QUANTIFYING STRAYLIGHT

A new compact instrument developed at the University of Murcia in Spain could be an important step forward in achieving the challenging task of optical measurement of straylight in the human eye. This in turn could improve the grading of cataracts in the clinical setting.

Speaking at the XXXIII Congress of the ESCRS in Barcelona, Spain, Harilaos Ginis PhD presented data from the first clinical evaluation of a prototype device that validated its performance and sensitivity for cataract detection and classification.

“Our instrument was developed for rapid measurement of intraocular scattering in a clinical setting. The testing is done without pupil dilation and provides a single parameter that quantifies the intensity of forward scattered light. Findings from our initial clinical evaluation demonstrate that the data it provides correlate well with psychophysically derived measurements of straylight and support its suitability for grading cataracts,” reported Dr Ginis, of the Research Institute of Optics and Nanophysics, University of Murcia.

The instrument, known as Sigma, is based on the optical integration method and utilises green (540nm) high brightness light emitting diodes as the light source. The light source is divided into two concentric zones - a disk corresponding to a visual angle of 3° and an annulus (3° to 8°) corresponding to the straylight measurement range.

AVOID BACKSCATTERING

“Various studies indicate that backscattering from the cornea and the lens is not strongly correlated to forward scattering that is visually relevant. By projecting the light source through the upper half of the pupil and with imaging done through the lower half, our instrument is designed to avoid backscattering and spurious reflections,” Dr Ginis explained.

After laboratory optimisation and validation, clinical performance of the instrument was investigated in a study that included 79 eyes with cataract (LOCS III grades one to five) and no other known ocular pathology, along with nine healthy eyes serving as a control group.

The mean straylight parameter measured with the optical device was about 0.9 log units for the control group and increased significantly with increasing LOCS III cataract grade.

“In our study, an eye with a LOCS III grade four-five cataract had about 10 times more light scattering than a healthy normal eye,” Dr Ginis said.

He reported that the optical measurements of straylight were not identical to psychophysical assessments obtained at the same cohort with a commercially available device (C-Quant, Oculus). However, the Pearson correlation coefficient (r=0.680) showed a strong positive association between the two variables.

Harilaos Ginis: ginis@um.es

IMAGE CAPTION

Image 1: Schematic layout of the optical device and the light source

(Courtesy of Harilaos Ginis PhD)