Difference in ocular damage by 40 and 95 GHz exposure to rabbit eye

Abstract

 

Purpose

 

Millimeter waves (MMW) are prevalent in high-speed wireless communication, automobile collision prevention systems and high-resolution radar imaging. We examined frequency (40 and 95 GHz) dependent differences of corneal damage in rabbit eye.

 

Methods

 

Pigmented rabbits (N=48, Dutch, 13-16 week-old) were exposed unilaterally to 95 GHz MMW at 200 mW/cm² for 6 or 10 minutes, and 40 GHz MMW at 200, 300, 400 mW/cm² for 6 min by lens antenna. Systemic anesthesia during exposure and ocular examination was induced by medetomidine hydrochloride (0.5 mg/kg). Ocular changes were evaluated by slit-lamp. Corneal surface temperature during exposure was recorded by thermograph camera (R300, NEC Avio). Microencapsulated thermochromic liquid crystal (MTLC) injected into the anterior chamber prior to exposure with color change recorded by video camera during exposure revealed heat transport.

 

Results

 

Corneal surface temperature following 95 GHz 200 mW/cm² , 6 and 10 min exposure was 42.6±2.1 degrees Celsius (C) and 43.2±1.3 degrees C, respectively (NS). Representative ocular damage were diffuse corneal epithelial cell damage immediately after exposure, corneal epithelial defect and corneal edema 1 day after exposure. Exposure for 10 min caused more severe corneal epithelium defect (12/12 eyes) than for 6 min (4/7 eyes). Maximum corneal surface temperatures by 40 GHz at 200, 300 and 400 mW/cm² were 41.4±1.1, 42.5±1.1, and 45.5±2.1 degrees C, respectively. Exposure for 6 min to 40 GHz at 200 mW/cm² caused transient corneal diffuse damage (3/6 eyes) and at 300 mW/cm² diffuse corneal epithelial damage (6/6 eyes). Diffuse corneal epithelial cell damage occurred immediately following exposure at 400 mW/cm² (3/5 eyes), and corneal epithelial defect (2/4 eyes) and corneal edema (2/4) 1 day after. Morphological evaluation showed 95 GHz at 200 mW/cm² and 40 GHz at 400 mW/cm², for 6 min, caused similar damage. Corneal surface penetration depth of 40 and 95 GHz was 0.59 and 0.31 mm, respectively. MTLC analysis revealed that 40 GHz exposure transported heat to iris and lens by aqueous humor convection within 20 sec, compared to 60 sec by 95 GHz (Fig).

 

Conclusions

 

Ocular heat effects by 40 and 95 GHz MMW differed with 95 GHz being more severe. MMW penetration depth, heat transport, and dissipation from cornea play important roles in ocular damage.

 

 

Aqueous humor convection by 40 or 95 GHz exposure

 

Keywords: 670 radiation damage: light/UV • 482 cornea: epithelium • 421 anterior segment