Three visual acuity tests taken at home produce results comparable to those achieved with standard tests taken in the office, researchers say.
All the tests are free. Two measure near vision, and the third measures distance vision.
“I think the purpose of these tests is for reassurance for patients and clinicians so we know that there is not a significant change,” Merina Thomas, MD, an assistant professor of ophthalmology at the Oregon Health and Science University (OHSU) in Portland, Oregon, told Medscape Medical News.
The study was published online March 31 in JAMA Ophthalmology.
Reliable home tests could allow more frequent monitoring of ocular conditions, provide safety from infectious diseases such as COVID-19, and reduce the need for travel. Ideally, they should be used to supplement rather than replace in-office tests, but ophthalmologists at OHSU considered relying on them for patients who didn’t want to come in for appointments during the pandemic, Thomas said.
“When COVID started within ophthalmology, no one really knew what to do about home visits and checking visual acuity, because we had heard of all of these apps and things, but no one had used them,” she added.
Paper charts, websites, and smartphone applications have become available for this purpose, but many have not been validated or require users to pay a fee. Some validation studies were conducted in research clinics under the supervision of clinicians, leaving Thomas and her colleagues to wonder how useful the tests would prove if patients were taking them on their own.
To help fill this gap, Thomas and her colleagues recruited adult patients from OHSU ophthalmology clinics between July 17, 2020, and March 9, 2021, whose visual acuity was 20/200 or better in at least one eye and who had access to an iOS (Apple iPhone) mobile device, a computer with internet access, or a physical address where they could receive a printed eye chart by mail.
The researchers randomly assigned 218 patients who had internet access or an iOS device to receive two of three tests:
University of Arizona/Banner Eye Health Chart, a distance vision test which uses an ETDRS chart that can be printed or viewed on a computer screen. It includes a picture of a quarter-sized circle for scaling.
Verana Vision Test Mobile Phone App, a near-vision test that is available as a free iOS application. This near-vision test comes with instructions to hold it at a “comfortable and consistent reading distance.” It displays a letter at a time and gives patients six options to select from regarding which letter they have seen.
Farsight.care website, a near-vision test that is available on a publicly accessible web page. It uses a number chart and a line to measure against a credit card for scaling.
Twenty-eight patients without internet access or iOS devices received the printed University of Arizona chart by mail.
The researchers asked the patients to complete their tests within 3 days of a standard evaluation in their clinic.
Of the 218 patients assigned to take two tests, 51.3% submitted results. Nine of the 28 who received tests by mail submitted their results. There was no significant difference in age, sex, clinic, ZIP code, or training time between those who completed the tests and those who didn’t.
“I think in general it was just that patients honestly forgot to do it,” Thomas said. “And it may be helpful, if this was used in clinic, to send a reminder.”
The mean in-office acuity for all the patients was 0.11 logMAR (slightly less than 20/25). The mean difference in visual acuity measured at home compared with the visual acuity measured in the office was -.07 logMAR with the printed chart. It was -.12 logMAR for the mobile phone app and -.13 logMAR for the website. All of these differences were within one line on an ETDRS chart, and the differences among them were not statistically significant.
The researchers measured the Pearson correlation coefficient, where -1 is a perfect negative correction, 0 is no correlation, and 1 is a perfect positive correlation. They found that the printed chart yielded a coefficient of 0.72; the mobile app, 0.58; and the website test, 0.64.
On a Bland Altman plot, the three at-home tests had similar upper limits of agreement, but the mobile phone app and the website test and greater lower limits of agreement than the printed chart.
To see how well the tests could measure changes in visual acuity over time, the researchers analyzed the subset of patients whose visual acuity changed by 0.2 logMAR or more (at least two lines) between baseline and follow-up clinic visits. They found that the positive predictive value ranged from 18.9% to 25.6%, while the negative predictive value ranged from 94.1% to 97.9%. There wasn’t a significant difference among the tests, but taken together, these results suggest that a test result showing a change in acuity may not be reliable and should be verified with a test in a clinic, Thomas said.
On a survey, the average participant said the tests were easy to view and understand. Asked about their confidence in the results and their willingness to continue using the tests, they gave neutral responses on average.
Although the differences among the tests were not statistically significant, the trend toward better results with a paper test is worth considering, said Michael Crossland, PhD, a senior research fellow and optometrist at Moorfields Eye Hospital in London, United Kingdom, who was not involved in the study.
“If you print something and paste it, you know exactly how big it is,” he told Medscape Medical News. Another advantage with a paper test is that it can be mailed to people who don’t have smartphones or internet access or don’t know how to use them, he added.
Overall, the study provided useful validation of the three at-home tests, though the large proportion of subjects who didn’t report any results was concerning, he said.
The study was supported by the National Institutes of Health and Research to Prevent Blindness. Thomas and Crossland have disclsoed no relevant financial interests.
JAMA Ophthalmol. Published online March 31, 2022. Full text
Laird Harrison writes about science, health, and culture. His work has appeared in magazines, newspapers, on public radio, and on websites. He is at work on a novel about alternate realities in physics. Harrison teaches writing at the Writers Grotto. Visit him at lairdharrison.com or follow him on Twitter: @LairdH.