Natural protective mechanisms against endoscopic white-light injury in thefetal lamb eye

Objective: To evaluate light transmission, possible light trauma, and techn iques for protection of the fetal eyes during intrauterine videoendoscopic surgery in a sheep model. Methods: In vitro studies were done at various gestational ages, including spectrometry of light output by a halogen light source and telescope and li ght transmission by spectrophotometry in the range of 180-3000 nm through a mniotic fluid (AF) and fetal eyelids. In vivo electron-microscopic, morphol ogic analysis of the retinas of 65-, 95-, 108-, and 112-day-old fetal lambs with (n = 8) and without (n = 8) 30 minutes' light exposure to the open ey e was also done. Results: The light spectrum at the tip of the telescope was 400-750 nm, wit h a maximum irradiance of 3 x 10(-3) W/cm(2) at 580 nm. In the ultraviolet spectrum (less than 300 nm), irradiance was less than 0.5 x 10(-3) W/cm(2). Light transmission through ovine AF ranged from 30% at 300 nm to 89% at 70 0 nm at 84 days' gestation, decreasing to less than 0.01% (300 nm) and 70% (700 nm) at 112 days. Fetal eyelids did not transmit more than 1% of light (any wavelength). After direct in vivo light exposure, no retinal damage wa s found. Photoreceptors were present from 108 days onward, but chromophores were scant or absent at all ages studied. Conclusion: The light spectrum of a standard endoscope is limited to 400-75 0 nm; ultraviolet light is filtered out. The AF transmits harmful blue ligh t poorly. Fetal eyelids seem to protect the eye by extremely low transmissi on and light dispersion. Even with the eye open, no morphologic retinal dam age was found. The strong light sources used with fetal endoscopy did not a ppear to pose a threat to the fetal retina. (C) 1999 by The American Colleg e of Obstetricians and Gynecologists.