Lens opacity as a predictor of visual field impairment due to cataract. The contribution of cataract to the decrease of visual field in patients with glaucoma is difficult to ascertain. To attempt to quantitate the change in visual field due to cataract, we examined 27 eyes of 26 patients before and after cataract extraction. The examination consisted of measurement of best refraction with visual acuity, visual field testing with the pupil dilated, measurement of lens opacity, determination of the intraocular pressure, and evaluation of the character of the cataract before surgery and of the posterior capsule after surgery. The results reaffirmed the detrimental effect that cataract may have on the visual field but also showed that the heterogeneity of cataracts limits the usefulness of the lens opacity meter in quantitating the extent of visual field loss due to cataract. 