Analysis of Heat Transportation to Crystalline Lens Surface by Aqueous Humor Convection

Abstract

Purpose: : To elucidate thermal transport in the anterior chamber by visualizing aqueous humor convection.

Methods: : Exp.1: Depth of penetration by 18 or 40 GHz radio frequency (RF) was calculated by measuring complex permittivity of ocular tissue (cornea, aqueous humor, lens, and vitreous). Exp. 2: Rabbit cornea, lens and vitreous temperatures before or during exposure to 18 or 40 GHz RF were measured by fluorescent thermometer.Exp. 3: Microencapsulated Thermochromic Liquid Crystal (MTLC) which changes color according to temperature was injected into the anterior chamber prior to exposure then images were recorded by video camera during 18 or 40 GHz RF exposure.

Results: : Exp. 1: Estimated ocular penetration depths of 18 and 40 GHz were 1.25 mm and 0.59 mm respectively. Exp. 2: The cornea and lens temperatures before exposure were 32.7±1.5°C and 37.4±1.0°C respectively (p<0.05). Temperature rises of 11.1°C(cornea), 3.8°C(crystalline lens), and 1.3°C(vitreous) were caused by 3 min exposure to 40 GHz of 200 mW/cm2. About twice incident power density was necessary under 18 GHz exposures to obtain similar temperature rises. Exp.3: Temperature rise in 18 GHz exposed eyes was first observed in the upper portion of the eye followed by the lower. Both upper and lower high temperature zones gradually moved into the central pupillary area. The thermal transport route in 40 GHz exposed eyes was observed to rise from the right under the cornea and the convection descended to the iris or the lens side.

Conclusions: : There is a possibility that the influence on the lens is different in each wavelength. Frequency response and convection of aqueous humor are involved in thermal transport in eyes suffering electromagnetic induced heat ocular damage.

Keywords: anterior chamber • aqueous • imaging/image analysis: non-clinical