Correlation between the measurement of posterior capsule opacification severity and visual function testing.

Purpose: To develop software to measure the severity of posterior capsule opacification (PCO) using analysis of retroillumination images and to correlate the results with clinical evaluation of PCO severity and visual function.

Setting: Department of Physics, King's College, and Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

Methods: A technique for calculating PCO severity was developed based on calculating the variance of intensity by transforming retroillumination images to a similar mean intensity. The computer-derived severity was compared to grading of clinical severity by 3 independent observers using a library of 100 retroillumination images ranging from clear posterior capsules to very severe PCO. The computer results were also compared with the following other current methods of measuring PCO: Evaluation of Posterior Capsule Opacification (EPCO), POCOman, and Automated Quantification of After-Cataract. A further 35 images were used to compare the results of computer-derived severity with the results of visual function analysis (high-contrast acuity, 100%; low-contrast acuity, 9%) using the Early Treatment Diabetic Retinopathy Study chart, contrast sensitivity testing using the Pelli-Robson chart, and glare assessment using the van den Berg straylight meter.

Results: The severity scores showed a good correlation with clinical severity scores for the library of images (r=0.86) and with severity scores using POCOman and EPCO (r=0.85 and r=0.81, respectively). The correlations with visual function tests were also good, with low-contrast visual acuity (9%) showing the best correlation (r=0.87).

Conclusion: Variance in intensity of PCO was successfully used to calculate the severity of PCO.