Diagnosis of early glaucoma with flicker comparisons of serial disc photographs

We evaluated flicker comparison, a technique for detecting differences in serial fundus photographs. Serial optic disc photographs and computerized threshold visual fields were obtained every 3 months for an average of 40 months in 131 eyes of 81 patients with elevated intraocular pressure and normal visual fields. Two serial monophotographs were projected, optically aligned, and superimposed; analysis was done by alternately viewing first one and then the other image. We found flicker analysis of serial disc photographs to provide results which were closely correlated with those of computerized threshold perimetry. Thus, of those 12 eyes which developed field defects, eight showed definite change and two showed highly suspected change in optic disc configuration. Only two eyes showed a definite alteration in optic disc anatomy without the development of field loss, and field defects appeared in only one of 109 eyes in which there was no change or suspected change on flicker comparison. The flicker method was more sensitive than conventional nonflickered comparisons, but changes could usually be seen also with conventional inspection once they had been detected by the flicker method. Our findings suggest that flicker analysis may offer a considerable improvement over current standard methods of analyzing serial photography and may be a useful complement to routine perimetry. However, this method requires special equipment; requires that the photographs be similarly centered; and is time-consuming. Alignment of photographs by means of computerized image analysis techniques could make the method clinically practicable.