In each case, it is assumed that a cataract is present for which extraction is indicated, independent of the glaucoma. However, the visual significance of the cataract is often difficult to determine in an eye with both a cataract and glaucoma, in which it is hard to know how much the glaucoma is contributing to the reduced vision.
Several instruments have been developed to help predict the anticipated postoperative visual acuity. One focuses a miniaturized Snellen visual acuity chart on the retina (Potential Acuity Meter or PAM) whereas others project stripe patterns from either a laser or white light (Visometer) source. PAM measurements do not always show good correlation to postoperative results (5), particularly for dense cataracts (6).
In one study, the Visometer gave more accurate predictions than the PAM in cataract patients with open-angle glaucoma, even with glaucomatous field loss (7). In other studies, the PAM was accurate when the glaucomatous damage was mild-to-moderate and the postoperative visual acuity was 20/40 to 20/50 or better, whereas the results with advanced visual field loss or a worse postoperative vision were not reliable (8,9). Automated perimetry was found to be useful in predicting whether the vision would be better or worse than 20/40. Combining this with the use of the PAM further increased the predictive value (9).
When it is decided that cataract surgery is needed, the selection of the specific surgical approach is based primarily on the status of the glaucoma.
