Optometry & Visual Performance 163 Volume 14 | Issue 2 | June 2026 critique of the Jaeger system, do any of your classmates wish to chime in?” “Yes, I would.” Ahn interjected. “Much like the point system, just because a test has been around a long time does not mean it is valid or reliable.” Rochelle then jumped in with, “And I do not see any working distance recorded when any J number is recorded, like J1 or J2, and so on.” “Excellent, both of you!” Professor McIver asserted. “In addition, J size is not standardized between chart manufacturers, and there is no accounting for letter readability or stroke height commonality for letters that go above or below the line of text, so even if one records the working distance of a J nVA, one is unable to record a Snellen fraction with an actual letter size because the size is not known. Therefore, the J-system is useless for someone interested in test task equivalence or psychometric integrity.” “But why do so many people use the J-system in practice then?” J.J. asked, exasperated. “For that answer,” Professor McIver replied, “one has to look at psychosocial reasons, not psychometric ones. Think back to when we discussed ‘The Source’. Recall the levels of confidence we have in each stage of evidence and the weight we assign to them. Also, recognize that the amount of material students and interns/residents must absorb inhibits them from drilling down to the foundation of each bit of new knowledge. Professors with stellar credentials and great respect for their work hold forth on the subjects of their expertise, and interns/residents memorize what they are told. Some of those interns/residents then go on to distinguished careers of their own and teach their students what they learned from their mentors, and so on, from generation to generation.” “But that is not the scientific method,” Rochelle interjected, stating the thoughts of each of the students in the group. “It is more like quackery, methodology where one does not test the claims of the proponent.”9 “Absolutely,” Professor McIver agreed. “Quackery is a methodology that places the burden of proof on the skeptic, not the proponent, which is the exact opposite of the scientific method. You see its use much too often in crazy theories on the internet, which subsume the naive with what sounds like science. But, in fairness to the busy intern or resident in health care, there is not always enough time in the moment to fully test all the pronouncements of the sages. Still, we need to take the time to think critically and test the common canons we use on a regular basis. Regarding the three ways we have looked at so far for measuring and recording nVA, specifically reduced Snellen, the point system, and Jaeger, we find that they are all incomplete and potentially misleading. Clearly, they do not meet the standards that our psychometric integrity demands, nor do they allow us confidence in test task equivalence.” “Logan, may I ask you to tell us about the fourth system of measuring and recording nVA with its advantages and disadvantages?” Professor McIver said, turning to the fourth student in the group. “Of course,” Logan replied. “I must say that I love the M-Unit system. It uses letters with an actual size. By definition, a 1 M letter subtends 5 minutes of arc at 1 meter. Since it is metric, we can set up a rational Snellen fraction with the test distance in meters over the M letter size. This allows us to compare nVA with dVA to see if the results make sense. Also, the letters have been chosen for equivalent readability, further enhancing our level of confidence in the results.” “That sounds like the M-Unit system is a slamdunk for becoming the standard for measuring and recording nVA,” Professor McIver stated, “but are there any drawbacks to the M-Unit system?” “None that I can see,” Logan smugly replied. “It is clearly the best psychometric system for measuring and recording nVA.” “Hold on,” J.J. cautioned after a thoughtful pause. “I learned today that psychometric advantage is not always what drives people, even the smartest ones. Psychosocial forces are powerful determinants of behavior and can at times override the scientific factors. While now I see that in a logical world, the standard for nVA would clearly be the M-Unit system, it is not used commonly in practice. Contemplating why it is not the worldwide standard leads me to believe that the inertia and habit of the psychosocial domain when using the other three nVA systems inhibits the widespread use of the most rational and soundest system in psychometric terms, M-Units.” “Well thought out and well stated, J.J.,” Professor McIver congratulated. “Therefore, in order to break fully from what we have established are the inadequate and misleading nVA systems of reduced Snellen, the point system, and Jaeger, going forward, we will henceforth always record nVA in a Snellen fraction, with the numerator being the actual test distance in meters and the denominator as the actual size of the smallest letter read in M-Units. Further along, we will learn how to use logMAR thinking to convert imperial measurements to metric and create Snellen fractions for reduced Snellen and point measurements, as long as they are recorded with test distance.”
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