Abstract
Purpose: :
Forward light scatter is the major cause of visual loss in patients developing posterior capsule opacification (PCO). The purpose of this study was to develop a system for forward light scatter measurement in an in vitro model of PCO to better understand its effect on forward light scatter and to relate it to PCO grading using retroillimunation images.
Methods: :
A collimated and spatially filtered 543nm He-Ne laser, whose Gaussian beam profile was "top-hatted" to produce a uniform beam of diameter 4mm, was passed vertically through the samples. A detector comprising an inverse spatial filter arrangement with a photodetector behind the pinhole was moved through ±17.5 degrees (resolution 1' arc) either side of the scatter function peak. This detector arrangement integrates the scatter for any given angle over the 4mm diameter illuminated region of the sample in a similar fashion to the in vivo eye. Posterior lens capsule was dissected from human cadaver eyes and cultured for different amounts of time to produce varying severity and coverage of PCO. Lens capsules were photographed on a phase contrast microscope, measured for forward light scatter and then cleaned by causing osmotic injury to the LECs before measuring again. Micrographs of the central 4mm of the capsule were subjected to PCO grading using the POCOMAN software prior to cleaning.
Results: :
Forward light scatter was quantified by the area under the scatter function (AUSF) for N=17 human lens capsules. The coefficient of variability for AUSF in lens capsule with PCO was 5.1%. The average value for the AUSF for opacified lens capsules was 0.164 ± 0.101µA deg. and 0.027 ± 0.013µA deg. for cleaned lens capsules (both mean ± SD). The average POCOMAN grading was 1.60 ± 0.63 (mean ± SD) with a range of 0.05 to 2.62 and a SD of 0.09 when testing repeatability on a single sample. The difference in AUSF for opacified and cleaned lens capsule was used as a measure of forward light scatter caused by PCO alone. Correlation of this value with the POCOMAN grading gave an R2 value of 10.6% which was not statistically significant (P=0.201).
Conclusions: :
Subjective analysis of area covered and severity of PCO from phase contrast images using the POCOMAN software does not relate to forward light scatter. Experiments should be repeated with both retroillumination and slit-lamp graded images of PCO. Such in vitro measurements will help determine the link between forward light scatter and clinical methods of measuring opacification.
Keywords: posterior capsular opacification (PCO) • clinical laboratory testing