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M.H. Geiser, M. Bonvin, O. Quibel, W. Balunga; Corneal and Retinal Temperatures under Various Ambient Conditions: A Model and Experimental Approach . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2446.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the distribution of temperatures between the cornea and retina under various external conditions, such as illumination and external temperatures, using a simplified heat exchange model. Methods: The human eye was modeled as a sphere filled with water and surrounded by a cylindrical homogenous heat source (water). Other heat sources included the choroid, the ciliary body, tear-film evaporation, metabolic activity of the extra-ocular muscles, diffuse retinal illumination and convection from ambient air. Retinal illumination was generated by having the eye look at a white surface illuminated by the sun (1000 W/m2). The corneal and retinal temperatures were derived from this model using finite element theory of heat transport. Each of five subjects (28±10 yr.) was placed in three different environments: –20°C, 20°C and 40°C. After 15 min, their corneal temperature was measured non-invasively with an infrared camera (Avio, wavelength: 3-5µm). Corneal temperatures were compared with the values obtained from the model, assuming no change in blood flow in the various eye tissues when changing the environment. Results: 1) The ciliary body and choroid contribute at least 20 times more than the retina to the retinal temperature; 2) the temperature increase of the retina due to solar illumination and metabolic activity is negligible; 3) a 10% reduction of choroidal blood flow induces a corneal temperature decrease of 0.2°C at -20°C and < 0.1°C at 20°C and 40°C. At normal choroidal and ciliary blood flows, changes in ambient temperature has a negligible effect on retinal temperature. Measured corneal temperatures agreed well with the values from the model: 26.4 ± 0.9 versus 26.8°C, at –20°C; 32.7 ± 0.3 versus 33.4 at 20°C and 36.2 ± 0.5 versus 36.7 at 40°C. Conclusions: Our simplified eye model predicts satisfactorily measured corneal temperatures under very different conditions. It also confirms the need for high choroidal and ciliary blood flows to maintain a constant retinal temperature.
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