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High speed airflow into the cornea accelerates evaporation and heat transfer. Eyelid blinking increases with increased airflow speed into the eye. Increased blinking increases corneal temperature when drops below normal level. In cold climatic condition high speed airflow causes rapid temperature drop. Most often, eye injuries caused by cold exposu...
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... We modeled the choroid together with the retina because both layers have blood flow and lie adjacent to each other and the choroid is relatively thin compared to the retina. The diameter of the eye along the pupillary axis (x-axis) is 25.10 mm and along the vertical axis (y-axis) is 23 mm [20]. The cornea is 0.5 mm thick in the center and thickens to 0.7 mm in the periphery. ...
... Similarly, when the epithelium is removed, the evaporation increases 20-fold [23]. The normal evaporation rate from tear-film is 40 Wm −2 [20]. In PRK, LASIK, or LASEK, the epithelium is removed, and hence, evaporation rate may increase 20-fold. ...
... The parameter values used in this study are blood temperature T b = 37 • C , evaporation rate E = 40W∕m 2 [20], ambient convection coefficient h cr = 14 W/m 2 °C [20], blood convection coefficient h b = 65 W/m 2 °C [20], blood density b = 1060Kg∕m 3 [20], blood specific heat c b = 3594J∕Kg • C [20], and emissivity of cornea = 0.975 [11]. The parameter values for different parts of the eye are presented in Table 1. ...
Refractive errors are the most common causes of vision impairment worldwide and laser refractive surgery is one of the most frequently performed ocular surgeries. Clinical studies have reported that approximately 10.5% of patients need an additional procedure after the surgery. The major complications of laser surgery are over/under correction and dry eye. An increase in temperature may be a cause for these complications. The purpose of this study was to estimate the increase in temperature during laser refractive surgery and its relationship with the complications observed for different surgical techniques. In this paper, a finite element model was applied to investigate the temperature distribution of the cornea when subjected to ArF excimer laser at a single spot using various beam delivery systems (broad beam, scanning slit, and flying spot). The Pennes bio-heat equation was used to predict the temperature values at different laser pulse energies and frequencies. The maximum temperature increase by ArF laser ([Formula: see text] frequency and [Formula: see text] pulse energy) at a single spot was [Formula: see text] for [Formula: see text] diopter correction ([Formula: see text] of ablation of corneal stroma) using broad beam, scanning slit, and flying spot beam delivery approaches respectively. The peak temperature due to a single pulse was estimated to be [Formula: see text]. Although the peak temperature (sufficient energy to break intermolecular bonds) exists for a very short time ([Formula: see text]) compared to the thermal relaxation time ([Formula: see text]), there is some thermal energy exchange between corneal tissues during a laser refractive surgery. Heating may cause collagen denaturation, collagen shrinkage, and more evaporation and hence proposed to be a risk factor for over/under correction and dry eye.
Localized hypothermia treatment can reduce the risk of vision loss due to ocular trauma. Hypothermia reduces inflammation and metabolic rate, and improves blood flow to prevent nerve and tissue damage. This paper presents a finite element thermal analysis to determine the efficacy of local hypothermia treatment administered using a scleral eye contact ring that acts as a heat sink. A realistic model of the human eye orbit, including fat and muscle, is created using MRI scans. A simplified CAD-based model is also created based on the first model. A transient analysis is performed by lowering the contact surface between the device and the eye to 4∘C. The study shows that the device lowers the temperature of the optic nerve head to a therapeutic range of 32 - 34∘C in less than 10 minutes of treatment, hence supporting the efficacy of such a device.
The human thermal comfort is affected by the bodys heat exchange mechanism conduction, con-vection, radiation, and evaporation. The mode of heat transfer between the body and environment depends upon the human internal physiological phenomena, together with the boundary conditions. The present paper provides the comprehensive overview of the thermoregulatory system of human body and studies the numerical solution of unsteady-state one dimensional Pennes bio-heat equation with appropriate boundary conditions. The solution is used to observe the temperature profiles at different thermal conductivities, and different heat transfer coefficients in the living tissue at the various time steps. Various physical and physiological factors across the cylindrical living tissue have been incorporated in the model.
