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Novel collagen imaging using ultra-high resolution polarisation sensitive optical coherence tomography in healthy, suspect and keratoconus corneas
First Author: D. Trivedi INDIA
Co Author(s): R. Shetty A. Roy R. Patil P. Khamar
To assess the distribution of collagen in healthy and keratoconus (KC) corneas, and correlate with early disease-related changes in the distribution of collagen in suspicious corneas, with the help of a custom built ultra-high-resolution polarisation sensitive OCT (PS-OCT).
Narayana Nethralaya, Bangalore
50 healthy corneas, 50 KC corneas and 35 suspicious corneas were imaged prospectively using ultra-high resolution PSOCT. Suspicious corneas were diagnosed clinically (slit lamp, corneal tomography and corneal biomechanics) by an experienced ophthalmologist. PSOCT studies the birefringence of collagen fibres to assess the distribution of collagen in corneal stroma which is often subnormal in ectatic corneal disorders like keratoconus. It generated 2 measures of collagen fibre distribution - phase retardation (PR) and axis orientation (AO), which were evaluated at each pixel of an OCT B-scan. Histograms of PR and AO were then created and analysed.
The PR and AO histograms of the healthy corneas matched exactly with the in-situ distribution of human donor corneas measured ex-vivo in earlier studies. In KC corneas, there was a marked reduction in the number of pixels with PR <25 degrees, with a concomitant increase in the number of pixels with AO <0 degrees (p<0.001). Surprisingly, the histograms of some suspect corneas matched those of the healthy corneas (n=10, p>0.05), while the remaining (n=25, p<0.01) had a unique distribution that was much different from those of KC corneas.
Novel PSOCT imaging clearly identified the differences in collagen distribution between healthy and KC corneas. Some of the asymmetric fellow corneas revealed a unique distribution of collagen, indicating early changes, before their topographic manifestations in these eyes. PS-OCT by imaging the collagen can help diagnose KC even in corneas with normal / suspicious topography and can serve as an excellent screening modality for early diagnosis of KC, and in refractive surgery screening to prevent post LASIK ectasia.
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