SHORT-WAVELENGTH LIGHT REDUCES CIRCADIAN ELEVATION OF INTRAOCULAR-PRESSURE IN RABBITS

In light-dark entrained rabbits, the intraocular pressure (IOP) increa ses around the onset of dark due to the increased activities of ocular sympathetic nerves. This circadian elevation of IOP can be eliminated by exposing the rabbits to constant white light in the early subjecti ve dark phase. The spectral effectiveness of light causing the reducti on in IOP was studied using lights selectively filtered through variou s optic filters. Light which passed through a long-pass filter, with a cut-on wavelength at 570 nm or 530 nm, caused no change of the circad ian IOP elevation. A significant reduction of the IOP elevation was ob served with filtered light via the 495 nm long-pass filter and, to a l arger extent, with light via the 475 nm long-pass filter. Short-wavele ngth light (380-480 nm, peak at 432 nm) passed through a band-pass fil ter completely eliminated the circadian IOP elevation. The aqueous hum or concentration of norepinephrine (NE) under the short-wavelength lig ht was significantly lower than the NE concentration under the filtere d light via the 530 nm long-pass filter. Sensation of the short-wavele ngth light plays an important role in synchronizing the circadian elev ation of IOP in rabbits.