Optometry & Visual Performance 164 Volume 14 | Issue 2 | June 2026 Down for the Count “The problem is never how to get new, innovative thoughts into your mind, but how to get the old ones out.” –Dee Hock “Okay, Hugh,” Professor McIver began the session, “having established that visual acuity exams were arbitrarily developed based on an employment test for apprentice astronomers hundreds of years ago, are you ready to delve into logMAR thinking and expand your practice horizons?” “Actually, Professor McIver, I would like to hand this off to my classmate with the long name; we just call him Einstein as he seems to get things earlier than most of us. He is the one in our class who actually believes that this ‘logMAR’ thinking paradigm of yours might be promising.” Turning to the student nicknamed Einstein, Professor McIver quipped, “I am pleasantly surprised to hear that. Almost everyone who first hears of logMAR thinking initially has their eyes glaze over in flashbacks to high school math class, where logarithms initially confounded them before they slowly backed away to hide. Do please tell me why you think it has potential.” “Sure, it’s pretty simple really: I just hate memorizing formulas and heard that this logMAR thinking is just about counting steps without having to memorize much. That’s about it. I like things simple.” “You know, I don’t like memorizing formulae either,” Professor McIver said, smiling, “and the original Einstein is purported to have said not to memorize anything you could look up, and that is exactly what logMAR thinking is about: minimal memorizing and maximum impact. In fact, that is how the title of this little book came about! Low vision success with minimal memorizing; it’s so Einsteinian. “Now, if you can remember just a few simple principles and can count to ten, you too can be as successful with patients who have partial vision as you are with fully sighted patients. Let’s start counting.” “Reviewing ‘The Source’ quickly,” Professor McIver eagerly said, “we already know good sight has been arbitrarily though not unreasonably described as the ability to just recognize a letter that subtends a minimum angle of resolution of 1’ arc. Also, Weber showed us that human sensory ability to detect change is a log progression of 0.1 log steps. Putting those two principles together is what Ian Bailey and Jan Lovie-Kitchin did to create the first rational visual acuity chart, the Bailey-Lovie Chart. Let’s build one here to lock in those principles, and once we have that, we can proceed to unlock the power of logMAR thinking. I need another student to assist me. You, what is your name?” “Well sir, my name is Edward Neville, but people just call me E. N.” “Makes sense,” Professor McIver acknowledged. “If you are ‘down for the count’, we are going to begin at the beginning to build our logMAR chart; it really is a calculator just like slide rules of old in that one can do more complex math by just counting steps. Recalling that our starting point of good sight will be an MAR of 1’ arc, and its attendant VA of 20/20, what is the log of the MAR?” “Easy start,” exclaimed E. N., “High school math says that the log of 1 would be zero!” “Always good to start easy,” Professor McIver smiled. “Now, knowing what Weber discovered, what would be the next reasonable size letter as a JND larger than 20/20’s MAR of 1’ arc?” “Weber’s Law says that a 0.1 log increase in size would yield a JND, and that would mean that starting from 20/20’s logMAR of 0.0, we would add 0.1, which then equals 0.1 total. If we take the anti-log of 0.1, we get an MAR of ~1.25, and that yields a VA of 20/25,” E. N. said confidently. That fits perfectly with our vision charts for fully sighted patients, so no big deal, right?” “Perhaps,” countered Professor McIver, “it’s no big deal…yet. Let’s keep building our logMAR chart/ calculator. What is the next JND step, E. N.?” “Let’s do a bunch at once,” E. N. suggested. “We would climb the logMAR scale 0.1 steps at a time, so: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0. Taking their anti-logs gives us their MAR: 1.6, 2.0, 2.5, 3.2, 4.0, 5.0, 6.3, 8.0, and 10. We can translate the MAR into visual acuity by putting ‘20’ in the numerator and multiplying the MAR by 20, then inserting it into the denominator, like so: 20/32, 20/40, 20/50, 20/63, 20/80, 20/100, 20/125, 20/160 and 20/200.” “My name is Phoebe, and oh, my gosh!” she exclaimed. “I thought this logMAR thinking system was supposed to make low vision easier, and all I see is a lot of crisscrossing numbers that make my head spin.” “Hang on, Phoebe,” Professor McIver interjected, “we just have to get past this hump to show why logMAR is so powerful, then we can begin using the paradigm to make clinical measures easier. Let’s see if we can make a vertical table out of our numbers above to indicate how the logMAR chart/calculator can be used.”
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