History of Potential Vision
Why measure Potential Vision in eyes with cataract?
1. To identify eyes with POOR vision prognosis.
2. To identify eyes with GOOD vision prognosis that appear abnormal on examination.
Potential vision testing is the only proven method that predicts the vision outcome in eyes with cataract. Examining the eye is simply can not enough predict the potential visual outcome. Published expert opinions are “All clinicians know that the appearance of the macula can be misleading: one that looks highly irregular may have excellent visual potential.” Samuel Masket, MD (6) and “The anatomic appearance of the macula on biomicroscopy or OCT does not always correlate well with macular function.” Jay S. Pepose, MD. PhD.(6). This is echoed in the Preferred Practice Plan of the American Academy of Ophthalmology, “Biomicroscopy and the ophthalmoscopic examination of the macular region do not necessarily predict macular function when the macular is abnormal.”
The Power of Forecasting
Forecasting attempts to reduce the uncertainty of what is to come and this has turned man to religion and science for direction. In the realm of science, it was gambling that provided the impetus that lead to the development of the probability theory, which was fueled by the desire to increase the odds of winning. The probability theory forms the basis of statistics and is widely applied in all fields of science. The development and the implementation of the probability theory can be traced to great scholars, such as, Blaise Pascal (1623 –1662), Pierre de Fermat (1601 [or 1607] –1665), Christian Huygens (1629 –1695), Jacob Bernoulli (1654-1705), Abraham de Moivre (1667-1754), Pierre de Laplace (1749-1827, A. Kolmogorov (1903 – 1987), Peter L Bernstein (1919 – 2009), and others.
Peter L. Bernstein said, “When you think about risk, it essentially says we don’t know what is going to happen.” Relating this concept to cataract surgery, if you know what the vision outcome is going to be, risk of a poor outcome is reduced. In large part, the unpleasant surprise of poor vision following surgery due to undiagnosed conditions can now be avoided by potential vision testing with the Retinal Acuity Meter (RAM), the only potential vision test found consistently accurate.
Vision Forecasting Evolution
Patients facing cataract surgery usually assume a favorable outcome particularly when their doctor informs them of no worrisome findings on the “Comprehensive Eye Examination”. Never the less, unpleasant poor outcomes occur, which could have been predicted prior to surgery by adding potential vision testing to the pre-op analysis. Forewarning of a less than optimum outcome can change a potentially unpleasant surprise into a celebration for only a small but predicted improvement in vision.
In the entire field of medicine, the functional result of surgery has only been accurately predicted for vision. A cataract blocks the eye from seeing as well as the retina is capable of seeing. To reveal the potential of the retina, a variety of potential vision testing techniques have been developed. Some of the early potential vision tests were inaccurate, improvements have been made and now the ability to recover youthful vision following cataract surgery can be determined with great accuracy prior to embarking on surgery. Yes, a preoperative potential vision test can determine in most cases how visually rewarding cataract surgery will be for the patient.
Tests measuring the function of the eye were introduced in the 1980s, the most popular being the Potential Acuity Meter (PAM) and interferometers. Medicare and some insurance companies reimbursed for testing, but this came to an abrupt end in 1993. A literature review article appearing in Ophthalmology in 1993 (100:150S-177S) concluded that current potential vision tests failed to detect poor surgical outcomes. In that review article, 40 published articles were reviewed which included studies involving the Potential Acuity Meter (PAM) and interferometers. None of the studies support the use of potential vision testing to detect poor surgical outcomes. If anything, they suggested that the utility of these tests was limited to cases in which the cataract was not dense. With factual basis, it was stated, "In such situations, the ophthalmologist can usually visualize the fundus and determine from clinical examination whether cataract surgery is likely to improve vision". The message is loud and clear; for a potential vision test to be valuable, it must be able to consistently detect poor surgical outcomes in eyes with and without co-morbid disease.
Unfortunately, the above statement “In such situations, the ophthalmologist can usually visualize the fundus and determine from clinical examination whether cataract surgery is likely to improve vision” is inaccurate and misleading and has allowed many surgeons to avoid testing potential function by any means and to rely solely upon the fallible examination of structure for making surgical decisions involving function. The eye examination has never been shown to predict function! As a result of this faulty line of reasoning, there is no requirement for the doctor to demonstrate the potential for vision improvement prior to cataract surgery as stated in Medicare National Coverage Determinations Manual: Chapter 1, Part 1 (Sections 10 – 80.12). The manual states, “where the only diagnosis is cataract(s), Medicare does not routinely cover testing other than one comprehensive eye examination”. The comprehensive eye examination includes a non-mandatory potential vision testing requirement. Because potential vision testing can not be billed separately, potential vision is rarely determined.
In Summary, Medicare prerequisites for cataract surgery are (1) evidence of vision acuity loss and (2) an eye examination. A potential vision test is not a prerequisite. The omission of potential vision testing in the Medicare guidelines leads to (1) denying surgery in eyes that appear abnormal upon examination but have good function and (2) approving surgery in eyes that look normal but have poor function. The frequency of these cases is unknown. However, in a survey by AMA Optics, Inc. of 71 physicians using the RAM® disclosed (1) 75% of the physicians found the RAM® averted poor surgical outcomes (cases allowed by Medicare guidelines based upon the vision loss and an eye examination) and (2) 92% found that "inoperable cases" based on the eye examination actually had good potential visual function and benefited from surgery.
Current Status of Potential Vision Testing
The RAM® (Retinal Acuity Meter) was introduced after the review article of 1993 that emphasized the unpredictability of potential vision testers to predict poor outcomes. The RAM(1-4) is proven to accurately predict poor and good outcomes. One article(3) also found the PAM (Potential Acuity Meter) highly predictive in eyes with and without co-morbid disease, but in a later article(5) the PAM and the Visometer (interferometer) were both found to be inaccurate in eyes with cataract. PAM predictions have varied greatly among published studies. The PAM is known to be difficult for patients and requires examiners with expertise, these factors may explain the irratic reported accuracy of this device.
The RAM® is the only clinically proven potential vision test to consistently predict poor outcomes when visual acuity is 20/200 or better. No study has found the RAM to be less than an excellent predictor of post-operative visual acuity. In four published peer-reviewed articles(1-4) totaling 186 eyes, the mean predictability of the post-op vision to within 2 lines of letters was 96% for the RAM.
To quote Bret Fisher, MD(7), “I find that the Retinal Acuity Meter, which helps to predict postoperative vision, is very helpful in identifying hidden issues”.
1. Hofeldt, A.J.: Illuminated near card assessment of potential visual acuity. J Cataract Refract Surg. 22:367-371, 1996.
2. Hofeldt, A.J. and Weiss M.J.: The illuminated near card assessment of acuity in eyes with cataract. Ophthalmology 105, 1531-6, 1998.
3. 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.
4. Park, JI, Oh, SH, Kim, JH, Moon, SW, Lee, DH: The Potential Role of the Retinal Acuity Meter For Predicting Visual Outcome after Cataract Surgery. J Korean Ophthalmology Soc. 2007 Jul;48(7):898-904,
5. O Reid, DAL Maberley and H Hollands: Comparison of the potential acuity meter and the visometer in cataract patients. Eye (2007) 21, 195–199.
6. Macular Function. CRST Nov/Dec 2010, pp. 43-44.
7. Managing Postoperative Dissatisfaction. Supplement to CRST Oct 2013.