Optometry & Visual Performance 159 Volume 14 | Issue 2 | June 2026 Article • Clinical Guide to Einsteinian Low Vision Rehabilitation: Part 2 of 4 Bennett McAllister, OD • Western University of Health Sciences • Pomona, California The Longest Journey Begins with the First Step “The noblest distinction of man is his passion for knowledge.” –Will Durant “Professor McIver, we have a question for you,” said the spokesperson for the small cadre of low vision students at the office door. “May we come in?” “Certainly.” Replied Professor McIver. “What is on your mind?” “Well,” began the first student hesitatingly, “we have a conundrum. It seems to us that everything we have been taught so far regarding visual acuity (VA) is that 20/20 is perfect vision, and that 20/20 should be our goal for each patient, but that seems impossible for patients with low vision, and on top of that, we don’t even know where 20/20 came from.” “Well, first, 20/20 is not nor ever has been ‘perfect vision,’ and it is not even vision, it is sight. There is a difference between the two, with sight being the ability to distinguish angular subtense and vision being the brain’s cognitive gestalt. Definitions aside for now, however, I think the best way for you to gain a good understanding of ‘20/20’ is to dive deep into ‘The Source’. There is a very interesting story of how we came to 20/20 and what it really means. Let’s go meet Robert Hooke from history.”7 “Come in,” Robert Hooke said to the group of applicants. “As you should know from the notice I posted, I am looking for an assistant with good sight to help me with my studies of the star systems.” It was the late 17th century, and the nascent concept of experimental scientific method was rising. The Royal Society of London was home to a number of great Bennett McAllister, OD Pomona, California Associate Professor, Western University of Health Sciences, College of Optometry BA, Social Science, California State College, San Bernardino BS, Physiological Optics, 1979 OD, University of California, Berkeley, 1981 Fellow, AAO and Diplomate in the Low Vision Section scientists, including Robert Boyle and Isaac Newton in addition to Robert Hooke. It was clear and dark that night, unusual for London, as Robert Hooke took his apprentice applicants out to view the night sky. Taking them aside, one by one, he directed their attention to Ursa Major (Big Dipper) and asked them to count the constituent stars. “I am sure there are seven,” many of the hopefuls said one after another, only to hear, “Thank you, but you are not correct. You may go,” Robert Hooke disappointedly said, again and again. “I count eight,” one candidate finally announced, and he was hired on the spot. At last!” Hooke exclaimed, “I have found an assistant with good sight! I can always count on Alcor and Mizar to be arbiters of good sight, as the stars are static and will always be available to me in the future when I need new apprentices.” “What are Alcor and Mizar?” the student spokesperson chimed in, bringing the group back to the present. “Why, those are what look like a binary star in the handle of the Big Dipper,” Professor McIver said, stepping away from The Source. “You see, the angular separation, combined with the brightness differential between Alcor and Mizar, is 1’ of arc, or the minimum angle of resolution of a 20/20 letter. Just imagine for a moment how odd it is that our definition of good visual acuity goes back to an employment test from almost four centuries ago,” Professor McIver told his study group. “20/20 is nothing more than the essential angular subtense between the stars Alcor and Mizar in the Big Dipper used by Robert Hooke to qualify an apprentice for employment. But it marked an important point of departure by defining what good sight is and establishing a standard that could be replicated anywhere in the Northern Hemisphere.” “I don’t believe I have ever heard much of Robert Hooke,” another student exclaimed, “even though I was a science major as an undergraduate student.” “That is not surprising,” Professor McIver explained, “as Robert Hooke had a significant falling out with Isaac Newton, accusing Newton of plagiarizing his work. As you might imagine, that did not sit well with the powerful Newton, who, as head of the Royal Society, it has been suggested, canceled Hooke even to the point of having his portrait ‘disappeared’. Whether that story is true or just apocryphal, we now know that
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