Determinants of corneal temperature.

TLDR

Corneal surface temperature is governed by internal ocular tissues and the external environment, with blinking intermittently isolating the cornea from external influences; prior studies using contact and radiometric methods have examined temperature changes due to lid movement, ambient temperature, and inflammation, and this paper investigates the determinants of corneal temperature and inter‑eye temperature differences. The authors employed a bolometer—a balanced Wheatstone bridge with a radiation‑sensitive arm—to measure corneal temperature by detecting infrared emission; the device, calibrated from 4 to 26 °C, provides instantaneous readings within a 10 mm diameter area at a 0–5 cm distance, after a 15‑minute equilibration in a 18–26 °C room. Using this bolometer, the study obtained rapid, precise corneal temperature measurements, revealing that temperature variations can be detected between the right and left cornea of the same individual.

Abstract

THE surface temperature of the cornea is determined by adjacent ocular and extra-ocular tissues-an internal environment-and by conditions prevailing external to the body-an external environment.Any investigation of their effects is rendered more complex than would otherwise be the case in that the external environment is intermittently excluded during blinking so that, when the lids are closed, the thermal environment of the cornea is exclusively internal.The effect on corneal and pericorneal temperature of lid closure and opening (Braendstrup, 1952;Schwartz, 1964), environmental temperature (Schwartz, 1965), and inflammatory ocular disease (Huber, 1960) have been investigated previously.These authors measured temperature by contact; Zeiss (1930) also investigated the effects on corneal temperature of ocular inflammation but here a radiometric method was used.The purpose of this paper is to examine the various factors that determine corneal tem- perature and inter alia those that cause a difference in temperature between the right and left cornea of an individual. Material and MethodsThe instrument used for measuring corneal temperature is a bolometer (Fig. 1).This essentially consists of a balanced Wheatstone bridge, one radiation-sensitive arm of which is placed in the path of the spectrum emitted from the surface of which temperature is to be measured; this emitted radiation is "chopped" at 12-5 times a second and compared with that emitted by a built-in black- body radiator kept at a constant temperature.The radiation incident on the arm of the bridge produces a change in temperature and hence a change in resistance.The resulting change in current flow is amplified and recorded directly as a temperature reading on a dial (Fig. 2) which, at the calibration scale used, reads from 26 to 4°C. in units of 0.1 C. The bolometer is sensitive to infra-red radiation in the range of 1 to 25 p.The method of use is simple (Fig. 3).The bolometer is advanced to the surface whose tem- perature is to be measured and an almost instantaneous reading obtained on the dial.The distance between the bolometer and surface determines the extent of area of which the temperature is measured; with this particular instrument a separation of 0-5 cm.measures the temperature of an area having a diameter of 10 mm.In taking measurements the subject was allowed to equilibrate in a room in which the tem- perature-measured with an air thermistor probe (Fig. 4)-was kept between 18 and 26°C., ambient conditions which require no special equipment.In addition, draughts were excluded as far as possible and any direct artificial radiation source (sun-light, radiator, electric light) to the subject's face excluded.A 15-minute period of equilibration was chosen as a reasonable com-