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K. Tsubota, S. Nakamura, M. Shibuya, H. Nakashima, R. Hisamura, N. Masuda, Y. Yabuno, Y. Saito, Y. Ogawa; New Mechanism of Dry Eye Syndrome in VDT Animal Model: Hypofunction of the Lacrimal Gland by the Suppression of Blink Through Visual Tasks. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5330.
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There has been no proposed mechanism that accounts for progressive worsening of dry eye in VDT users. We have hypothesized that tear production decreases in addition to the excess tear evaporation during VDT work.
Eight-week-old female Sprague-Dawley rats (Tokyo Laboratory Animal Science, N=18) were placed on a swing (VDT model) or in a room (control) with low humidity for 7.5 h/d between 9:00 am and 5:00 pm. Lacrimal function and morphology were evaluated after undergoing 10 days of the swing procedure. Ex vivo experiment was performed to measure protein release from isolated lacrimal gland (LG) with 10-3 M carbachol or without carbachol for 90 minutes. The M1/M3/M5 triple KO mice were also evaluated for the lacrimal function and morphology.
During the time the animal was on the swing, blink frequency was reduced to one-third of the non-swing riding levels, which is similar to the results that have been reported by VDT users. The persistent reduction of tear secretion was observed even when the rats were not on the swing, with or without pilocarpine stimulation. Histological examination of the LG demonstrated that the entire area of the LG was occupied by enlarged acini with expanded cytoplasm full of secretory vesicles (table). Since the muscarinic receptors are considered to be the source of the major stimulation, we developed a M1, M3 and M5 muscarinic acetylcholine receptor-knock-out mouse. Very similar changes, including the accumulation of secretory vesicles in acinar cells, were clearly observed.
Our study supports the concept that a proper number of blinks are required in order for healthy LG function to occur. It is our belief that the current study findings will pave the way for further research or discoveries including nutraceuticals or pharmacological treatment modalities that will lead to their use to restore LG function.
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