sciences took place, from architecture to navigation to physics, chemistry, construction, and myriad other disciplines. A slide rule even went to the moon on the Apollo missions in the 1970s. Our logMAR charts are just like slide rules in that they allow quick and accurate calculations: in this case, knowing what a patient will see based on a single good measurement of visual acuity. I call it predictive analysis, and it is what gives logMAR thinking its clinical power.” “Sounds intriguing,” E. N. began hesitatingly, “but if it is so powerful and has been around since the 1970s, why isn’t it the standard of low vision care?” Pausing a bit before answering, Professor McIver said, “I too have wondered that, E.N., and it wasn’t until I applied the social thinking of punctuated equilibrium that an answer began coalescing in my mind. I think that logMAR processing was just too disruptive in that it required a substantial front loading to change paradigms before benefits would be visible, and people already in the field were satisfied with their own models while teaching them to their students. That is not to say that their ways were wrong or bad, but logMAR thinking allows more degrees of freedom, fewer assumptions, and makes formula-free practice possible. Whatever the reason for its non-dominant position today, I want to present to you predictive LogMAR MAR VA 0.0 1.0 20/20 0.1 1.25 20/25 0.2 1.6 20/32 0.3 2.0 20/40 0.4 2.5 20/50 0.5 3.2 20/63 0.6 4.0 20/80 0.7 5.0 20/100 0.8 6.3 20/125 0.9 8.0 20/160 1.0 10.0 20/200 1.1 12.5 20/250 1.2 16.0 20/320 1.3 20.0 20/400 Optometry & Visual Performance 166 Volume 14 | Issue 2 | June 2026 analysis and let you be the judge of its utility for when you are in practice. Let’s begin.” “There are only four parts to predictive analysis: 1. Measure and record VA with actual letter size and actual test distance, using consistent units. 2. Set a VA goal for improvement to meet the patient’s needs. 3. Count the steps on the logMAR chart between measured and goal. 4. Implement with working distance and dioptric power for near or telescope power for distance.” “Let’s look at the parts one at a time in sequence,” Professor McIver said. “First is measure and record VA. Sounds easy, right? But we have seen how inappropriate and sloppy measurements, and old but commonly used systems, can lead to psychometrically invalid results. In order to maximize the power of logMAR thinking properly, it is best to use M-Units for letter size and meters for test distance: actual letter size and actual test distance. Once we have a psychometrically valid visual acuity, we ask ourselves whether that is good enough for the patient’s needs. If the answer is no, then we need to set a goal for the letter size that will meet the patient’s needs. For our purposes here, we will be dealing with near point reading distances, though soon enough, we will see how the same principles can be applied to distance with telescopes. Always keep in mind that we are looking at JND steps on the logMAR charts.” “How about an example, Professor McIver?” Remi asked from the front of the room. “This sounds fascinating, but I don’t see how to apply it.” “Great prompt, Remi,” Professor McIver said. “Everyone get out their logMAR near point card and follow along. Ready? Okay, for part one of predictive analysis, let’s say a patient wants to read regular size printed material, which we have already established as 1 M, but can only read 1.6 M size letter at 40 cm with their current +2.50 D add. We record the acuity as 0.4 m/1.6 M. Now, part two: we ask with our inner voice, ‘Is that good enough?’ Since the patient has reduced visual acuity, the answer usually is of course not. For this example, let’s set our goal at 1.0 M print size since that is what the patient expressed as their reading need. Part three says that we count the JND steps between measured nVA and goal nVA, which in this case is two steps: 1.6 M the measured—>1.0 M the goal. Now comes the fun part of predictive analysis. Since we need two JNDs of improvement to get from the measured VA to the goal VA, we need two JNDs
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