 patients) or post-refractive surgery ectasia (27 eyes of 23 patients) enrolled in a prospective, randomized trial of epithelium-off CXL were included. Replicate ORA measurements were obtained prior to and 3 months after CXL. Pre-treatment and post-treatment waveform variables were analyzed for differences by paired student’s t-tests.
Pre-CXL corneal hysteresis (CH) and corneal resistance factor (CRF) were similar between the keratoconus and ectasia groups (p>.05). In keratoconus eyes, CRF and waveform-derived variables were not significantly altered by CXL (p>.06), whereas CH was significantly lower after CXL. In ectasia eyes, neither CH nor CRF were significantly different after CXL. However, evidence of increased bending resistance after CXL from custom variables included significant increases in the force and time required to achieve applanation, an increase in the pressures at each applanation event, a decrease in the duration of corneal concavity, and an increase in the elapsed time to the first applanation peak (p<.05). In the ectasia group, only one ORA beta variable (w11) was significantly different after CXL.
CRF was insensitive to corneal biomechanical changes induced by collagen crosslinking. CH in keratoconus eyes was significantly lower after crosslinking, which reflects a decrease in viscous damping and is not incompatible with an increase in elastic strength. Certain investigator-derived variables were altered in a manner consistent with increased bending resistance after treatment.
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