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Xiaofeng Tao, Jasdeep Sabharwal, Samuel M Wu, Benjamin J Frankfort; Chronic, mild intraocular pressure elevation impacts contrast sensitivity of retinal ganglion cells in mice. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5856.
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© ARVO (1962-2015); The Authors (2016-present)
Previously we have found that behaviorally measured contrast sensitivity in mice is significantly decreased after acute or chronic intraocular pressure (IOP) elevation, but this has not been studied in individual retinal ganglion cells (RGCs) from affected mouse retinas (van der Heijden, et al., 2016). Others have shown that the receptive field (RF) size of some RGC subtypes is reduced following the elevation of IOP to high levels (Della Santina, et al., 2013; Feng, et al., 2013). This study investigates both contrast sensitivity and RF size in mouse RGCs exposed to chronic, mild IOP elevation.
IOP elevation in wild-type C57BL/6J mice was induced by anterior chamber injection of polystyrene microbeads in one eye. Saline injection to one eye of additional animals was used as a control. 2 to 3 weeks following the injection, retinas were dissected, mounted on a 60 electrode multielectrode array (MEA), and action potentials recorded. To characterize the receptive fields (RFs) of RGCs, a series of 32x32 checkerboards (50x50 μm2 in size) randomly flickering between white and black at 15 Hz were presented to the retina (Cowan, et al., 2016). RF was determined by a model fit to the spike-triggered average (STA). Drifting bars were used to examine response to direction and contrast. Bars were randomly presented in 8 directions and at 18 contrast levels.
Microbead injected mice showed a mild but significant inter-ocular IOP difference compared to saline injected mice after 3 weeks (average IOP difference = 2.04±0.44 mmHg and 0.08±0.38 mmHg, respectively). RFs of 330 RGCs were identified and the average RF size in IOP elevated eyes did not differ significantly from those in control eyes. Bead injected eyes showed reduced firing rates at low contrasts (<10%), but no change in either contrast gain or response gain. Additional analysis regarding RF properties and an extended contrast analysis are forthcoming.
Mild IOP elevation via a microbead injection model did not cause changes in RF size, but did alter RGC contrast-dependent firing rate. These findings suggest that mild IOP increases have different effects on RGC function than more severe increases, and may preferentially impact contrast sensitivity.
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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