Effect of epithelial and stromal edema on the light scattering properties of the cornea.

Transparency of the cornea is dependent on normal metabolism. Any disturbance in function, e.g., corneal edema, results in increased light scattering, reducing contrast sensitivity, and increasing glare susceptibility. A psychophysical method was developed to quantify this visual disability and to separate sources of light scatter within the cornea using three conditions: a no glare condition, a 30 degree angular radius glare condition, and a 3.5 degrees angular radius glare condition. Corneal edema was induced (N = 7) and contrast threshold measurements were recorded for 15 min during edema recovery using a clinically available technique. Retinal contrast attenuation was expressed in terms of light scattering factors (LSFs). Results show that the technique devised separates attenuation of retinal image contrast caused by epithelial and stromal edema and provides quantifiable values for normal light scatter and for that due to epithelial and stromal elements.