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 ^ Radical, Free A highly reactive molecular species with one or more half filled valence orbitals i.e. unpaired electrons ( · ). In biochemistry these are often the products of the lipid peroxidation (auto-oxidation) chain reaction. The superoxide anion free radical, O2-· , produced by the reoxidization of reduced flavins by molecular oxygen, and nitric oxide (NO·), which has a complex role in the vasular and nervous system, are examples of free radicals. Free radicals can attack various cell molecular structures by oxidizing them (stealing their electrons) which could cause damaging effects to cells in some situations. Endogenous (produced by the body) and exogenous (nutritional) anti oxidant systems counteract free radical effects by limiting their production and by reacting with them (reducing them) in a non damaging way.


 ^ Recessive A mode of autosomal (not X or Y) chromosomal inheritance requiring the same form of the gene or the same mutation on both chromosomes in the pair for expression of the trait to happen. Therefore, both parents need to be carriers of the gene. The chance of both genes being passed are 1:4.


 ^ Reflex, Light Narrowing of pupil diameter in response to light stimulus. Retinal melanopsin system neural tracts carry the information from the retinal photoreceptor layer or from intrinsically photosensitive retinal ganglion cells to mid brain nuclei, especially the olivary nucleus, in the pretectal area. In Leber Hereditary Optic Neuropathy the pupil light reflex is spared. see Pupil reflexes

Wikipedia pupil reflexes

Wikipedia pupil light reflex

Wikipedia eye exam

Wikipedia opsins

Wikipedia intrinsically photosensitive retinal ganglion cells

Moura AL, Nagy BV, La Morgia C, Barboni P, Oliveira AG, Salomão SR, Berezovsky A, de Moraes-Filho MN, Chicani CF, Belfort R Jr, Carelli V, Sadun AA, Hood DC, Ventura DF. The pupil light reflex in Leber's hereditary optic neuropathy: evidence for preservation of melanopsin-expressing retinal ganglion cells. Invest Ophthalmol Vis Sci. 2013 Jul 2;54(7):4471-7. doi: 10.1167/iovs.12-11137. PMID: 23737476; PMCID: PMC4322722.

Georg B, Ghelli A, Giordano C, Ross-Cisneros FN, Sadun AA, Carelli V, Hannibal J, La Morgia C. Melanopsin-expressing retinal ganglion cells are resistant to cell injury, but not always. Mitochondrion. 2017 Sep;36:77-84. doi: 10.1016/j.mito.2017.04.003. Epub 2017 Apr 12. PMID: 28412540.

 ^ Refsum's disease Inherited metabolic disorder of the lipid alpha-oxidation pathway resulting in defective night vision, tremors and other neurologic abnormalities including optic neuropathy. An accumulation of phytanic acid occurs. Current treatment requires a diet free of chlorophyll, the precursor of phytanic acid.


 ^ Regeneration

Wikipedia nerve regeneration

Wikipedia Neuroregeneration

 ^ Relative Afferent Pupillary Defect Marcus Gunn pupil. Abnormal pupil reflex to light, implying a problem with the afferent pathway ie the optic nerve.

Wikipedia Marcus Gunn pupil


Wikipedia eye exam

 ^ Resting potential


 ^ Restriction fragment length polymorphism (RFLP) Technique of distinguishing characteristics of DNA. Used in conjunction with polymerase chain reaction for DNA mutation testing.


 ^ Retina Nerve layers of the eye limited on the inside by the transparent vitreous body and on the outside by Bruch's Membrane, the limit of the blood vessel rich choriod. At the central posterior pole is the fovea engulfed by the macula. This is the cone dominated area of central vision. The peripheral retina becomes more rod dominated and extends to the ora serrata where it meets the ciliary body anteriorly.

See the Webvision site for further retinal anatomic and physiologic details.


 ^ Retinal Layers The retinal nerve structure is based on three layers of nerve cells joined with two intervening layers of connections or neuropil. There is an outer pigment cell layer and an inner limiting membrane as well. Layers seen on light microscopy are described below from outer on top to inner below:

Retinal Layers on Microscopy - From outer (choroid-side) layers on top to inner (vitreous-side) layers on bottom. Note that detail varies from central fovea to peripheral ora serrata.

Pigment Cell Layer Pigment cells' basal lamina (part of Bruch's membrane), Pigment cells, microglia
Photoreceptor Layer Rod and cone photoreceptors, Muller cell apical villi, microglia
Outer Limiting Membrane Muller cell desmosome junctional complexes with rod and cone cell membranes
Outer Nuclear Layer Rod and cone nucleii, Muller cell processes, microglia, capillaries
Outer Plexiform LayerSynapses of rod and cone cell axons with bipolar dendrites and horizontal cells; Muller cell processes, microglia, capillaries
Inner Nuclear LayerBipolar cell bodies, Amacrine cell bodies, Horizontal cell bodies, Muller cell bodies, microglia, capillaries
Inner Plexiform LayerSynapses of Retinal ganglion cells dendrites with Bipolar cells axons and Amacrine cells; Muller cell processes, microglia, capillaries
Ganglion Cell LayerRetinal ganglion cell bodies, Muller cell processes, microglia, capillaries
Nerve Fiber Layer Retinal ganglion cell axons, Astrocytes, Muller cell processes, microglia, capillaries
Inner Limiting Membrane Merging Muller glial cell end feet processes with vitreous side mucopolysaccharide basement membrane

See: Helga Kolb. Simple anatomy of the retina. Webvision.

 ^ RNA, mRNA, rRNA, tRNA Ribonucleic acid


 ^ Rod A photoreceptor cell of the eye.


 ^ Rotenone Fish paralyzer from the roots of several plant species. Works by the inhibition of NADH-UQ reductase (Complex I).


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