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Robert J Zawadzki, Pengfei Zhang, Ratheesh Kumar Meleppat, SUMAN Kalyan MANNA, Edward N Pugh; Light induced water movement in the outer retina investigated by Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1294.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the hypothesis that water movement between the choroid sub-retinal space (SRS) and rods underlie light-activated rod outer segment elongation and that water movement through Bruch’s membrane manifest as a change in its refractive index.
Dark-adapted albino (Balb/c) mice were imaged in vivo with a custom SLO/OCT mice retinal imaging system. SLO delivered monochromatic light to trigger the opto-physiological signals , while OCT was used to probe the retinal response. OCT data were aligned to Bruch’s membrane, and further averaged to extract depth scattering profiles (average A-scans). Time-dependent changes of the depth scattering profiles were extracted and quantified by fitting Gaussian profiles to the hyper-reflecting bands of the outer retina.
Average data from 11 Balb/c mouse retinas exposed to an SLO scan (488 nm) that bleached 10% of the rhodopsin are shown in Fig. 1. The depth scattering profiles extracted from the OCT data reveal correlations between depth positions, intensity and FWHM of different outer retina bands. Specifically, initial changes in the BrM scattering intensity correlate negatively with BrM thickness and match the initial expansion of the ROS length (measured as ROS tips (ROST) position), suggesting water movement from the choroid to the SRS at the same time as water moves from the SRS into ROS to cause them to swell. Additionally, temporal correlation of increased scattering from the RPE apical site to the IS/OS and ROST scattering suggest that water activity in SRS increases at the same rate as in ROS. Small changes in ELM scattering intensity suggest only limited water transport between inner retina and outer retina during light activation of rods.
Correlations between depth positions, intensity and FWHM of different outer retina bands suggest that there is light-activated, osmotically driven water movement between different compartments of the outer retina into outer segments. The results also suggest much faster diffusion of water between the choroid and SRS as compared to SRS into ROS, and point to the choroid as a reservoir of highly mobile water available to respond to osmotic changes in photoreceptors produced by very strong activation of phototransduction . P. Zhang et al. PNAS 114.14 (2017): E2937
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Optophysiological signal extraction of hyper-reflecting bands in outer retina measured from averaged OCT A-scans
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