Smartphone App May Be a Simple Tool to Measure Abnormal Eyeball Protrusion

A smartphone app could allow ophthalmologists to more easily measure abnormal eyeball protrusion due to Graves orbitopathy and other intraorbital conditions, according to a cross-sectional study.

Of 39 patients, the smartphone app showed relatively high accuracy and precision, interoperator reliability, and test-retest reliability for measuring exophthalmos compared with the historic standard and a high-resolution 3-dimensional scanner, reported Konrad P. Weber, MD, of the University of Zurich, and colleagues in JAMA Ophthalmology.

There were no significant differences between the three techniques among 23 patients and 16 healthy volunteers, with a mean difference in eyeball protrusion of 3.3 mm and 0.8 mm, respectively.

The smartphone app was convenient to use and didn’t require much skill, Weber and team noted, versus the traditionally used Hertel exophthalmometer, which was invented more than a century ago and “may be difficult to operate by an inexperienced examiner, prone to reading errors, and may have poor interoperator reliability and test-retest reliability in clinical practice.”

“The smartphone performed better than the Hertel for all three parameters,” Weber told MedPage Today. “We hope that we can replace the historic Hertel exophthalmometer with a smartphone app, which every ophthalmologist can carry in their pocket.”

The 3D scanner did the best job, Weber added, but it costs about $20,000, “performed only slightly better [than the other tools], and needed a lot of post-processing. The only better measurement methods may be CT and MRI scans of the head. But both methods are impractical to use in clinical practice, and CT scans need radiation.”

The researchers reported that accuracy and precision agreement between exophthalmos measures with the smartphone and the Hertel exophthalmometer showed an intraclass correlation coefficient (ICC) of 0.89 (95% CI 0.80-0.94) and 0.93 (95% CI 0.83-0.97) for the high-resolution scanner.

Interoperator agreement was highest for the high-resolution scanner (ICC 0.99, 95% CI 0.98-0.99), followed by the smartphone (ICC 0.95, 95% CI 0.92-0.97) and the Hertel exophthalmometer (ICC 0.91, 95% CI 0.85-0.95), while test-retest reliability was similarly high for the smartphone (ICC 0.93, 95% CI 0.82-0.95), the Hertel exophthalmometer (ICC 0.92, 95% CI 0.83-0.96), and the high-resolution scanner (ICC 0.95, 95% CI 0.89-0.97).

Kathleen Digre, MD, a neuro-ophthalmologist at the University of Utah in Salt Lake City, told MedPage Today that the smartphone app “fills a need for those of us who are at the clinic. You just take your picture, get your answer, and you wouldn’t have to do anything more.”

Digre said she was especially impressed that the study showed how a specific patient was tracked over time during treatment for proptosis. With an app, patients may even be able to measure their eyeballs at home and send the results to doctors for review, she added.

In another interview, Andrea Tooley, MD, of the Mayo Clinic in Rochester, Minnesota, noted that studies have shown a wide variation in measurements from different users of the Hertel exophthalmometer. The new study offers the prospect of standardizing measurements, she said. “Any automation in ophthalmometry is great.”

And, she added, an app might be especially useful outside the clinic where Hertel devices aren’t available.

In a 2021 study, Tooley and colleagues reported that they successfully used a smartphone ruler app to perform exophthalmometry by examining photos of patients. The results weren’t significantly different than those produced by Hertel exophthalmometry, they reported.

For this study, Weber and team recruited 39 participants from the University Hospital Zurich’s department of ophthalmology from June 2019 to January 2022. The patients were older compared with the healthy volunteers (median age 54 vs 32), and the majority of both groups were women.

Participants were twice examined by three different operators using the trio of techniques: the Hertel exophthalmometer, the Artec3D high-resolution face scanner, and the Bellus3D FaceApp using an iPhone 11.

For the smartphone approach, “the 3-D scan was exported in a geometry definition file (OBJ) and processed with self-developed MATLAB software version 2019b (MathWorks) to determine the exophthalmos in millimeters,” Weber and team explained.

They noted two limitations: the small size of the study and the fact that no app is yet available.

What’s next? Weber said that “the method is patented and we are working on an app for the iPhone. Unfortunately, the medical device regulations are difficult to tackle for an academic researcher, so it may take some time until we can bring out the app after some refinements.”

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