Forward light scatter and contrast sensitivity in keratoconic patients

The aim of this study was to obtain intraocular forward light scatter (FLS) data in keratoconus patients and to explore possible relationships with contrast sensitivity.

Intraocular straylight was assessed in the right eye of 10 visually-normal subjects (31±5 years) and 5 keratoconus patients (34±9 years) using the van den Berg straylight meter. Contrast sensitivity was also measured in both groups, with and without a glare source provided by the Brightness Acuity Tester (BAT), using a Pelli-Robson chart. Inclusion criteria for the keratoconic patients were chosen to avoid natural causes of increased scatter and to limit the influence of factors that could affect the straylight measurements.

Intraocular light scatter was significantly greater in the keratoconic patients than in normal subjects for each of the three eccentricities tested (Mann-Whitney U test (2-tailed): Z≤-2.2, p≤0.027). Baseline Pelli-Robson contrast sensitivity was also found to be lower in the keratoconus group than in the normal subjects (Mann-Whitney U test: Z=-2.2, p=0.023). Under glare conditions contrast loss was significantly greater in the keratoconic patients than in the normal subjects (Mann-Whitney U test: Z=-2.5, p=0.013). High levels of negative correlation were found between the magnitudes of intraocular straylight and baseline contrast sensitivity in the keratoconus group (Spearman's correlation coefficient (RS)≤-0.87, p≤0.027).

The high values of straylight measured in the keratoconic patients cannot be explained by age or scarring and could be related to the structural degradation of the cornea. Further investigation of intraocular scatter in keratoconus is warranted to improve our current understanding of the visual deficits associated with this pathology.