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Malcolm J Plunkett, John P M Wood, Glyn Chidlow; Slit-Lamp light triggers sustained IOP reduction in rats. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5327. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
In 1948, in the American Journal of Ophthalmology, Zaretskaya reported a reduction in intraocular pressure (IOP) in human subjects in response to photic stimuli. In the apparent absence of a plausible mechanism, this intriguing finding was adopted by fringe medicine and to our knowledge never received any further rigorous scientific study. In the current study, we attempted to replicate Zaretskaya's findings in rodents with a view to potentially proceeding to human studies.
Adult female Dark Agouti rats were maintained on a strict 12 hr dark / 12 hr light cycle for the duration of the study. Measurement of IOP occurred between 1 and 3 hours into the dark period, and was undertaken using a Tonolab tonometer. To prevent confounding movement during measurement, all rats were maintained at a level of very light anaesthesia with 1.4% isoflurane gas for a total duration of 40 minutes. Light treatment employed a Ziess style slit-lamp microscope along with a 5.4mm fundus laser lens; this applied a circle of white light of 2mm diameter to the central retina, at full intensity, for a period of 15 minutes per eye. To maximise pupillary dilation, 1% tropicamide was applied 10 minutes prior to light treatment. Animals were randomly divided into 3 groups of five (10 eyes each): control, untreated (C), tropicamide only (T), and tropicamide + slit-lamp light (T+L).
Measurements were carried out weekly and the IOP reduction of the T+L group was -15.4% at 2 weeks after the treatment, as compared to the control group. The change from baseline at 2 weeks was -1.5mmHg in the T+L group, and +0.7mmHg in the C group. The difference between the mean IOP values of these groups after 2 weeks , accounting for regression, was statistically significant (p = 0.002; ANCOVA). The effect lasted from approximately 1 to 4 weeks post treatment. Tropicamide only eyes showed no significant variation over the 4 week period.
This combination of tropicamide followed by slit-lamp light, but not tropicamide alone, is capable of a significant, prolonged IOP reduction in normal rats . This may be due to a disturbance of the pupillary eye reflex, and warrants further investigation.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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