Investigating the light emitting diode (LED) flashlight characteristics of a sample of smartphones for its safety in indirect retinal photography

Abstract

Introduction: the off-label use of smartphones for indirect retinal photography and videography made it a popular ophthalmic clinical practice for its ubiquity and simplicity which enhanced telemedical care. Smartphone indirect retinal photography involves focusing the bright flashlight from the light emitting diode (LED) source on the rear side of the phone on the patient´s retina. Phototoxic hazards of the bright light on the already compromised patients´ retina raise concerns that require safety studies. The aim of this work is to study the characteristics of LED flashlights of a sample of smartphone types currently in use by ophthalmologists in Egypt to evaluate for potential photobiological implications when used in conjunction with + 20-diopter indirect ophthalmoscopy condensing lens for indirect photography of the retina.

Methods: the spectral profile, weighted irradiance, and thermal exposure rates produced by a variety of smartphones´ LED flashlights currently used by ophthalmology specialists and trainees at the Comprehensive Outpatient Clinic of the Research Institute of Ophthalmology, Giza, Egypt, were tested in this study when collimated by a +20-diopter indirect ophthalmoscopy lens in a setup similar to actual indirect smartphone retinal photography.

Results: the spectrum of the LED flashlights of all tested smartphones fell entirely in the optically safe visible spectrum between 400-750 nm with no significant infrared or ultraviolet components. Two regions of main spectral distribution were noticed in all tested smartphones with a peak at 450 nm and the other ranging between 520 to 585 nm. Weighted irradiance was within the safe limits for ocular examination and ranged from 0.58 to 2.30 mW/cm² (safe limit is up to 706 mW/cm²) without a measurable thermal effect.

Conclusion: the LED flashlight of the tested smartphones appeared to be within safe limits when used for indirect smartphone retinal photography. However, the high composition of the short wavelength blue light spectrum may be a concern particularly with prolonged and repeated examinations.