Retinal parallel processing

CME results from many ocular conditions but is not an independent disease entity. Retinal cell processes in Henle s layer run parallel to the surface of the internal limiting membrane, and the laxity of this layer fc>rms a potential reservoir for extravascular fluid resulting from breakdown of the blood-retinal barrier, which forms extracellular cystoid spaces in the perifoveal area. CME accompanies several retinal vascular diseases, including diabetic maculopathy central retinal venous occlusion, and branch venous occlusion. It may follow surgical procedures, most often cataract extraction and retinal detachment repair, or posterior inflammatory conditions, including pars planitis, chronic uveitis, and miscellaneous conditions such as retinitis pigmentosa. 

About half of rhodopsln s mass forms seven a-hellces, which are embedded In the lipid bllayer of rod disks. The remaining polypeptide chains extend Into the aqueous environment of the cytoplasm or the disk Interior, linking the helices. Retinal Is bound as a protonated Schiff base to a lysine amino acid residue In the carboxyl terminal helix. The chromophore is held In a pocket that is nearly parallel to the membrane surface. When light strikes rhodopsln, the 11-cis double bond of the protein-bound retinal Isomerlzes to the trans form, which leads to the separation from the protein opsin. To complete the visual cycle, the all-transretlnal slowly Isomerlzes back to the 11-cis Isomer, which recombines with opsin to reform rhodopsln. However, little Is known about how the Isomerization of retinal In rhodopsln triggers the transduction process (72,73) ... 

The polyene chromophore retinal or vitamin A aldehyde is the active molecule in the primary process of vision in almost all animals. Its ll-c form (Figure 12.13) easily inserts itself into a well-defined cavity in between seven parallel a helices in the protein opsin. With retinal present in this cavity, the protein is called rhodopsin. 

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