First, let me share a clinical pearl with you. It comes from our weekly case conference earlier today in which our therapists and docs sit around a table and brainstorm about patients and different clinical ideas. Chances are you’re familiar the Macdonald Form Field Recognition Cards, readily available through OEPF.
There are other variations of this card, principally the Lora Card (made by vision therapist extraordinaire Lora McGraw) and the Rothman Card (made by our good buddy, Dr. Stuart Rothman). Today we were talking about a patient who becomes overly central when doing the procedure and has a very tough time maintaining awareness of and clarity in the periphery. We reminded one another that we have acetate overlays that we use for the overhead projector, but can use them in the same manner of Macdonald Form Field Cards. We happen to make our own versions of them, and here is one:
So … we pulled it out during case conference, and simply held it like you would have a patient hold it the Harmon Distance. The difference between the letters on an opaque card or on a white sheet, as compared to their visibility and recognition with the acetate was obvious! Try it yourself at home (or in the office) – and you should notice that it’s much easier to keep your periphery open when the periphery is open.
OEP has a two volume set on The Collected Works of Lawrence Macdonald, and in Volume 2, pages 333-4 emphasizes the importance of relaxation, lessening the intensity, looking soft or easy and so on. To my knowledge, Dr. Macdonald never gave a detailed explanation about how he derived the scaling for the letter sizes or their spacing. Many moons ago, I had the pleasure of reviewing some of these concepts with one of our SUNY residents, Dr. Marie Marrone, who wrote a nice paper on the subject of peripheral awareness.
Does this chart look familiar?
It’s from the work of Stuart Anstis, Ph.D., an experimental psychologist from Ontario, Canada (and subsequently of UCSD) who worked out a form recognition chart very similar to what Larry Macdonald derived empirically. Due to decreasing cone density in the retina and the limits of resolution, letters have to be made larger when viewed eccentrically. Anstis notes that each letter was arbitrarily made 10 times its threshold height, so each letter is about equally easy to read when the center of the chart is fixated. Anstis also wrote a nice sequel to this 25 years later on picturing peripheral acuity.