Acuity Meter Research Articles

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 (U), 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 ≤ 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.

A Clinical Index for Predicting Visual Acuity After Cataract Surgery

We developed a clinical index for predicting postoperative visual acuity of cataract patients and cross-validated it using data from 182 patients aged 70 years and older. The index consisted of four statistically combined indicators: age, preoperative visual acuity, frequency of reading, and comorbidity. Validation of the index included comparisons to two standard technical instruments for measurement of retinal visual acuity. For the clinical index, 72% of predictions were accurate within one Snellen line of postoperative visual acuity compared to 37% using a laser interferometer and 33% using a potential acuity meter. Testing of the clinical index's external validity using data from 111 patients in a different ophthalmology clinic disclosed 61% of predictions accurate within one Snellen line.

A comparative study between the PAM and the laser interferometer in cataracts.

We conducted a prospective study on 35 consecutive eyes undergoing cataract extraction to compare the Guyton-Minkowski Potential Acuity Meter (PAM) and the Laser Interferometer (LI) in determining potential visual acuity. The eyes were divided into: group A, which had good visualization of optic disc details, and group B, whose media allowed only disc outline or less to be seen. We found that in group A eyes, both instruments were reliable (with accuracies of 94% for the PAM and 88% for the LI). However, in group B eyes (advanced cataracts), both instruments were unreliable (accuracies of 33% for the PAM and 53% for the LI). Interestingly, in a subgroup of high myopes (axial length greater than 29 mm) with moderate cataracts and poor visual acuties, both instruments were very reliable and helpful in determining how much of the vision loss was due to the cataracts. We therefore strongly recommend potential acuity testing in high myopes with moderate cataracts and poor visual acuity.

Potential Acuity Meter for Predicting Postoperative Visual Acuity in Penetrating Keratoplasty: A New Method Using a Hard Contact Lens

An irregular corneal surface degrades the optical transmission and limits the effectiveness of the potential acuity meter (PAM) in predicting postkeratoplasty visual acuity. The authors investigated the efficacy of using a temporarily placed hard contact lens to neutralize surface irregularities in conjunction with the PAM in predicting post-keratoplasty visual acuity. A prospective evaluation was performed on 40 keratoplasty patients with a mean follow-up of 10.4 months. Of 27 patients with corneas clear enough to permit them to read letters on the PAM chart, 17 (63%) had very accurately predicted visual acuities by this new method, compared to only eight patients (30%) with the PAM alone. Three patients had predicted visions better than final vision, but this was due to a concurrent cataract in two cases and chronic cystoid macular edema (CME) in the third case. This study indicates that temporarily placing a hard contact lens for use with the PAM can increase its accuracy in predicting final visual acuity after penetrating keratoplasty.

A Comparison of Visual Function Tests in Eyes with Maculopathy

Several recently developed tests of visual function, including the Potential Acuity Meter (PAM), laser interferometer (LI), white-light interferometer (WLI), blue field entoptic phenomenon, and focal electroretinogram (ERG) were compared in 81 eyes with clear media and known macular disease. The results indicate that the PAM, the LI, and the WLI overreact relative to Snellen acuity. Laser interferometric acuity values differed from Snellen acuity by at least 1.5 octaves in approximately 40% of all eyes, regardless of stimulus size (2, 5, or 8°). Similar results were obtained with the WLI. Agreement with Snellen acuity was better for the PAM, with 91 % of eyes falling within 1.5 octaves of Snellen acuity. Blue field and focal ERG results were categorized as normal or abnormal. While not producing Snellen equivalents, abnormal results from the blue field and focal ERG corresponded with poor Snellen acuity (<20/40) in 65% and 91 % of eyes, respectively. Assuming that media opacities do not prevent adequate retinal stimulation, the present results suggest that the PAM and focal ERG are the most reliable for evaluating macular function when maculopathy is present.

Visual Acuity Prediction Before Neodymium-YAG: Laser Posterior Capsulotomy

A laser interferometer (Retinometer) and the Potential Acuity Meter (PAM) was used to assess macular function before neodymium-YAG laser posterior capsulotomy in 40 patients. Although specificity was excellent with the PAM (91 %) and Retinometer (93%), sensitivity was limited to 42% and 33%, respectively. Diffuse posterior capsular opacification which precluded the delivery of light through a clear portion of the capsule was the most likely cause of the high false negative rate. A positive result on either test has good predictive value, reducing the chances of the capsulotomy being a failure by fourfold.

The influence of cataract types on potential acuity meter results

The records of 100 patients who had cataract surgery were reviewed to compare preoperative potential acuity meter (PAM) results with postoperative visual acuity. A PAM acuity was obtainable in 95 patients. In 82 of the 95 patients (86%), the PAM levels were within three lines of the outcome. Potential acuity meter results substantially lower (≤ four Snellen lines) than outcome generally occurred when posterior subcapsular (PSC) or PSC plus diffuse cortical or nuclear changes were present. We believe that the PAM projection can usually go around or through the nuclear sclerosis to give an accurate prediction. However, with PSC or mixed type, one may not always find a window in the cataract. Also, PSC or diffuse cortical cataracts may be particularly disruptive to the paracentral diffracted light that is an important factor in PAM acuity.

Potential Acuity Meter for Potential 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.

Instruments for Predicting Visual Acuity

A series of 54 eyes in 50 patients had preoperative predictions of postoperative visual acuity, using both a white-light interferometer (Lotmar Visometer) and a Snellen chart projector (Guyton-Minkowski Potential Acuity Meter). The predicted vision by each instrument was compared with the actual postoperative vision. Forty eyes in 36 of these patients, 25 with concurrent eye disease, had cataract extraction with intraocular lens implantation. Fifteen eyes in 15 patients, 11 with concurrent eye disease, had neodymium-YAG laser posterior capsulotomy. The Visometer gave more accurate predictions than the Potential Acuity Meter in cataract patients with open angle glaucoma, even with glaucomatous visual field loss, and in patients with a visual acuity of less than 20/400 due to advanced cataract formation.

Potential acuity meter to predict postoperative visual acuity

Thirty-three eyes were examined with the potential acuity meter (PAM) to determine preoperatively the expected visual acuity for patients undergoing cataract surgery. The preoperative visual acuity was compared to the best postoperative visual acuity. Although several patients had moderate macular degeneration as well as cataracts, there was an overall accuracy to within two lines of the best visual acuity in 96% of patients. There was a tendency to underestimate rather than overestimate postoperative visual acuity when these readings were in error. The instrument was only used if the cataract examined had some clarity. Older patients who were unsteady had difficulty performing the test.

Retinal Acuity Evaluation with the Potential Acuity Meter in Glaucoma Patients

The potential acuity meter (PAM) is designed to evaluate retinal acuity in the presence of media opacities. We looked at patients with glaucoma but with clear media, and compared best corrected visual acuity with PAM results to see if they produced comparable results. Sixty eyes in 38 glaucoma patients and 20 eyes in 10 normal ocular patients were evaluated. Our results indicate that PAM visual acuity is a reliable indicator of Snellen visual acuity in normal eyes, in eyes with mild to moderate glaucomatous damage, and when PAM visual acuity measurements were better than 20/60. However, when visual field loss is severe and when PAM visual acuity readings were worse than 20/60, the correspondence between these and Snellen visual acuity was erratic. Poor PAM results will not correlate with postoperative visual acuity in patients with advanced glaucoma and cataracts.

Pre-keratoplasty Potential Acuity Evaluation: Laser interferometer and Potential Acuity Meter

Twenty-three patients who underwent penetrating keratoplasry were evaluated preoperatively for potential retinal acuity utilizing the Randwal Laser Interferometer and the Mentor Potential Acuity Meter. When compared with Snellen visual acuity during the early postoperative period (1–6 months), both instruments were useful as qualitative predictors of maculae function when used in the presence of mild to moderate corneal edema. The laser interferometer was somewhat more accurate in the severe cases of corneal edema.

Potential Acuity Meter Using a Minute Aerial Pinhole Aperture

A new instrument allows accurate measurement of retinal visual acuity behind mild to moderate cataracts. Mounted on a slit lamp, the Potential Acuity Meter projects a Snellen visual acuity chart into the eye via a narrow beam of light converging to a minute aerial aperture only 0.15 mm in diameter. The examiner aims the narrow beam through “windows” in the cataract, avoiding blockage or scattering of the light that would otherwise occur. In 47 cataractous eyes having best preoperative visual acuity of 20/200 and better, the postoperative visual acuity was predicted to within three lines in 100% of cases, and to within two lines in 91%. With a successful result from cataract surgery defined as postoperative vision of 20/40 or better, the prediction of success with the Potential Acuity Meter was correct in 95% of cases.

Predicting acuities in capsulotomy patients: interferometers and potential acuity meter.

Using the Lotmar moiré fringe interferometer and the potential acuity meter, I predicted the postoperative Snellen visual acuities in 30 implanted eyes that required secondary capsulotomies. The Lotmar interferometer was within one line of the postoperative visual acuity in 29 eyes (96.6%); the potential acuity meter prediction was within one line in 10 eyes (33.3%). An earlier study defined seven clinical conditions that produced false positive results with the laser interferometer. The same results occurred with the Lotmar interferometer. When the potential acuity meter was used, six of the seven conditions produced false positive results.

Takata Interferometric Device

To the Editor. —Not long ago, my colleagues and I published a brief article in theArchivesdescribing the use of the Takata Interferometric Acuity Meter in early detection of possible demyelinating disease. The article described the use of a Takata Interferometric Device for this purpose (Archives97:76-78, 1979). There is no question about the validity of our findings; rather, we have discovered that the particular Takata instrument available to us was improperly wired and literally put out a far more intense beam than the instrument is rated to provide. Since then, that instrument has failed and in making repairs we have discovered the fault. At issue was the fact that it had been wired for a voltage system different than that in use in the United States. As this was the first unit delivered to this country, this is a reasonable error. At any rate, the issue is that

A Semi-automated Instrument for Determination of Acuity Threshold

A device has been constructed that permits rapid, repeatable measures of visual acuity while minimizing many of the patient and examiner errors in subjective acuity testing. The Baylor acuity meter utilizes digital logic circuitry to implement a carefully controlled psychophysical "staircase" testing procedure in a small portable unit. Comparisons of the acuity meter with conventional measurement techniques on 51 subjects yield correlations of +.74 and +.81. A test-retest correlation of +.96 was found.