Visual acuity apps aren’t even in the ballpark of comparability to in-person refractions, but new research that analyzed 24 currently available platforms suggests three that seem to perform the best if an office visit isn’t feasible.

“A growing number of ophthalmic health tool apps are available for both patients and clinicians, which may address the increasing demand for eye care in the future. As they are a relatively new form of technology, they are not without disadvantages,” the research team from the UK wrote in their paper.

Compared with traditional VA testing that relies on printed optotypes, smartphone apps suffer from a range of variables that can influence the accuracy of results. This includes screen size, aspect ratio, pixel density, contrast and screen brightness, the study noted.

With these limitations in mind, here are the three apps the authors said would be suitable for clinical practice:

Peek Acuity (Peek Vision): The standalone app measures VA using the tumbling E test and includes an interactive guide on proper usage. The app begins by measuring VA monocularly at a 2m distance. The optotype decreases in size as the patient correctly identifies its direction until the final VA is reached. If the patient is unable to identify the direction of the optotype at 2m, the user is prompted to decrease the test distance to 1m. If the patient fails to identify the optotype at 1m, the user is instructed to decrease the test distance to 30cm. The app offers two additional prompts corresponding to decrease VA, including a moving target, and ability to perceive the phone’s torchlight. Final VA is expressed as logMAR (0.0), and this can be switched to Snellen metric (6/6) or Snellen imperial (20/20). Peek Acuity has been clinically validated and shown to produce accurate and repeatable acuity measurement compared with conventional acuity charts in peer-reviewed research, the researchers noted.

Peek Acuity Pro (Peek Vision): The Pro version of the app is a CE-registered, class 1, medical device available in certain countries, and both versions (Peek Acuity and Peek Acuity Pro) are available for free on the Google Store. The two apps have methods for calibrating both optotype size and brightness. The limitation of these two apps is the inability for users to self-test since the test requires a second person to act as the device operator. In the context of ophthalmic telehealth consults, this would limit the suitability of the app to patients living with friends or family members who can accurately operate the device, the authors noted.

LooC–Mobile eye test (LooC GmbH): When testing near vision, the calibration stage involves using a mirror and the phone’s front facing camera to estimate the user’s interpupillary distance, which takes around 30 seconds to complete. The app uses a phone’s front facing camera and face-detection to determine the distance the device is being held from the face when measuring near VA, using the Ladolt C or tumbling E optotype. The testing process involves the user identifying the direction of the optotype of increasing or decreasing size depending on the user response. This is a test of monocular VA, and acuity is presented as a Snellen imperial.

This novel technique of calibration has not been employed by any of the other apps tested; however, there are some inherent limitations, investigators said. The method relies on detecting facial landmarking, which varies greatly depending on the optics of the camera being used, most notably the focal length. Additionally, the LooC–Mobile eye test hasn’t been clinically validated. Still, the app has been created according to the International Organization for Standardization standards for VA testing and has been implemented in individual ophthalmology clinics in Berlin with good results, the researchers said.

The investigative team started their study by conducting a systemic search for VA testing apps on the Google Play and Apple App stores. They narrowed it down to 16 apps (67%) that tested near vision, five (21%) that measured distance vision and three (13%) that offered both. Out of the 24 apps, only five (21%) offered a method of calibration of optotype size, while the three previously mentioned (13%) demonstrated evidence of clinical validation.

More work is needed in vision testing smartphone applications, including the clinical validation of individual apps, improved governance of health apps and cohort management systems for the integration of these programs into existing care pathways, the study suggested.