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“Infrared thermotopography shows promising results as a means of detecting eye diseases which induce or involve a change in the temperature of the anterior segment. It can easily detect and visualise even the smallest differences in the corneal surface temperature distribution,” Sven Beutelpacher MD told the German Society of Ophthalmology. In a study carried out at the Interdisciplinary Uveitis Centre of the Heidelberg University Eye Clinic, Dr Beutelspacher and his team used high-resolution and high-speed infrared thermography to study 28 patients with different types of anterior segment inflammation. The goal of this orientation study was to gain a first impression of “high resolution and high speed” thermography in the ocular region. The investigators used a VarioTHERM camera with a spectral range of 3.0 to 5.0 mm which uses focal plane array to make images. The picture frequency was 50 Hz and the temperature resolution around 30°C < 0.1 K (0.01 K mA). The camera has a PtSi-CMOS-Hybris detector which is cooled by a Stirling-cooler.
Ten otherwise healthy patients examined with this method constituted the control group. The left and right eyes of the patients were both photographed 50 times, each within 10 seconds. The images were taken at 50 cm from the corneal surface at an angle of 15°, with a 100 mm objective. The room was darkened and set at a temperature of 22°. The environment was air-conditioned with minimal air movement. The researchers asked the patients to close the eye they wanted to examine for 20 seconds before taking the images. They asked them not to blink in order to avoid discrepancies in the measurements. Altered readings due to eye movement or blinking were discarded. The temperature time course, temperature distribution pattern, minimal temperature, maximal temperature, standard deviation, and the differences between the measurements were all recorded. The investigators used Irbis Professional software (Infratec) to evaluate the readings. They took all the measurements along an axis running through both lid angles and through the central cornea. They also took measurements around a vertical axis that went through the corneal centre and throughout a circular field of the cornea. The investigators took the measurements two hours after giving eye drops and dressing the eyes. They did not apply vasoactive medications. The average corneal temperature of the control group was measured at 35.4 ± 0.1°C. All the control patients revealed a mean surface temperature decrease of 1.3°C in 10 seconds. The iridocyclitis patients revealed a "hot ring" in the area of the corneal rim above the ciliary body. The temperature difference between the central cornea and the sclero-corneal interface was widened (³T 1.8°C). In all, the corneal surface temperatures in these eyes were 2.2°C higher than in the control group. The investigators also measured a high temperature zone in patients with scleritis, due to the increased local circulation. The eye surface temperature in eyes with ophthalmic herpes zoster was no higher than in normal eyes. The dendrites, however, were more apparent due to the minimal temperature difference with the environment. The researchers noted a temperature difference of up to 3°C between eyes which had undergone cataract surgery and non-operated eyes. The increase in the surface temperature is related to eye trauma. Furthermore, a more rapid temperature decrease was observed in the area of the breaking tear film than in neighbouring corneal zones. Dr Beutelspacher explained that the pattern of the temperature distribution on the surface of the eye can offer important diagnostic clues, shown as early as 1966 by a French study group. Since then, clinicians seem to have repeatedly re-discovered the method to aid them in the diagnosis of tumour findings, inflammations of the anterior eye segment and periorbital region, and for tear physiology. Technological advances in the camera system and the use of either a Stirling motor or other methods of cooling the instruments, as well as the downsizing of parts, has both simplified the method and rendered more precise and reliable readings. Infrared thermotopography is an important differential diagnostic tool that has become a well-grounded method in other medical disciplines. It has been employed to control the by-pass circulation during cardiac surgery and is a means of investigating the differential diagnosis of peripheral vascular closure. Infrared thermotopography is implemented in dermatology and for breast cancer diagnostics. Its role in ophthalmology is still at the experimental phase, however. According to Dr Beutelspacher, this method can be useful in the differential diagnosis of eye tumours, as well as to document the temperature development during refractive laser surgery of the corneal surface in real time. Also, infrared phototopography can be used to detect an increase in corneal temperature during cataract surgery, which allows excellent visualisation due to the phaco energy, especially in non-pulse mode. Dr Beutelspacher stressed that these study results reflected only the first experiences made with infrared thermotopography and that the immediate relevance of the results was limited since standardising certain aspects of the method was not possible. “Although our study design examined the cooling down temperature of the corneal surface, we later realised that a standard cool down procedure using a precise quantity of water at a certain temperature and the use of a lid-opener to study the warming-up phase would have helped in creating standard conditions and a more reliable outcome,” he explained. Sven
Beutelspacher MD
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