Performance of two films for densitometry of retinal photographs

The relative performance was determined of two different photographic films (Kodak Panatomic-X and Kodak Technical Pan) for densitometry readings from retinal photographs of patients who had or were suspected of having glaucoma. The raw data from the two films were significantly different. The high contrast film was particularly sensitive to external variables; however, when normalised in terms of the standardised deviation, the data from the two films were comparable (P < 0.005). We also measured the pattern of nerve fibre layer loss using digital image analysis of red-free photographs of normal, ocular-hypertensive, glaucoma-suspect and glaucomatous eyes. Several mathematical techniques were used to characterise the data from each eye and then to compare these data to the mean photographic density of the normal eyes. Results showed that it was possible to separate normal eyes from glaucomatous eyes. The highest sensitivity achieved was 100% for right and 88% for left eyes, and the highest specificity was 100% for both eyes.