Using Smartphone Exophthalmometry to Measure Eyeball Protrusion.

Abstract

The current clinical criterion standard for measuring abnormal eyeball protrusion is still the historic Hertel exophthalmometer, which is prone to reading errors. Therefore, a smartphone application has been developed to measure exophthalmos. To evaluate a relatively simple noninvasive measurement method for exophthalmos using a smartphone. This cross-sectional study compared smartphone exophthalmometry with the existing reference standard, the Hertel exophthalmometer, or a professional high-resolution 3-dimensional scanner. Participants were patients with exophthalmos due to Graves orbitopathy and other intraorbital conditions and healthy volunteers who were recruited between June 2019 and January 2022 from the Department of Ophthalmology, University Hospital Zurich. All participants were examined twice by 3 different operators using 3 different methods (smartphone, high-resolution scanner, or Hertel exophthalmometer) at an interval of a minimum of 2 weeks or after exophthalmos-changing treatment. Accuracy and precision, test-retest reliability, and interoperator reliability of eyeball protrusion measurements obtained with the smartphone compared to the Hertel exophthalmometer and the high-resolution face scanner. Of 39 participants, 23 patients (median [IQR] age, 54 [44-59] years; 15 [65%] female and 8 [35%] male) showed a mean difference in eyeball protrusion of 3.3 mm and 16 healthy volunteers (median [IQR] age, 32 [30-37] years; 11 [69%] female and 5 [31%] male) of 0.8 mm without any significant difference between the 3 methods. 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]). 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]). The findings of this study demonstrate relatively high accuracy and precision, interoperator reliability, and test-retest reliability for smartphone exophthalmometry. These data support the use of a smartphone in place of a Hertel exophthalmometer for measuring exophthalmos in the future.