Forward and backward light scatter measurements in the assessment of corneal oedema

Abstract

As the cornea swells it loses its transparency, thereby increasing both forward and backward light scatter. The purpose of this study was to investigate the changes in corneal transparency by means of scatter assessment. Both forward and backward light scatter measurements were obtained from 18 normal corneas, before and after the induction of corneal oedema with sealed scleral lenses. Forward light scatter was measured at 3.5, 10 and 28 degrees, using a portable straylight meter as developed by van den Berg. Backward light scatter measurements were obtained by computerised linear scanning densitometry of Scheimpflug images using the Oxford Modular Cataract Image Analysis System. After the scleral lenses were worn, forward light scatter values increased significantly at all the three angles (3.5°: F1,17 = 65.69, P < 0.001; 10° : F1,17 = 37.30, P < 0.001; 28°: F1,17 = 26.66, P < 0.001). Backward light scatter also increased significantly with the presence of corneal oedema (F1,17 = 3 4.80, P < 0.001). A significant correlation was found between the differences on forward light scatter recorded at the different angles. However, no significant correlation was found between the increase in forward and backward scatter recorded by the two techniques. We conclude that both forward and backward light scatter can be good indicators of corneal transparency.