Comparison of Light Sources for Potential to Induce Photic Retinal Injury

Abstract

Abstract: : Purpose: Iatrogenic retinal light damage has resulted from exposure to various instruments used to diagnose and treat ocular disease. The objective of this study was to assess the phototoxicity potential of fiber–optic endoilluminator light sources with different spectral compositions. Methods: Eyes of anesthetized Dutch Belted pigmented rabbits (N=5 rabbits per light source) were exposed for two hours to light (9.6 to 10.2 lumens) from a metal halide, tungsten halogen (Alcon Accurus) or Xenon light source with a bandpass (BP, 420–650 nm) filter (Alcon Accurus High Brightness Illuminator). The 20G fiber–optic endoilluminator tip was positioned 2–3 mm from the retina in a location ventral and nasal to the optic nerve head. Retinas were evaluated for morphologic lesions after a 48–hour recovery period. Results: Two–hour tungsten–halogen or Xenon (with BP filter) light exposures resulted in mild lesions consisting of ONL thinning, pyknosis of photoreceptor nuclei, and RPE melanin pigment clumping. Severe retinal lesions were observed in the outer and inner retina of all eyes after 2–hour exposure to the metal halide light source. Light microscopic examination of the lesions demonstrated obliteration of the ONL with remaining photoreceptor nuclei appearing pyknotic. In addition, pyknotic nuclei were found throughout the inner nuclear layer with damage to ganglion cells as well. Conclusions: Two–hour light exposure with the fiber–optic endoilluminator probe fixed in one location produced mild ONL lesions with the Alcon Accurus and Accurus High Brightness Illuminators. Similar exposure to the metal halide light source resulted in severe damage to all retinal layers. Short–wavelength filtration of the Xenon light source provided what appeared to be a brighter illumination of the retina with a good safety profile.

Keywords: radiation damage: light/UV • photoreceptors • apoptosis/cell death