Devereux C, Rando Borth A, Wagstaff C, Story I. Potential acuity meter results in cataract patients. Clin Exp Ophthalmol 2000;28:414–418.
Original study reprint requests: Catherine Devereux, School of Orthoptics, La Trobe University, Bundoora, Victoria 3083, Australia.
To determine the ability of the potential acuity meter (PAM) to predict potential visual acuity through lenticular opacities in a group of patients with cataracts without significant other ocular disease.
A prospective study.
Eight different A-Scan and Primary Care Clinics in Melbourne, Australia.
This prospective study undertook PAM measurements on each eye of 84 subjects during preoperative hospital visits to either A Scan or Primary Care clinics. PAM results were compared to best corrected-visual acuity findings obtained at least 6 weeks after cataract extraction.
Preoperative PAM measurements and postoperative best-corrected Snellen visual acuity.
Comparison of PAM result to visual outcome showed poor correlation (rho = 0.41, p = 0.0005). Using predictive estimates, 49% of subjects' PAM results underestimated visual outcome as determined by a difference of greater than 2 Snellen acuity lines in these results. Factors such as preoperative vision level, cataract type, and pupil dilation did not significantly influence the predictive power of the PAM. Preoperative pinhole results were also correlated with visual outcome (rho = 0.42, p = 0.0006). Vision in the fellow eye of subjects with 6/9 or better was correlated to the PAM, result indicating a moderate to good predictive power in “normal” eyes.
PAM results were considered to be poor for a clinical test. The results of this study indicate that this instrument has only a limited usefulness as part of the standard preoperative examination in patients undergoing cataract extraction, with a moderate to good correlation in normal eyes and a poor to moderate predictive power for visual outcome in patients with cataract alone.
Twenty years ago when the typical patient undergoing cataract extraction with intraocular lens implantation was 75 years of age with a preoperative visual acuity no better than 20/200, there was little necessity for an accurate estimate of postoperative visual acuity. Times have changed. With improvements of outcomes came changes in surgical indications as well as patient expectations. The risk:benefit ratio of cataract extraction, predicated on the resultant visual acuity after surgical intervention, makes the accurate estimate of postoperative visual acuity an imperative. Although careful history taking and ophthalmic examination are what we do best, from time to time the presence of concomitant retinal disease confounds our clinical expertise. One of the instruments available to aid us in this clinical decision-making process is the PAM. A study by Datiles et al. 1 in 1987 suggested that the PAM underestimated final visual outcomes. This article corroborates those findings.
It was known that the PAM made errors when making predictions in eyes with macular disease, a visual field-cut through fixation, or severe glaucoma. 2,3 In addition to these known weaknesses, this prospective study indicates that the PAM was equally inaccurate in the following circumstances.
- In severe and moderate cataracts.
- In different types of cataracts.
- In dilated and undilated patients.
The authors suggest that the accuracy of the PAM is no greater than that of the pinhole test, which is faster, cheaper, and easier to perform. Based on my own clinical experience, I suspect that most of us who own a PAM would agree with that conclusion.
1. Datiles MB, Edwards PA, Kaiser-Kupfer MI, et al. A comparative study between the PAM and laser interferometer in cataracts. Graefes Arch Clin Exp Ophthalmol 1987; 225:457.
2. Guyton DL. Prediction of postoperative vision in cataract patients. Clin North Am 1989; 2:431.
3. Ing MR. Potential acuity meter to predict postoperative visual acuity. J Cataract Refract Surg 1986; 12:34.