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Jay W McLaren, Katrina M Kane, Katrin Wacker, Sanjay V Patel; Measurement of Corneal Backscatter by Scheimpflug and Confocal Microscopy.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1616.
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© ARVO (1962-2015); The Authors (2016-present)
The Scheimpflug camera can provide fast, non-contact estimates of corneal haze (backscatter) from image brightness, but it is unknown if these estimates are equivalent to measurements of corneal haze from other instruments. In this study we compared backscatter estimated from a Scheimpflug camera with backscatter estimated from a clinical confocal microscope in a group of subjects with a wide range of corneal haze.
Forty eyes from 25 patients with Fuchs Endothelial Dystrophy (high haze) and 12 eyes from 6 normal participants (low haze) were examined by using a Scheimpflug camera (Pentacam, Oculus). The mean image brightness (backscatter) from the anterior 120 µm, mid-stroma, and posterior 60 µm of the cornea, across the central 2 mm were calculated by the native software. The same eyes were then scanned by using a clinical confocal microscope (ConfoScan 4, Nidek Technologies) and mean image brightness at similar anterior, mid-stromal, and posterior depths was calculated. Image brightness from each instrument was standardized to a fixed scatter source and expressed as “Scatter Units” (SU), the concentration of Amco Clear (GFS Chemicals) that gave the same image brightness as the corneal image. Generalized estimating equation models (paired tests and regression) were used to explore differences and correlation between the two instruments and to adjust for possible correlation between fellow eyes of the same subject.
Backscatter measured by the Scheimpflug camera in the anterior and mid-stroma were correlated with backscatter measured by the confocal microscope (p<0.001), although the mean slope of the regression lines was 0.45 (Figure). Mean backscatter from the anterior and mid-stroma were greater with the Scheimpflug camera than with the confocal microscope (p<0.001). Backscatter from the posterior cornea was lower when measured by the Scheimpflug camera (p<0.001).
The relationship between backscatter measured by these two instruments varies with depth in the cornea. Differences may be from the optical design of each instrument and the ratio of scattered to reflected light. These instruments should not be used interchangeably for measuring corneal haze.
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