Being able to examine and measure a patient’s eyes remotely has taken on increasing importance, thanks to the current pandemic. For obvious reasons, this isn’t an easy task, even though some basic parts of an exam (examining the front of the eye, for example) can be done via telemedicine without too much difficulty. 

One type of remote testing that sounds plausible is visual acuity testing; yet getting patients to accomplish this with any level of accuracy at home has been a challenge. Many companies and software developers have created apps purportedly designed to do this for one basic reason: This measurement ties into the fairly common need to be measured for a new pair of spectacles. However, these apps don’t have to meet any legal or medical standards. The resulting plethora of options has been something resembling the Wild West.

Given the pandemic, however, ophthalmologists and optometrists have become interested in finding a medically useful way to effectively measure visual acuity at home. As a result, studies of the accuracy of different apps and other remote testing options have recently begun to appear in the literature. 

The technical challenges associated with visual acuity testing at home are not insurmountable. Some systems are showing merit in clinical testing.

According to one survey,¹ as of March 2020 at least 130 apps could be identified that related to eye-care functions, such as checking visual acuity, that could be considered relevant for ophthalmic practice but didn’t require special equipment (about half available on iPhone and half on Android phones.) Forty-one were intended for eye-care professionals. Only six of those were claimed (by the developers) to have validation. A 2021 survey of mobile apps purportedly designed to test visual acuity found that none of the apps examined by the study authors were, in their opinion, suitable for telemedicine use.²

Mohammad Rafieetary, OD, FAAO, who practices at the Charles Retina Institute in Germantown, Tennessee, sees home visual acuity measuring as a mixed bag. “Remote testing and home monitoring of medical parameters isn’t a new idea,” he notes. “For example, think about the history of the thermometer for detecting fever, or home monitoring devices for checking blood sugar levels. This phenomenon is just one way in which the field of eye care is expanding.”

Dr. Rafieetary notes, however, that some of the proliferating methods for “measuring your vision at home” may not be designed with the health of the user in mind. “A few of these apps are designed to help people who have vision issues realize that they need to see a doctor,” he says. “However, others are simply a way to bypass having a professional eye care provider re-examine your eyes when you need new prescription eyeglasses. They promote the idea of doing your refraction at home, picking your frame, measuring your pupillary distance and ordering your glasses without coming in to an office. They imply that you don’t need an eye doctor. The idea that you should only ‘see your eye doctor when you can’t see’ is a prescription for trouble—undetected glaucoma, undetected retinal disease and a long list of other problems.

“These tools, when clinically tested and applied appropriately, can be aids for overall health care,” he concludes. “But whether the majority of home vision-testing apps fall into that category is another question.”

An accurate, easy-to-use home visual acuity test would clearly be useful, not only during the current pandemic but in the future as remote medical care becomes more common. With that in mind, here are profiles of three current options for home visual acuity testing that have some clinical trial data supporting their validity as a medical tool.

• The Home Acuity Test. The Home Acuity Test, or HAT (available at homeacuitytest.org) is an open-source visual acuity screening test designed at Moorfields Eye Hospital in London that can be downloaded from the internet free of charge and printed out by patients. A silhouette of a credit card is included on the printout to help patients confirm that the size of the image is correct. Each downloaded eye chart is unique, to prevent memorization of correct responses. (The software is designed to produce billions of unique charts.)

The HAT chart consists of 18 randomly selected Sloan letters displayed over five lines. The letters on each line are half the size of those in the line above, with two letters on the top line and four on each line below. From a distance of 150 cm, the largest letters subtend 1.3 logMAR (3/60); the smallest letters subtend 0.1 logMAR (6/7.5).

Researchers at Moorfields tested the accuracy of the chart on 100 ophthalmology outpatients with a wide range of eye problems (two-thirds women, average age 55 years), and 50 control subjects, in May of 2020.³ All of the outpatient group reported subjectively stable vision. Patients were sent a 150-cm length of string to use to ensure the test was conducted at the correct distance from the chart. 

Two tests were conducted, using different charts, to confirm repeatability. The tests were conducted by the patient during a phone call with a clinician, who recorded the number of letters correctly read. Because of COVID-19-related restrictions, the measurements taken by the outpatients were compared to their most recent previous standard in-clinic exam rather than to a newly performed in-clinic test.

Among the outpatients testing themselves at home, the HAT results were one line worse, on average, than the previous in-clinic measurement. Among the control subjects, the measurements were, on average, between one and two lines worse than testing done with a standard clinic chart. The data showed that the test had high repeatability; between two consecutive tests, the mean difference in measured visual acuity was 0 letters.

The researchers concluded that the HAT could be a viable means of measuring visual acuity in patients unable to visit a clinic.

• The Peek (Portable Eye Examination Kit) Acuity app. This was developed by the International Centre for Eye Health in London; it tests distance visual acuity only. The test requires two people to complete, which could be a limitation for some patients who live alone. It’s free, but only available on Android devices. 

The Peek Acuity test measures visual acuity using the “tumbling E” format. It includes an interactive guide for users, explaining, among other things, how to calibrate the size and brightness of the optotypes. Scores are provided in Snellen units (metric, imperial or logMAR), but the app also creates a visual representation of the results that patients can readily understand. It’s been clinically shown to produce accurate and repeatable measurements of distance acuity, comparable to measurements obtained through standard testing. 

The developers tested the app on 233 elderly patients in private clinics and rural settings in Kenya, and found it to be accurate and repeatable in either situation.⁴ Other studies found the app to be valid as a tool for school screening,^5-8 when used by nonophthalmic staff in an emergency room,⁹ and when tested on Chinese and Australian individuals.¹⁰

Doctors can find more information about the Peek Acuity app at:  peekvision.org/assets/Documents/July2020_PeekAcuity_remote_healthcare.pdf.

• OdySight. OdySight is a clinically validated app for remote vision monitoring designed by Tilak Healthcare in France, where it’s available by prescription only. (The company recently signed an agreement with Novartis Pharmaceuticals to promote the app in the United States and around the world.) The name comes from the French word “odyssee”—“odyssey” in English. The app provides a mix of puzzles and vision tests (including an Amsler grid test) to encourage patient engagement.

 Once the app is accessed, it uses a proprietary algorithm to calculate the distance between the patient’s eye and the screen, as well as detecting the amount of ambient lighting. Distance to the eye is calculated using the patient’s interpupillary distance, the size of the camera feed and current frame, and the camera specs for the smartphone being used to conduct the test. A tutorial shows the patient how to do a test or puzzle.

The visual acuity test uses a tumbling E optotype; users indicates the orientation of the letter by sliding their finger in the same direction. Orientation and size of the letter changes after each response. If the patient doesn’t respond (indicating inability to determine the orientation) the app presents a “not sure” button the user can tap. The first time each eye is tested, a longer sequence of tests establishes a baseline visual acuity; follow-up tests are shorter. At the end of a test, the app displays the user’s score (for that test only).

A loss of five or more letters between visual acuity tests causes the app to prompt the patient to redo the test the following day. If the score is still the same (plus or minus two letters), both the patient and the doctor are notified of the change, and the user is asked to schedule a visit with the doctor. Test results automatically show up on the doctor’s dashboard. 

A clinical study was conducted by the company in conjunction with the University of Pittsburgh School of Medicine, and the Vision Institute and Quinze-Vingts National Eye Hospital, both located in Paris.¹¹ The study compared the test results to the gold standard tests for each variable tested (visual acuity, contrast sensitivity and Amsler grid). The data showed statistically significant agreement with gold-standard measurements of visual acuity in the majority of the test subjects.

^{1. Aruljyothi L, Janakiraman A, Malligarjun B, Babu BM. Smartphone applications in ophthalmology: A quantitative analysis. Indian J Ophthalmol 2021;69:548-53.}

^{2. Steren BJ, Young B, Chow J. Visual acuity testing for telehealth using mobile applications. JAMA Ophthalmol 2021;139:3:344-347.}

^{3. Crossland MD, Dekker trabecular meshwork, Hancox A, et al. Evaluation of a home-printable vision screening test for telemedicine. JAMA Ophthalmol 2021;139:3:271-277.}

^{4. Bastawrous A, Rono HK, Livingstone IA, Weiss HA, Jordan S, Kuper H. Development and validation of a smartphone-based visual acuity test (peek acuity) for clinical practice and community-based fieldwork. JAMA Ophthalmol 2015;133:930–7.}

^{5. Brady CJ, Eghrari AO, Labrique AB. Smartphone-based visual acuity measurement for screening and clinical assessment. JAMA 2015;314:2682–3.}

^{6. Dhanesha U, Polack S, Bastawrous A, Banks LM. Prevalence and causes of visual impairment among school children in Mekelle, Ethiopia. Cogent Med 2018;5:1554832.}

^{7. Zhao L, Stinnett SS, Prakalapakorn SG. Visual acuity assessment and vision screening using a novel smartphone application. J Pediatr 2019;213:203–10.}

^{8. Rono HK, Bastawrous A, Macleod D, Wanjala E, Di Tanna GL, Weiss HA, et al Smartphone-based screening for visual impairment in Kenyan school children: A cluster randomized controlled trial. Lancet Glob Health 2018;6:e924–32.}

^{9. Pathipati AS, Wood EH, Lam CK, Sáles CS, Moshfeghi DM. Visual acuity measured with a smartphone app is more accurate than Snellen testing by emergency department providers. Graefe’s Arch Clin Exp Ophthalmol 2016;254:1175–80.}

^{10. Han X, Scheetz J, Keel S, Liao C, Liu C, Jiang Y, et al Development and validation of a smartphone-based visual acuity test (vision at home). Transl Vis Sci Technol 2019;8:27.}

^{11. Brucker J, Bhatia V, Sahel JA, et al. Odysight: A mobile medical application designed for remote monitoring—a prospective study comparison with standard clinical eye tests. Ophthalmol Ther 2019;8:461-476.}