A first-order model of thermal lensing of laser propagation in the eye and implications for laser safety

Abstract

Many medical studies have investigated the safety threshold of ocular media at various wavelengths. Understanding and determining the damage threshold of laser exposure to the retina is important in order to set safety guidelines. A phenomenon known as thermal lensing where a media’s index of refraction changes as the laser energy is absorbed causes the beam profile and subsequently the position of the focal point of the beam to change as the temperature changes within the media. These changes in ocular media such as vitreous and aqueous humor, the cornea, crystalline lens, and retina all result in a slight change in the beam profile making the prediction of the focal point and laser spot size at the retina difficult to accurately predict. This paper describes how the effects of thermal lensing in the eye can be investigated to aid in determining the damage threshold for pulse durations of a few nanoseconds and continuous wave, CW, laser irradiation delivered to the retina and the relationship of how the damage is related to multiple pulse exposures. We present a first-order modeling effort for the thermal lensing effect in the eye along with initial estimates of impact on damage thresholds as predicted through computational biophysics thermal damage models.Many medical studies have investigated the safety threshold of ocular media at various wavelengths. Understanding and determining the damage threshold of laser exposure to the retina is important in order to set safety guidelines. A phenomenon known as thermal lensing where a media’s index of refraction changes as the laser energy is absorbed causes the beam profile and subsequently the position of the focal point of the beam to change as the temperature changes within the media. These changes in ocular media such as vitreous and aqueous humor, the cornea, crystalline lens, and retina all result in a slight change in the beam profile making the prediction of the focal point and laser spot size at the retina difficult to accurately predict. This paper describes how the effects of thermal lensing in the eye can be investigated to aid in determining the damage threshold for pulse durations of a few nanoseconds and continuous wave, CW, laser irradiation delivered to the retina and the relationship of how the ...