Optometry & Visual Performance 161 Volume 14 | Issue 2 | June 2026 determined that the proportional change for humans to detect a change—a just noticeable difference, or JND, if you will—is when the stimulus changes by 0.1 log from a baseline. If we take Robert Hooke’s 1’ of arc subtense as standard good sight, we can quickly build a visual acuity chart, a rational vision chart, with steps between letter sizes of 0.1 log steps. Bailey and Lovie did exactly that in the late 1970s with the Bailey-Lovie chart, the first rationally designed vision chart that incorporated human abilities as the guiding principle. The ETDRS chart then slightly modified the BaileyLovie chart and became the standard way to measure visual acuity ever since. In actuality, when we think deeper about how these charts were developed with logMAR principles, we find that they are calculating devices like a slide rule! Slide rules were the calculating devices that made possible the industrial revolution. They ruled the calculating world until the 1970s, when electronic devices took over. Therefore, using the slide rule properties of the logMAR, we can make accurate predictions of power, working distance, and telescopic power with nothing but a logMAR chart. But I am getting ahead of the progression of knowledge here; that is a lesson for another time. For now, it must be recognized that old charts and paradigms for measuring visual acuity only worked satisfactorily for fully sighted patients due to fortuitous circumstances, not scientific rigor. In order to properly take care of all of our patients, we need to break out of the old confines and embrace the power of logMAR thinking.” Hugh was quiet a moment, as was the whole class; then he said, “I for one cannot wait to see how to apply this, even though it seems a bit esoteric at this point.” “That is ‘fine’ for now,” Professor McIver smiled. “The following lessons will explain more and introduce techniques, processes, and methods to apply logMAR thinking. Class dismissed.” Rationalizing Near Visual Acuity “It ain’t what you know that gets you into trouble, it’s what you know for sure that just ain’t so.” –Mark Twain “I am glad we got this little study group together,” Professor McIver began. “You fourth-year students have had a decent amount of clinical experience by now and no doubt believe that you have a good grasp of visual acuity, what it means, and how to use it in patient exams. Distance VA (dVA) is pretty well standardized as being a Snellen fraction with numerator of object distance over a denominator of object size, always making sure we keep our units the same: i.e., metric vs. imperial. We commonly take that to be when tested at a distance of 20 feet, the patient can resolve a 20-foot letter: 20/20. Simple enough, and we all get that. We have already seen what that means in the most precise and psychometrically sound manner in an earlier lesson when we use non-standard test distances. As a related aside, it should be mentioned that “count fingers” is an abomination to psychometric integrity and should never be seen on a record as a form of visual acuity. Count fingers is an anachronism to be left for people who don’t know what visual acuity means. You see, there are drastically different sizes of fingers, from 120 foot letter to 200 foot letter, as many different color fingers as there are people, and different contrasting backgrounds such as dark scrubs or a white clinic coat. If you can’t get an acuity on the ETDRS chart at 2 meters, just grab a Feinbloom distance chart, and move closer to the patient. The Feinbloom chart goes all the way up to a 700 foot letter with high contrast and recognition numerals, so it is acceptable for very poor acuities. There is also the Berkeley Rudimentary Vision Chart for very reduced acuities. So, if I ever find you using “count fingers”, I will require you to turn in your psychometric integrity membership card. As you might surmise by now, “count fingers” is a trigger for your Professor McIver, so avoid using it at all costs. That being said, today, I want this group to focus on near VA (nVA) and apply the principles of dVA to nVA. You have each been working with near visual acuity for a while, and I want to hear your take on the various nomenclatures. We know there are four separate nomenclature terminologies in general use for recording near visual acuity, but we are interested in knowing what their differences are, their advantages and disadvantages, and which makes the most sense to use. Those four systems are: 1. Reduced Snellen (RS) 2. Point or ‘n’ units 3. Jaeger, aka J-System 4. M-Units “While you may have had classes, labs, or clinics together, I want to make sure you know each other. By way of introduction, we have today in our group Rochelle, Ahn, Jesse Johnson (J.J.), and Logan,”Professor McIver said. “Let’s begin with reduced Snellen.” “Oh,” exclaimed Rochelle, “let me take that. I find reduced Snellen so much easier than the other systems because it closely resembles distance Snellen, and I can know exactly what it means. The comfort level is great for me, and people outside our field can quickly
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