PULFRICHS PHENOMENON IN UNILATERAL CATARACT

Aims-To determine whether unilateral cataract causes a pathological Pu lfrich's phenomenon. Methods-29 subjects with unilateral cataract and contralateral pseudophakia were assessed on their ability to perceive the Pulfrich phenomenon. Using a computer generated pendulum image, an d graded neutral density filters, a series of forced choice trials wer e performed in which the subject was required to describe the directio n of any apparent pendulum rotation. A pathological Pulfrich effect wa s said to occur when apparent rotation was perceived in the presence o f a zero strength neutral density filter. The size of any pathological Pulfrich effect which was present was quantified by neutralising the perceived pendulum rotation with neutral density filters of varying st rength placed before the better seeing eye. Results-20 out of 29 subje cts were able to perceive apparent pendulum rotation when uniocular fi ltering was performed. In the group (n=12) which was tested both befor e and after cataract extraction with intraocular lens implantation, a statistically significant pathological Pulfrich effect was demonstrate d preoperatively, compared with a group of normal control subjects. Th is effect was abolished after cataract extraction (p=0.009). The media n size of the effect was equivalent to a 0.25 log unit neutral density filter over the non-cataractous eye. The subjects who were unable to perceive the Pulfrich phenomenon at all had a significantly greater di fference in the visual acuity of each eye (p=0.045) and significantly worse stereoacuity than those who were able to perceive the effect (p= 0.002). Conclusions-Unilateral cataract can cause a pathological Pulfr ich phenomenon. This finding may explain why some patients with unilat eral cataract complain of visual symptoms that are not easily accounte d for in terms of visual acuity, contrast sensitivity, or stereoacuity .