QUANTIFICATION OF CATARACT USING THE RETROILLUMINATION MODULE OF THE NIDEK EAS-1000 ANTERIOR SEGMENT ANALYSIS SYSTEM

Cortical and posterior subcapsular (PSC) cataracts are best quantified by a retroillumination method. We have used the Nidek EAS-1000 camera system to document such cataracts and have investigated how variabili ty from operator input may be minimised when analysing retroilluminati on photographs. We then used our method to quantify the reproducibilit y of (i) image analysis and (ii) the system as a whole. A total of 99 eyes from 70 patients with either cortical or posterior subcapsular ca taracts were photographed twice at one session. The first set of image s was analysed twice and the second set once only. Cataract was classi fied as a density at least 14 grey scale units (cct) greater than clea r lens. The brightest 2% was excluded from analysis as it corresponded to the first Purkinje image of the fixation light. The reproducibilit y and 'noise' of the analysis method were assessed by calculating the correlation coefficient (r(2)) and standard deviation (SD) of the diff erences obtained for the two analyses of the first set of images. Repl icate analysis from the digitised images was excellent (r(2)=0.99, SD of the opacities differences +/- 1.74%). For the analysis of the syste m as a whole, replicate photographs showed a greater variability but s till good: r(2)=0.94 and the SD of the differences +/- 4.69%. The repr oducibility of the system is limited by variability of the image captu re rather than by the image analysis methods.