Acta Ophthalmologica 2015
Correlation between corneal and ambient temperature with particular focus on polar conditions Jon Klokk Slettedal1,2 and Amund Ringvold1 1
University of Oslo, Oslo, Norway Department of Ophthalmology, Oslo University Hospital, Oslo, Norway
2
ABSTRACT. Purpose: To examine the relationship between human corneal and environmental temperature. Methods: An infrared camera was used to measure the corneal surface temperature in a group of healthy volunteers as well as in an experimental setting with donor corneas and an artificial anterior chamber, employing circulating saline at +37°C. Liquid nitrogen was used to obtain a very low temperature in the experimental setting. High ambient temperature measurements were performed in a sauna. Results: In healthy volunteers, the cornea required at least 20–30 min to adapt to change in ambient temperature. The relationship between corneal and external temperature was relatively linear. At the two extremes, +83°C and 40°C, the corneal temperature was +42°C and +25.1°C, respectively. In the experimental setting, corneal temperature was +24.3°C at air temperature 40°C. Conclusion: A rather stable aqueous humour temperature of +37°C and high thermal conductivity of the corneal tissue prevent corneal frostbite even at extremely low ambient temperatures. Key words: cornea – infrared camera – temperature – thermal conductivity
Acta Ophthalmol. 2015: 93: 422–426 ª 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd
doi: 10.1111/aos.12657
Introduction This study was triggered by the 100th anniversary of the famous race to the South Pole by Amundsen and Scott in December 1911 (Amundsen 1912; Scott’s Last Expedition 1913). Despite extreme and often treacherous conditions, both teams managed to reach the pole. Unfortunately, not all of them completed the return journey. With ambient temperatures down to 59°C, snowstorms, strong wind, and even some of the participants operating without any eye protection, cold-
422
induced corneal damage was never reported (Nordenski€ old 1880–1881; Nansen 1890, 1897; Amundsen 1907; Shackleton 1909; Peary 1910; Nobile 1929, 1931). Except for scurvy, visual problems are not reported in any of the diaries. On the other hand, frostbite of fingers, toes and facial parts are regularly mentioned. Indeed, this seems paradoxical because corium of the skin (1– 4 mm thick) is likely to minimize heat loss through its abundant capillary network, compared to the cornea, which is both thinner (0.5 mm thick) and avascular. Furthermore, there is a significant
correlation between corneal and finger temperatures for the indoor temperature range (Schwartz 1965; Girardin et al. 1999; Kessel et al. 2010), although these observations are apparently not valid for extremely low temperatures, as experienced by the polar pioneers. In modern society, ophthalmological emergency attendances are affected by the climate (Fejes et al. 2014), in which wind, humidity and temperature are important variables. In this connection, it is noteworthy that progress in ocular temperature measurements in general has recently been reviewed (Kocak et al. 1999; Geiser et al. 2004; Purslow & Wolffsohn 2005). However, few scientific reports of cold-induced blurred vision have so far been published (Freytag 1917; Wessely 1918; Ansari & Canning 2012), and these anecdotal cases indicate that low temperature was not the only possible cause for the pathological corneal response. On the other hand, a study on young crosscountry skiers competing at 16°C indicated transitory damage of the corneal epithelium, and the authors suggested that this was due to incomplete closure of the eyelids. Their study included 29 athletes of whom 26 had epithelial damage shown by punctuate red staining after instillation of Rose Bengal/fluorescein. The stain was only seen in the lower third of the cornea, with a fairly sharp convex border towards normal epithelium. Green staining was not seen. These superficial changes were completely healed within 24 hr (Kolstad & Opsahl 1969). In summary, the available literature, both
Acta Ophthalmologica 2015
diaries and scientific reports, leaves the impression that frostbite in the cornea does not occur, even in extremely low ambient temperatures. In the following study, this hypothesis will be evaluated by in vivo and in vitro experiments.
Materials and Methods An infrared thermographic camera (FLIR T 335; Boston, MA) for measurements of superficial temperature was used throughout. The camera was calibrated for a temperature range of 40°C to +120°C. Thermal sensitivity is
Correlation between corneal and ambient temperature with particular focus on polar conditions Jon Klokk Slettedal1,2 and Amund Ringvold1 1
University of Oslo, Oslo, Norway Department of Ophthalmology, Oslo University Hospital, Oslo, Norway
2
ABSTRACT. Purpose: To examine the relationship between human corneal and environmental temperature. Methods: An infrared camera was used to measure the corneal surface temperature in a group of healthy volunteers as well as in an experimental setting with donor corneas and an artificial anterior chamber, employing circulating saline at +37°C. Liquid nitrogen was used to obtain a very low temperature in the experimental setting. High ambient temperature measurements were performed in a sauna. Results: In healthy volunteers, the cornea required at least 20–30 min to adapt to change in ambient temperature. The relationship between corneal and external temperature was relatively linear. At the two extremes, +83°C and 40°C, the corneal temperature was +42°C and +25.1°C, respectively. In the experimental setting, corneal temperature was +24.3°C at air temperature 40°C. Conclusion: A rather stable aqueous humour temperature of +37°C and high thermal conductivity of the corneal tissue prevent corneal frostbite even at extremely low ambient temperatures. Key words: cornea – infrared camera – temperature – thermal conductivity
Acta Ophthalmol. 2015: 93: 422–426 ª 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd
doi: 10.1111/aos.12657
Introduction This study was triggered by the 100th anniversary of the famous race to the South Pole by Amundsen and Scott in December 1911 (Amundsen 1912; Scott’s Last Expedition 1913). Despite extreme and often treacherous conditions, both teams managed to reach the pole. Unfortunately, not all of them completed the return journey. With ambient temperatures down to 59°C, snowstorms, strong wind, and even some of the participants operating without any eye protection, cold-
422
induced corneal damage was never reported (Nordenski€ old 1880–1881; Nansen 1890, 1897; Amundsen 1907; Shackleton 1909; Peary 1910; Nobile 1929, 1931). Except for scurvy, visual problems are not reported in any of the diaries. On the other hand, frostbite of fingers, toes and facial parts are regularly mentioned. Indeed, this seems paradoxical because corium of the skin (1– 4 mm thick) is likely to minimize heat loss through its abundant capillary network, compared to the cornea, which is both thinner (0.5 mm thick) and avascular. Furthermore, there is a significant
correlation between corneal and finger temperatures for the indoor temperature range (Schwartz 1965; Girardin et al. 1999; Kessel et al. 2010), although these observations are apparently not valid for extremely low temperatures, as experienced by the polar pioneers. In modern society, ophthalmological emergency attendances are affected by the climate (Fejes et al. 2014), in which wind, humidity and temperature are important variables. In this connection, it is noteworthy that progress in ocular temperature measurements in general has recently been reviewed (Kocak et al. 1999; Geiser et al. 2004; Purslow & Wolffsohn 2005). However, few scientific reports of cold-induced blurred vision have so far been published (Freytag 1917; Wessely 1918; Ansari & Canning 2012), and these anecdotal cases indicate that low temperature was not the only possible cause for the pathological corneal response. On the other hand, a study on young crosscountry skiers competing at 16°C indicated transitory damage of the corneal epithelium, and the authors suggested that this was due to incomplete closure of the eyelids. Their study included 29 athletes of whom 26 had epithelial damage shown by punctuate red staining after instillation of Rose Bengal/fluorescein. The stain was only seen in the lower third of the cornea, with a fairly sharp convex border towards normal epithelium. Green staining was not seen. These superficial changes were completely healed within 24 hr (Kolstad & Opsahl 1969). In summary, the available literature, both
Acta Ophthalmologica 2015
diaries and scientific reports, leaves the impression that frostbite in the cornea does not occur, even in extremely low ambient temperatures. In the following study, this hypothesis will be evaluated by in vivo and in vitro experiments.
Materials and Methods An infrared thermographic camera (FLIR T 335; Boston, MA) for measurements of superficial temperature was used throughout. The camera was calibrated for a temperature range of 40°C to +120°C. Thermal sensitivity is
