Purpose: To determine the limits of usefulness of the potential acuity meter (PAM) and the laser interferometer (LI) in determining potential visual acuity in various severities and types of cataracts.
Methods: The study included 48 patients (67 eyes) who were undergoing cataract surgery and who had PAM and LI tests. The 67 eyes were grouped into (1) eyes with cataracts only (45 eyes) and (2) eyes with cataracts and other ocular diseases (22 eyes). Group 1 eyes were subdivided into two groups according to their Lens Opacities Classification System II (LOCS II) grading: 1a eyes (moderate cataracts) had an LOCS II grade of nuclear opalescence (NO) < 4 and cortical opacity (C) < 5 and posterior sub-capsularcataract (P) < 4, and group 1b eyes (severe cataracts) had an LOCS II grade of NO = 4 or C = 5 or P = 4. The accuracy of the PAM and LI was estimated separately for each group.
Results: For moderate cataracts, the accuracy of the PAM was 100% and of the LI was 92%. For severe cataracts, the accuracy of the PAM was 52% and of the LI was 79%. Both instruments tended to underestimate visual outcome more in eyes with posterior subcapsular cataracts. For eyes with other ocular diseases, the LI tends to overestimate the probable visual outcome more than the PAM, especially in patients with poor retinal function.
Conclusions: Several factors such as preoperative visual acuity of 20/200 or worse, the type and severity of the cataract, and coexisting retinal disorders may affect the accuracy of the PAM and LI tests, and these should be considered when interpreting predicted vision, especially in preoperative counseling of patients.