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Bryan W. Jones, Phil Huie, Haimei Wang, Alexander Sher, Robert E. Marc, Daniel Palanker; Neural Activity in the Inner Retina After Photocoagulation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1170.
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Retinal photocoagulation is a common clinical intervention in many retinopathies. Though clinically effective, current laser therapies result in scotomas and scarring. We have demonstrated that during healing of small and light photocoagulation lesions, photoreceptors from adjacent areas migrate into the coagulated zone, restoring retinal continuity. This approach could allow for retinal laser therapy without the common detrimental size effects. Our goal was to assess the inner retina activity after photocoagulation with different levels of severity.
Laser exposures of "barely visible" and "moderate" grades were applied to rabbit retina (20ms, 200µm). 2 days and 2 months after photocoagulation the eyes were vitrectomized, retina was incubated for 30 minutes in vivo with 10mM 1-amino-4-guanidobutane (AGB) while exposed to flickering light, allowing AGB to permeate activated cation channels (iGluR, mGlurR6). The eyes were then aldehyde fixed in-situ, embedded in plastic, sectioned and processed for computational molecular phenotyping (CMP).
In the burns of moderate grade the two-month-old lesions were only partially filled with migrated photoreceptors, leaving scotomata. In the barely visible lesions, retinal pigment epithelium and photoreceptors were selectively ablated, but anatomic and metabolic signatures revealed robust bipolar, amacrine, horizontal and ganglion cell populations. These lesions filled in with photoreceptors after 2 months Signaling of the neural retina within these lesions, as revealed through AGB probing, was reduced 2 days after photocoagulation but was restored to normal levels after 2 months.
Optimizing the laser spot size, radiant exposure and pulse duration to target photoreceptors, while preserving inner retina allows the adjacent photoreceptors to shift and rewire to the local inner neurons. This procedure, while achieving its therapeutic goal of reducing metabolic load through reduction in the number of photoreceptors, may help avoid scarring, vision loss and other associated side effects of current photocoagulation protocols. Additionally, targeted coagulation of photoreceptors may represent an adjustable and reversible model of retinal degeneration and neural plasticity.
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