Articles techniques et présentations

Chronic dry eye disease can be effectively treated with red light, which has been shown to stimulate and unblock meibomian glands. Designing wearable low-level light therapy (LLLT) devices requires achieving an effective energy dosage while not overheating the surrounding tissue and inducing thermal damage. A model of a wearable mask consisting of an array of LEDs emitting at 640 nm was developed in COMSOL Multiphysics to quantify transient periocular tissue heating over the course of a 17-minute treatment. In addition to the mask, the model consisted of a full 3D head model with skull, eyeball with segmented anatomy, and eyelid with parametrically controlled thickness. The Geometric Optics interface was used to release rays from the LEDs according to manufacturer supplied angular distribution and power and the Radiation in Absorbing-Scattering Media interface computed light propagation into the tissue and the resulting spatially varying heat generation rate. The temporal evolution of tissue temperature including the effects of perfusion and heat transfer with the mask and surroundings was handled with the Bioheat Transfer interface. Additionally, temperature control was implemented using the Events interface and the IR temperature sensor used in the actual device was explicitly modeled to accurately capture the functioning of the control system. The depth of thermal penetration and peak temperatures of critical tissue such as the cornea were found over the expected range of operating parameters and tissue properties. Specifically, the offset of the LED array from the surface of the eyelid, the eyelid thickness, and the optical properties (absorption and scattering coefficients) were found to have a strong influence on tissue heating, displaying a difference of 4 – 5 oC over the range of values expected in clinical practice. The modeling approach provides a framework for evaluating design tradeoffs and defining safe operating envelopes prior to clinical testing.