Retinal acuity meter predicts potential vision, assesses macular function

November 1, 2005

While fluorescein angiograms and optical coherence tomography can assess structure, the retinal acuity meter looks at function.

The Retinal Acuity Meter (RAM) (AMA Optics Inc., Miami Beach, FL) is a new potential vision tester that is proving to be a consistently accurate method of predicting the postoperative visual acuity of patients undergoing cataract surgery or YAG laser capsulotomy.

A soon-to-be-submitted study also indicates that the RAM is effective in determining macular acuity, said Michael J. Weiss, MD, PhD, associate clinical professor of ophthalmology, Edward S. Harkness Eye Institute, Columbia University College of Physicians and Surgeons, New York, who participated in earlier studies of the RAM and uses it in his practice.

The RAM was approved by the FDA in 1996 and has been used in clinical research studies for a number of years, although significant commercial marketing of the device did not begin until earlier this year.

RAM implementation

To use the RAM, a pinhole aperture and a +2.5-D lens that focuses at 16 inches are placed over one eye and the other is occluded. The RAM is held at 16 inches, and the patient reads letters in a brightly illuminated window. The lettering is progressively reduced in size until best acuity is achieved.

The device is especially useful in patients who have more than one cause of decreased vision, Dr. Weiss said, such as both cataract and macular degeneration, and the physician needs to determine whether the patient would benefit from cataract surgery.

"Because the RAM is patient and doctor user-friendly, it is easy to make that assessment," Dr. Weiss said. While fluorescein angiograms and optical coherence tomography can assess structure, the RAM looks at function, he explained, and that is the predictive measure that matters most in patients with comorbid disease.

The RAM would also be beneficial in patients who have a posterior capsule and macular gliosis. The question of whether to perform a YAG capsulotomy to improve vision can be easily answered by using the RAM to test potential acuity, Dr. Weiss said.

Obtaining these reliable predictions of acuity helps reduce the risk of poor outcomes and creates positive, realistic expectations for patients prior to cataract surgery or YAG laser capsulotomy, said Tom Minero, director of sales and marketing for AMA Optics.

"For patients, it's also very helpful," Dr. Weiss said. "If they can see better with this device, they suddenly recognize the difference between their current vision and what it would be if they didn't have a cataract or if they had their posterior capsule opened up. That encourages them to go along with the recommendations to have whatever operation is needed."

The RAM is likely to supersede earlier devices, such as the Potential Acuity Meter (PAM), that also were used to predict acuity. This is in part due to the user-friendly design of the RAM, Dr. Weiss said.

"Most patients cannot figure out how to use the PAM. It is a very difficult instrument to use," Dr. Weiss said, adding that he has played the role of a patient and also had trouble with the device.

"It's big and clunky, and on top of that it may not be as accurate as the RAM," he added.