Image analysis of Scheimpflug negatives. Comparative quantitative assessment of the film blackening by area planimetry and height measurements of linear densitograms

Abstract

Evaluation of various long-term studies on changes of different lens opacities, as had been rendered possible by microdensitometric image analysis of the film blackening of Scheimpflug photographs, showed that only in a few special cases an extension of the opacification to adjacent lens layers is to be expected within the observation period of 2-3 years. This means that one of the reasons for evaluating the densitometer curve by area planimetry is no longer valid and may be neglected. A further advantage of the measurement of film blackening by height evaluation (height of densitometer deflection above baseline, i.e., noise level) is the fact that it is highly independent of subjective factors and, therefore, ensures a far better reproducibility with respect to data acquisition. The results of both evaluation procedures, obtained by evaluating the identical film material (2 photoexaminations) of 14 volunteers, are presented, and the advantage of height measurement as opposed to planimetry is demonstrated.