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J.H. Wang, I. Cox; The thickness profile of corneal flaps created with a microkeratome using real–time optical coherence tomography . Invest. Ophthalmol. Vis. Sci. 2004;45(13):191.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: All current methods of measuring the thickness profile of corneal flaps in pig–eye models created with a microkeratome involve contacting the tissue itself, which potentially could introduce an error in the measurement. The aim of this study was to demonstrate the feasibility of a novel, non–contact method using real–time optical coherent tomography (OCT) at 1310nm with a telecentric design to measure the entire corneal flap thickness in vitro. Methods:Corneal flaps created with a microkeratome (Bausch & Lomb investigative version, flap diameter 8.5mm and thickness 200µm) from 11 freshly enucleated pig eyes were placed on a glass plate and scanned with the real–time OCT to measure the physical thickness of the flap independent of the refractive index of the tissue. The entire flap was scanned at the meridian where the corneal hinge was located. The other scan meridian was perpendicular to the hinge meridian (where there was no corneal hinge). Each flap image was averaged from 9 raw images. Corneal thickness at locations from edge to edge (or edge to hinge) at 0.5mm intervals was obtained using custom software by analysis of 11 longitudinal scans at each location. Results: OCT thickness measurements across the entire flap at both studied meridians were significantly different (ANOVA: p<0.0001) with a significantly thinner edge at 0.5mm (about 150µm, post–hoc test: p<0.0005, compared to any other locations) from any edges except for the hinge. The greatest flap thickness was 226.8µm located at 3mm from the edge on the hinge meridian, and 229.4µm located at 4.5mm from the edge at the non–hinge meridian. The mean thickness (from 1mm to 7.5mm locations) of the entire flap was 219.7 ±10.1 (Mean ± SD: µm) for non–hinge meridian and 215.8 ± 6.5 (two–tailed, paired t–test: p=0.06) for the hinge meridian. Conclusions: This novel method using OCT to measure the entire flap thickness appears to be useful to study the corneal flap and verify microkeratome performance. (This study has been supported by a research grant from Bausch & Lomb)
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