The Retinal Acuity Meter (RAM; AMA Optics Inc., Miami), previously known as the Illuminated Near Card (INC), was introduced in 1996 (Figure 1). This handheld device is used to assess macular function behind the media opacities caused by cataract or posterior capsular opacification. Preoperative potential acuity assessment may help surgeons give a more accurate estimate of postoperative acuity. In turn, predicting visual acuity may decrease the number of patients who are disappointed with their surgical results—or possibly avoid unrewarding surgeries.

The RAM device is especially useful in patients who have more than one cause of decreased vision. In a patient with cataract plus a macular disease (eg, diabetic retinopathy, epiretinal membrane, macular degeneration), it is often hard to determine whether the visual loss is due to the cataract alone or as part of the macular disease. The RAM allows for predictions of postoperative visual acuity and gives the physician useful data to provide patients with realistic expectations prior to cataract surgery or Nd:YAG laser capsulotomy.

The RAM technology combines three basic optical principles: a small aperture pinhole, correct visual angle, and bright illumination. The small aperture pinhole minimizes the effects of refractive errors and media opacities, and near correction is added to improve resolution. Multiple pinholes allow the patient to select the clearest view through the cloudy media.

To use the RAM, a pinhole aperture and a 2.50 D lens that focuses at 16 inches (40.64 cm) are placed over the eye being tested; the other eye is occluded. If refractive errors are present, this test should be carried out with the patient wearing the corrective lens. This portable battery-powered device is held 40 cm away from the patient, who then reads Snellen-like letters printed on a transparent disc through a brightly illuminated window. The lettering is gradually reduced in size until best acuity is achieved.

RAM VERSUS PAM
In our recent study comparing the RAM and the Potential Acuity Meter (PAM; Haag-Streit, Köniz, Switzerland),¹ we concluded that both devices were useful to help predict BCVA after phacoemulsification, however, the RAM was more likely to give an exact prediction of postoperative BCVA. This was true for patients with and without macular pathology. The RAM was more likely to overestimate, and the PAM was more likely to underestimate potential acuity.

Patients using the RAM may move their head and eye to see the eye chart through less opaque areas of the cataract, finding particular pinholes that allow for optimum clarity. The PAM is more dependent on the examiner, who must precisely direct the point source of light into the patient's pupil when sitting at a slit lamp. The patient may have to make minute head adjustments to find less opaque areas of the cataract to see through. The PAM only corrects for spherical refraction, but the RAM is able to correct for both spherical refraction and astigmatism.

The majority of patients subjectively found the RAM to be easier to use compared with the PAM. Many of our study patients complained of grittiness and jumping letters when viewing the PAM eye chart. Both devices showed a limited clinical capability in predicting postoperative visual acuity in patients with dense opacities and a visual acuity of 20/200 or worse. There appears to be a relationship between preoperative BCVA and accuracy of both the PAM and the RAM. This is consistent with the pinpoint charts of each test, as they may be better projected through a less-opaque media or promptly read by a better-functioning macula.

A wider use of potential acuity measurements may help surgeons give a more accurate estimate of postoperative acuity. This will help patients build reasonable postoperative BCVA expectations and decrease the number of surgeries performed without benefit to the patient. Alternately, patients with macular disease who seem to have little hope for improved vision may be candidates for cataract surgery based on potential acuity measurements.

Suzanna Airiani, MD, is Senior Resident at the Edward S. Harkness Eye Institute, College of Physicians and Surgeons, Columbia University, in New York. Dr. Airiani states that she has no financial interest in the products or companies mentioned. She may be reached at sa2057@columbia.edu.

Richard E. Braunstein, MD, is the Miranda Wong Tang Associate Professor of Clinical Ophthalmology at the Edward S. Harkness Eye Institute, College of Physicians and Surgeons, Columbia University, in New York. Dr. Braunstein states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +1 212 326 3320; fax: +1 212 326 3313; or reb10@columbia.edu.

1. Chang MA, Airiani S, Miele D, Braunstein RE. A comparison of the Potential Acuity Meter (PAM) and the Illuminated Near Card (INC) in patients undergoing phacoemulsification. Eye. 2006; 20:1345-1351.