Retinal acuity evaluation with the potential acuity meter in glaucoma patients

Potential acuity pinhole: a simple method to measure potential visual acuity in patients with cataracts, comparison to potential acuity meter

OBJECTIVE

To describe the potential acuity pinhole (PAP) test and compare its accuracy to the potential acuity meter (PAM) in predicting visual outcome after cataract surgery.

STUDY DESIGN

Prospective case series.

PARTICIPANTS

A total of 56 preoperative patients with cataracts participated.

MAIN OUTCOME MEASURES

Accuracy of predicting postoperative distance visual acuity was measured.

METHODS

Lines of inaccuracy were calculated by subtracting actual postoperative best-corrected distance visual acuity (BCVA) from predicted values. Variables analyzed were method of prediction, preoperative BCVA, and preoperative spherical equivalent.

RESULTS

The PAP test predicted visual outcomes within 2 lines in 100%, 100%, and 56% of eyes with preoperative BCVA of 20/50 and better (group 1), 20/60 to 20/100 (group II), and 20/200 and worse (group III), respectively. The PAM predictions within 2 lines for the same groups were 42%, 47%, and 0%, respectively. Mean lines of inaccuracy of PAP predictions were 0.83, 1.11, and 3.50 lines for groups I, II, and III, respectively. Mean lines of inaccuracy for PAM predictions were 2.50, 2.68, and 6.22 lines for the same groups. Differences in lines of prediction between PAM and PAP were 1.67 (P = 0.004), 1.58 (P = 0.0002), and 2.72 lines (P = 0.0001) for groups I, II, and III, respectively. There was no statistically significant correlation between PAP predictions and preoperative myopic spherical equivalent.

CONCLUSIONS

The PAP test is a simple, inexpensive, and relatively reliable method to estimate visual outcome after uncomplicated cataract surgery in eyes with no coexisting disease. It is less accurate in patients with preoperative BCVA worse than 20/200. It appears to be more predictive than PAM.

Effects of posterior segment disorders on oscillatory displacement thresholds, and on acuities as measured using the potential acuity meter and laser interferometer

Oscillatory displacement thresholds (ODTs) were measured in 67 subjects with clear ocular media, but known posterior segment disorders. The ability of these thresholds to assess reduced visual function, as quantified by visual acuity deficits, was compared with that of the Potential Acuity Meter (PAM) and the Rodenstock Retinometer (RR). ODTs were found to be sensitive to acuity deficits which were retinal/neural in origin. Despite the fact that interferometric acuities are, unlike ODTs, a measure of resolution, the RR proved no more accurate in assessing the level of letter acuity which existed than did ODT measurement. As would be expected, the PAM provided for the most accurate means of assessing non-optical visual acuity deficits. However, the PAM proved to be less useful in eyes with: very poor levels of acuity, and certain anomalous conditions. The results have implications for the relative ability of each of the three tests to identify reduced visual function behind cataract.

Risk of postoperative visual loss in advanced glaucoma

The incidence of sudden visual loss after an intraocular procedure in patients with glaucoma and visual field defects has been disputed for over a century. We examined the risk of sudden visual loss associated with trabeculectomy in glaucoma patients with advanced visual field defects. Fifty-four filtering operations performed on 44 patients were reviewed. All patients had visual field defects encroaching on or splitting fixation, a visual acuity of 20/100 or better, and a follow-up period of at least two months. Thirty-one of the 54 preoperative visual fields (57%) disclosed a fixation-splitting defect. Sudden visual loss was not observed in any patient during the two-month postoperative period. These findings suggest that the incidence of sudden postoperative visual loss is lower than previously reported.

Predictions of outcomes from cataract surgery in elderly persons

To determine how well visual outcomes of cataract surgery can be predicted from acuity estimations by visual instruments and an ophthalmologist, the authors compared predictions of postsurgical visual acuity with the measured acuity at 4 months in 82 elderly persons. Comparisons were made between the potential acuity meter (PAM), laser interferometer (LI), and an ophthalmologist, who predicted the final vision before surgery using screening visual information, including PAM, LI data, and results of the patient's examination. Neither instrument alone was successful in predicting postsurgical acuity +/- 1 contiguous Snellen chart line (bivariate correlation [r] = 0.03 for PAM and 0.07 for LI). The ophthalmologist was the most accurate predictor of acuity within 1 line (r = 0.41, p less than or equal to 0.001). These results indicate that the PAM and LI did not independently predict postsurgical vision in elderly cataract patients, but results of a clinical examination markedly improved the accuracy of predictions.

Potential acuity meter for predicting visual acuity after Nd:YAG posterior capsulotomy

We studied 30 patients with opacifications of the posterior capsule to determine if the potential acuity meter (PAM) could accurately predict final visual outcome after Nd:YAG discussion. The final visual acuity was within one line of the PAM prediction in 22 of 30 patients (73%), better by two or more lines in seven patients (23%), and worse in one patient (4%) by two lines. Although in thicker capsules the final acuity was occasionally better than the PAM prediction, the rates of false negative and false positive predictions were very low. Mild cystoid macular edema (3 patients), age-related macular degeneration (3 patients), intraocular lens status, and level of initial acuity did not diminish PAM accuracy. The PAM effectively predicts final visual acuity after YAG posterior capsulotomy, when used in a patient, unhurried manner.