First it was the penlight, then came along infrared cameras and now new iPhone-based test can measure pupillary light reflex (PLR). A recent study suggests it may offer greater portability and less expense than the high-tech infrared camera options with comparable results.

A team of Researchers compared the technical capabilities of their iPhone-based pupillometer, called the Sensitometer, with those of a laboratory-based infrared camera system. They measured pupil size— both dark-adapted steady-state pupil size and minimum pupil size after the flash—in 15 visually normal patients using the IR camera and the Sensitometer test.

The study found a statistically significant correlation between the IR and Sensitometer test measures for PLR and re-dilation size, and a mean difference of just 6% between the two methods. Investigators reported that 95% of subjects should have IR and Sensitometer test measurements that differ by 14% or less.

In contrast to previous smartphone-based pupillometry applications, the Sensitometer is software based, eliminating the need for external optics or light-emitting diodes, researchers said.

“There is excellent agreement between pupil responses recorded using the Sensitometer test and IR camera,” the investigators said in their paper, and noted the software’s potential to allow “simple, portable, inexpensive pupillary measurements.”

Still, the investigators suggested future work is needed to determine how the Sensitometer test performs in conditions where ambient illumination can’t be as carefully controlled. Additional studies could also be performed to compare pupil latency, they added.

McAnany JJ, Smith BM, Garland A, et al. iPhone-based pupillometry: a novel approach for assessing the pupillary light reflex. Optom Vis Sci. 2018 Oct;95(10):953-58.