Purpose: To compare horizontal white-to-white (WTW) corneal diameter measurements in children with the MultiMeasureTM iPhone application versus a caliper and evaluate the repeatability of MultiMeasureTM. Methods: This prospective, comparative pilot study enrolled 20 children. The horizontal WTW diameter was measured with calipers with the patient in primary gaze (caliper group). Subsequently, corneal photography was performed with the iPhone in primary gaze (primary group) and with a 20° head

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... rn (HT group). MultiMeasureTM was used to measure WTW. To evaluate repeatability of MultiMeasureTM, WTW was measured in 15 children from a clinic while awake (repeatability group) in primary gaze and with a 20° head turn. Three measurements were performed for all patients. Statistical significance was indicated by p<0.05. Results: The mean age of the sedated patients was 8.3 years (range, 2 to 15 years). The mean WTW was 11.68 ± 0.41 mm, 11.85 ± 0.28 mm and 11.34 ± 0.47 mm in the caliper, primary and HT groups respectively. There was a statistically significant difference between measurements in the caliper and HT groups only (p=0.006). Inter-test variability was not statistically significant different (p=0.45 primary group, p=0.37 HT group, p=0.37 caliper group). The mean age of 15 patients in the repeatability group was 7.6 years (range, 3 to 15 years). In the repeatability group, there was a statistically significant mean difference of 0.36 mm between the repeatability group in primary gaze versus head turned (p=0.001). Conclusion: The smart phone application was a fast, convenient, non-contact, repeatable method for measuring the corneal diameter in children in primary gaze.