Infrared Cataract And Temperature Elevation Within The Eye. Tsutomu OKUNO

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1 Infrared Cataract And Temperature Elevation Within The Eye Tsutomu OKUNO International Commission on Non-Ionizing Radiation Protection National Institute of Occupational Safety and Health, Japan Tsutomu OKUNO

2 What is infrared cataract? IR cataract occurs in workers who have been engaged in the glass or steel industry for many years (e.g. glassblower's cataract). IR cataract is associated with exposure to intense IR emitted from molten materials and the inside of industrial furnaces. Recently, there is concern that infrared LEDs and diode lasers may cause cataract.

3 Interaction mechanism Photochemical mechanism ICNIRP 8 th INTERNATIONAL NIR WORKSHOP IR photon Chemical reaction Cataract Thermal mechanism IR energy Temperature elevation Chemical reaction Cataract

4 Temperature elevation within the eye Calculation based on a model of IR absorption and heat transfer within the eye Tsutomu Okuno (1991) Thermal effect of infra-red radiation on the eye: a study based on a model, Ann. Occup. Hyg. 35, Tsutomu Okuno (1994) Thermal effect of visible and infra-red radiation (i.r.-a, i.r.-b and i.r.-c) on the eye: A study of infra-red cataract based on a model, Ann. Occup. Hyg. 38,

5 Assumptions about IR absorption (1) IR absorption coefficient Optic axis

6 Assumptions about IR absorption (2) Monochromatic radiation Visible: 400 nm, 425 nm,, 775 nm IR-A: 800 nm, 825 nm,, 1400 nm IR-B: 1425 nm, 1450 nm,, 1900 nm Black-body radiation 1200 C: Working temperature of glass 1500 C: Melting point of iron Irradiance 0 Time

7 Assumptions about heat transfer Cornea: heat flux Inside: heat conduction Choroid: constant temperature The relative temperature elevations above normal, unexposed conditions within the eye were calculated.

8 Temperaure elevation ( C) Time course of temperature elevation λ = 600 nm Temperaure elevation ( C) λ = 1700 nm Time (min) Time (min) Anterior surface of cornea Anterior surface of lens Posterior surface of lens (100 mw/cm 2 )

9 Distribution of temperature elevation (1) Visible IR-A 1000 nm 100 mw/cm 2 10 min

10 Distribution of temperature elevation (2) IR-B IR-C Black-body radiation of 1200 C, 1500 C 1500 nm 100 mw/cm 2 10 min

11 100% ICNIRP 8 th INTERNATIONAL NIR WORKSHOP Transmittance of cornea and aqueous humor Visible, IR-A IR-B, IR-C Transmittance 80% 60% 40% 20% 0% Cornea Aqueous Cornea and aqueous CIE 203 :2012. A Computerized Approach to Transmission and Absorption Characteristics of the Human Eye Wavelength (nm)

12 Spectral distribution of black-body radiation Visible, IR-A IR-B, IR-C Spectral radiance (W/m 3 sr) 8E+10 6E+10 4E+10 2E+10 0E+00 84% 92% Wavelength (nm) 1500 C 1200 C

13 Mechanisms of temperature elevation Visible, IR-A IR-A, IR-B Goldmann Vogt Okuno Radiation Heat conduction

14 Maximum temperature elevation in the lens Temperature elevation ( C) Visible IR-A IR-B 100 mw/cm 2 10 min Wavelength (nm)

15 Summary on temperature elevation (1) The temperatures within the eye increase steeply with exposure for about 2 min, then level off and remain constant for exposures for more than about 5 min. For exposure to visible radiation and IR-A, the temperature elevation within the eye is the greatest at the iris. For exposure to IR-B and IR-C, the temperature elevation within the eye is the greatest at the center of the anterior surface of the cornea.

16 Summary on temperature elevation (2) For exposure to black-body radiation of 1200 C and 1500 C, the temperature elevation within the eye is the greatest at the center of the anterior surface of the cornea. Visible radiation and IR-B induce greater temperature elevations in the lens than IR-A, and are supposed to be more effective in causing cataract.

17 Summary on mechanisms For exposure to visible radiation and IR-A, the radiant energy is absorbed and converted into heat in the iris, which is then conducted to the lens. For exposure to IR-B and IR-C, the radiant energy is absorbed and converted into heat in the cornea, which is then conducted to the lens. For exposure to black-body radiation of 1200 C and 1500 C, the radiant energy is absorbed and converted into heat in the cornea, which is then conducted to the lens.

18 Cataract formation in rabbits exposed to IR-A Tsutomu OKUNO 1, Masami KOJIMA 2, Yoko YAMASHIRO 2, Sachiko YAMAGUCHI-SEKINO 1, Yoshihisa ISHIBA 3, David H. SLINEY 4 1 National Institute of Occupational Safety and Health, Japan 2 Kanazawa Medical University 3 Yamamoto Kogaku, Co., Ltd. 4 Johns Hopkins University Bloomberg School of Public Health

19 Exposure to 808 nm IR-A ICNIRP 8 th INTERNATIONAL NIR WORKSHOP

20 Results After one day of exposure at 6.1 W/cm 2 for 4 s

21 Threshold irradiance vs. exposure duration Thershold irradiance (W/cm 2 ) Exposure duration (s)

22 CIE technical report on infrared cataract Okuno, T. (Chair) Kojima, M. Schulmeister, K. Shang, Y.-M. Sliney, D. Söderberg, P. Stuck, B. Suzuki, Y. Tengroth, B. Japan Japan Austria Chinese Taipei USA Sweden USA Japan Sweden