The phone propped on a shelf, you a few steps away with one eye covered. Ever smaller letters appear on the screen, you answer aloud or with a finger, and after a couple of minutes the verdict arrives: so many tenths on the right, so many on the left. Convenient, immediate, available at eleven at night. But how far can you trust it?
Online eye tests and apps to measure eyesight have been studied for years, with interesting results and limits worth knowing. Here is what the validation studies have found.
In brief
- There are many eyesight apps, but few have been verified: in a 2020 survey only 6 eye-care apps out of 131 declared themselves validated1.
- In a meta-analysis, visual acuity apps identify most people with poor vision, with differences depending on age and on the tool3.
- On average the results come close to those of an examination, but for the individual they can differ by several lines; online glasses measurement is less accurate4,5.
- Many apps do not involve health professionals in their development and have no approval from regulatory authorities7.
- A visual acuity test does not look for eye diseases: it does not take the place of an examination9.
In this article
Online eye test and apps: what they measure
Most of these tools measure visual acuity, that is, the ability to tell small letters or symbols apart at a certain distance: the same thing that is measured with the chart hanging on the wall of the clinic. Some also try to estimate the refractive error to be corrected with glasses, others colour vision, contrast sensitivity or the distortion of lines.
The market is crowded. A 2020 analysis counted 131 eye-related apps: 32% were designed to measure visual acuity, and only 6, 4.5%, were declared validated by the developers themselves1. A 2024 review observes that the apps studied in the scientific literature are only a small part of those available2.
How far they agree with an examination
When they have been studied, many apps do well. According to the 2024 review, most of those evaluated reproduce traditional paper tests with good accuracy, also thanks to the uniform illumination of the screen and the possibility of changing the letters so that they are not memorised; some use the phone’s sensors to check distance and tilt2.
A 2022 systematic review with meta-analysis pooled 22 studies; six, with 24,284 participants, had enough data to calculate accuracy. Compared with the examination in the clinic, the apps identified about 86% of people with reduced vision between the ages of 6 and 22, and 85% of people aged 55 and over, with a specificity of 98% in this group3. Put another way: of 100 people over 55 with poor vision, the app flagged about 85 and missed about 15, with a wide margin of uncertainty3.
There is also a detail that is often forgotten. A review of 14 studies of tests done at home points out that even traditional charts do not always give the same result: between one measurement and the next, even in the clinic, there can be one or more lines of difference4. The same authors, however, start from an observation: there is no consensus on which technology measures eyesight at home in an accurate and repeatable way4.
The study
After cataract surgery, the check-up from the home computer
A randomised trial conducted in clinics in the Netherlands, Austria and Germany followed 94 people (188 eyes) who had had cataract surgery: some had their post-operative check-ups with a web test from home, the others with the traditional examination, and all had a safety examination after 4–6 weeks anyway. On average the online test measured visual acuity almost as well as the clinic chart, but for the individual the difference could reach about three lines. The estimate of the refractive error to be corrected was less accurate: with the correction suggested online people saw on average two lines worse than with the one measured by the examiner. Complications and patient-reported visual function were similar in the two groups5.
Why the results can be wrong
A test on a screen depends on details that are controlled in the clinic: distance, room light, the size and contrast of the letters. A review of 19 studies on eyesight apps noted that most did not describe the characteristics of the screens and stimuli used, and only two studies reported a calibration of the device; 73.7% were comparisons without a control group6.
The 2024 review concludes that, given the consequences of a wrong measurement, professionals must verify the validity of an app before using it in clinical practice2. A 2025 review lists the most frequent limitations: the absence of health professionals in development, the lack of approval by regulatory authorities and the poor possibility of sharing results with whoever follows you7. How to read a glasses prescription, finally, is explained in the article on dioptres and decimal acuity.
Monitoring macular degeneration from home
One field where home technology has more solid evidence is the monitoring of people with macular degeneration. The starting point is the Amsler grid, a sheet of squares that you look at to notice whether the lines become distorted. A meta-analysis of 10 studies with 1,890 eyes found that it identified the wet form of macular degeneration in 67% of cases compared with healthy eyes; the authors conclude that people at risk should have regular eye examinations regardless of the result on the grid9.
The study
The HOME study: a home device for macular degeneration
In a randomised trial, 1,520 people with a mean age of 72.5, at high risk of developing the wet form of macular degeneration, were assigned either to usual care or to usual care plus a home device that measured a central vision function every day and sent the data to a monitoring centre. After a mean of 1.4 years, those who used the device reached the diagnosis of the wet form having lost less vision: 4 letters against 9, as a median value. The trial was stopped early because efficacy had been shown10.
A 2023 review identified seven app-based eyesight tests designed for remote monitoring of macular diseases: four had obtained some form of regulatory authorisation, three were still in development, and further long-term, real-life studies are needed8. You will find the symptoms to know about in the article on macular degeneration.
Why they do not take the place of an examination
Even when an app measures visual acuity well, it measures only that: it does not look at the retina, the optic nerve or eye pressure, the elements on which the diagnosis of diseases such as glaucoma or diabetic retinopathy is based. Even a tool designed specifically for macular degeneration, such as the Amsler grid, has according to the authors of the meta-analysis a sensitivity that is not enough for reliable monitoring9. And the most solid studies used these tools alongside the examination, not in its place5,10. To find out how often to have a check-up, read the article on when to have an eye examination.
When to talk to an ophthalmologist
- If an online test or an app flags reduced vision: it is a reason to have an examination, not a diagnosis.
- If the test is fine but you notice symptoms, such as distorted lines, a patch in the centre or vision that is getting worse: the app’s result is not enough to rule out a problem9.
- Immediately: a sudden drop in vision, flashes of light or a shower of floaters. Call 112 or go to an emergency department (A&E); you will find the other warning signs on our page about eye emergencies.
Frequently asked questions
Are online eye tests reliable?
Some have been validated and, on average, give results close to an examination3,4. But for the individual they can be off by several lines, and many apps have never been verified in scientific studies1,5.
Can glasses be made from an online test?
The studies we have read urge caution: in a randomised trial the correction estimated online was less accurate than the one measured by the examiner, and with it people saw on average two lines worse5.
Can an app detect macular degeneration?
A home monitoring device gave good results in high-risk people already followed in clinical centres10, and several apps are being evaluated8. They are not, however, for making the diagnosis on your own.
If the online test is fine, can I do without an examination?
No. A visual acuity test does not look for diseases such as glaucoma or macular degeneration, and even for the Amsler grid, designed precisely for macular degeneration, the authors of a meta-analysis recommend regular examinations whatever the result9.
Online eye tests are a useful tool for noticing a change, and some have passed serious tests. But they are a thermometer, not a diagnosis: they say that something has changed, not why. For that you still need an examination.
Sources
- Aruljyothi L, Janakiraman A, Malligarjun B, Babu BM. Smartphone applications in ophthalmology: A quantitative analysis. Indian J Ophthalmol. 2021;69(3):548-553. doi:10.4103/ijo.IJO_1480_20 · PubMed 33595469 · PMC
- Bano T, Wolffsohn JS, Sheppard AL. Assessment of visual function using mobile Apps. Eye (Lond). 2024;38(12):2406-2414. doi:10.1038/s41433-024-03031-2 · PubMed 38509183 · PMC
- Suo L, Ke X, Zhang D, Qin X, Chen X, Hong Y, et al. Use of Mobile Apps for Visual Acuity Assessment: Systematic Review and Meta-analysis. JMIR Mhealth Uhealth. 2022;10(2):e26275. doi:10.2196/26275 · PubMed 35156935 · PMC
- Samanta A, Mauntana S, Barsi Z, Yarlagadda B, Nelson PC. Is your vision blurry? A systematic review of home-based visual acuity for telemedicine. J Telemed Telecare. 2023;29(2):81-90. doi:10.1177/1357633X20970398 · PubMed 33222600
- Claessens JLJ, Wanten JC, Bauer NJC, Nuijts RMMA, Vrijman V, Selek E, et al. Web-based telemonitoring of visual function and self-reported postoperative outcomes in cataract care: international multicenter randomized controlled trial. J Cataract Refract Surg. 2024;50(9):947-955. doi:10.1097/j.jcrs.0000000000001492 · PubMed 38809014 · PMC
- Mena-Guevara KJ, Piñero DP, de Fez D. Validation of Digital Applications for Evaluation of Visual Parameters: A Narrative Review. Vision (Basel). 2021;5(4). doi:10.3390/vision5040058 · PubMed 34842847 · PMC
- Goh C, Puah M, Toh ZH, Boon J, Boey D, Tay R, et al. Mobile Apps and Visual Function Assessment: A Comprehensive Review of the Latest Advancements. Ophthalmol Ther. 2025;14(1):23-39. doi:10.1007/s40123-024-01071-1 · PubMed 39576484 · PMC
- Balaskas K, Drawnel F, Khanani AM, Knox PC, Mavromaras G, Wang YZ. Home vision monitoring in patients with maculopathy: current and future options for digital technologies. Eye (Lond). 2023;37(15):3108-3120. doi:10.1038/s41433-023-02479-y · PubMed 36973405 · PMC
- Bjerager J, Schneider M, Potapenko I, van Dijk EHC, Faber C, Grauslund J, et al. Diagnostic Accuracy of the Amsler Grid Test for Detecting Neovascular Age-Related Macular Degeneration: A Systematic Review and Meta-analysis. JAMA Ophthalmol. 2023;141(4):315-323. doi:10.1001/jamaophthalmol.2022.6396 · PubMed 36795396 · PMC
- AREDS2-HOME Study Research Group, Chew EY, Clemons TE, Bressler SB, Elman MJ, Danis RP, et al. Randomized trial of a home monitoring system for early detection of choroidal neovascularization home monitoring of the Eye (HOME) study. Ophthalmology. 2014;121(2):535-44. doi:10.1016/j.ophtha.2013.10.027 · PubMed 24211172 · PMC
Study titles are given in their original language of publication. The superscript numbers in the text refer to these sources; citation details come from PubMed (National Library of Medicine).
