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Background: Heat exchange characteristics include not only temperatures and temperature distribution, but also heat flux (HF). Purpose: To examine temperature of and density of HF from the ocular surface in the eyes of patients with diabetic retinopathy (DR). Material and Methods: Sixty-two patients (123 eyes) with DR were under observation. Of these, 28 (55 eyes) and 34 (68 eyes) were diagnosed with non-proliferative DR (NPDR) and proliferative DR (PDR), respectively. They underwent a general clinical examination and measurements of temperature of the external corneal surface and density of HF from the eye. In addition, all NPDR patients underwent rheoophthalmography (ROG). Results: There was a significant difference in density of HF from the ocular surface (7.3 ± 2.1 mW/cm2 vs 6.3 ± 1.6 mW/cm2; p = 0.002), but not in ocular surface temperature (34.7 ± 1.3 °С vs 34.8 ± 1.1 °С; p = 0.8) between NPDR patients and PDR patients. HF density from the eye was positively correlated with the ocular blood volume coefficient (RQ; also named the rheographic coefficient) as assessed by ROG (r = 0.5; p = 0.01) for patients with NPDR. There was a relationship between the density of heat flux from the ocular surface and age of DR patients. Conclusion: Preliminary results suggest that (1) compared to the temperature of the ocular surface, the heat flux from the ocular surface better reflects the status of heat exchange in the eye, and (2) the technique might be promising as a diagnostic test for various pathological conditions involving impaired heat processes in the eye.

Background: Assessment of heat exchange processes in the human body is based on temperature and heat flux measurements. Today, there is no instrument for measuring the heat flux density from the eye. Purpose: To investigate the heat flux density from the ocular surface in healthy individuals using the developed thermoelectric device. Materials and Methods: The thermoelectric device for the measurement of heat flux from the eye has been developed within the framework of the partnership agreement between the Institute of Thermoelectricity and the Filatov Institute. Thirty-two healthy individuals (64 eyes) were under observation. Participants were divided into three age groups. They underwent a bilateral eye examination which included measurements of intraocular pressure, temperature of the external corneal surface, and heat flux density from the eye. Results: Mean room temperature during examination sessions was 21.3 ± 0.8 °С. In addition, mean temperature of the external ocular surface and mean heat flux density from the human eye were 34.6 ± 0.7°С and 7.7 ± 1.3 mW/cm2, respectively. We found that the heat flux density from the eye decreased with age in healthy subjects. Conclusion: The first ever thermoelectric device for real-time measuring of the heat flux density from the human eye was developed. The developed device was used to measure the heat flux density from the eye in healthy subjects, and to demonstrate the relationships of this characteristic with the temperature of the external ocular surface and subject age.