Smartphone Exophthalmometry Accurate in Measuring Abnormal Eyeball Protrusion

Konrad P. Weber, MD

Credit: University Hospital Zurich

New data supports the use of smartphone exophthalmometry to measure exophthalmos in patients experiencing abnormal eyeball protrusion due to Graves orbitopathy or other intraorbital conditions.¹

The cross-sectional examination of 23 patients and 16 healthy volunteers indicated the accuracy and precision, inter-operator reliability, and test-retest reliability of the smartphone system to measure exophthalmos, compared with a historic Hertel exophthalmometer or a high-resolution scanner.

“Our smartphone scanning method may be readily available with little experience or special training needed for the examiner and likely takes less than a minute to record a patient,” wrote the investigative team, led by Konrad P. Weber, MD, department of neurology and ophthalmology, University Hospital Zurich.

Measurements of exophthalmos are critical for the diagnosis and care of patients with Graves disease and other intraorbital conditions leading to protrusion of the eyeball. Graves orbitopathy, or thyroid eye disease, is the most common cause of exophthalmos in adults, particularly affecting female patients. Currently, the clinical standard for measuring eyeball protrusion is the Hertel exophthalmometer, invented more than 100 years ago and prone to reading errors and misuse.²

Weber and colleagues tested the accuracy and precision, interoperator reliability, and test-retest reliability of 3-D scanning methods in comparison to the Hertel exophthalmometer. Their goal was to invent and validate a simple application to measure exophthalmos using the 3-D scanning feature of a smartphone.

Participants, including those with exophthalmos and healthy volunteers, were recruited between June 2019 and January 2022 from the neuro-ophthalmology outpatient clinic at the investigators’ center.

Each participant was scanned twice by 3 different examiners using 3 different methods: a smartphone, high-resolution 3-D scanner, or Hertel exophthalmometer. This was repeated at an interval of 2 weeks or after an exophthalmos-changing treatment. The primary measure for the analysis was the difference in eyeball protrusion.

A total of 39 participants were included in the analysis. In this population, 23 patients (mean age, 54 years; 15 [65%] female) showed a mean difference in eyeball protrusion of 3.3 mm and 16 healthy volunteers (median age, 32 years; 11 [69%] female) showed a mean difference of 0.8 mm, without significant difference between the 3 examination methods.

Investigators observed a strong and similar correlation between the difference in eyeball protrusion for all 3 tests. The accuracy and precision agreement between the exophthalmos smartphone measure and the Hertel exophthalmometer had an intraclass coefficient (ICC) of 0.89 (95% CI, 0.80 – 0.94); for the smartphone compared to the high-resolution scanner, the ICC was 0.93 (95% CI, 0.83–0.97).

Further, the analysis identified the narrowest limit of agreement, marking the highest interoperator reliability, for the high-resolution scanner (ICC, 0.99 [95% CI, 0.98 - 0.99]). This was followed by smartphone measurements with a slightly wider limit of agreement (ICC, 0.95 [95% CI, 0.92 - 0.97]). The Hertel exophthalmometer showed the largest limit of agreement, marking the lowest interoperator reliability of all 3 methods (ICC, 0.91 [95% CI, 0.85 - 0.95]).

As all methods indicated similar limits of agreement, they also indicated similar test-retest reliability, according to investigators. The mean ICC of all 3 examiners was 0.95 (95% CI, 0.89 - 0.97) for the high-resolution scanner, 0.90 (95% CI, 0.82 - 0.97) for the smartphone, and 0.92 (95% CI, 0.83 - 0.96) for the Hertel exophthalmometer.

Weber and colleagues found, as expected, that the high-resolution scanner showed the best accuracy and precious, and higher interoperator and test-retest reliability. However, the team also noted it required the longest examination time, most patient cooperation, and was suspectable to the involuntary movement of the patient.

As a result, the smartphone scanning method could prove more convenient for clinical use, as it is widely available and requires little knowledge from the examiner.

“Hopefully, with further refinement, the application will be approved for distribution on smartphones for future use in clinical practice,” investigators wrote.

References

1. Popov T, Fierz FC, Bockisch CJ, Weber KP. Using Smartphone Exophthalmometry to Measure Eyeball Protrusion [published online ahead of print, 2023 Sep 21]. JAMA Ophthalmol. 2023;10.1001/jamaophthalmol.2023.4044.
2. MuschDC,FruehBR,LandisJR.The reliability of Hertel exophthalmometry: observer variation between physician and lay readers. Ophthalmology. 92(9):1177-1180. doi:10.1016/S0161-6420(85) 33880-0