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^ G-protein
^ GABA Gamma-Aminobutyric Acid. An amino acid neurotransmitter, largely inhibitory in the eye. ~a receptors, ~b receptors, ~c receptors.
See Webvision article for a discussion of GABA receptors in the eye.
^ Ganglion Cell, (Retinal) The retinal ganglion cells are neurons lining an inner layer of eye's retina which send their axons to the optic nerve. There are a variety of types. They use a variety of different neurotransmitter receptors to receive signals from other retinal cell layers, and are also adjacent to glia, supporting cells of the eye. It is retinal ganglion cells which are largely affected in optic nerve disease. The melanopsin containing retinal ganglion cell type are photoreceptors and are spared in some types of optic neuropathy.
Wikipedia Retinal ganglion cell
Wikipedia Intrinsically photosensitive retinal ganglion cells
Ganglion cell physiology. Ralph Nelson. Webvision.
Helga Kolb. Neurotransmitters in the retina.
^ Gene From www.genome.gov: The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein. Not to be confused with Allele
^ Genome The genetic make up of an organism. The DNA code that determines which proteins can be created by the cell. cf proteome
^ Genotype DNA code describing the potential traits of an organism rather than the actual traits expressed in an individual or phenotype.
^ Ginkgo Oriental tree whose extract has procirculatory and antioxidant properties. Ginkgo extracts are proposed for use in treating glaucoma.
Mozaffarieh M, Flammer J. A novel perspective on natural therapeutic approaches in glaucoma therapy. Expert Opin Emerg Drugs. 2007 May;12(2):195-8. PMID 17604496
^ Glaucoma A group of diseases of progressive optic nerve blindness usually beginning with peripheral vision loss of which the person is initially unaware. The process is usually, but not always, associated with elevated intraocular pressure.
Acute closed angle glaucoma is a rare medical emergency where the normal aqueous humor drainage pathway in the anterior chamber's scleral venous sinus (Canal of Schlemm) is blocked leading to a sudden rise in intraocular pressure, eye pain, vomiting and blindness. The syndrome can happen at any age including at birth.
More commonly chronic open angle glaucoma results in a slow vision deterioration initially imperceptible to the middle aged patient. There is evidence of multigene heredity. Americans of African extraction are at higher risk of chronic open angle glaucoma than their compatriots. Normotensive (normal pressure) glaucoma exists in all populations. Though it is more common in some population groups such as the Japanese.
Typical arcuate visual field defects correspond to superotemporal (upper outside) and inferotemporal (inner outside) damage in the optic nerve at the level of the lamina cribrosa.
Screening is the preferred method of diagnosis due to the otherwise late presentation. This presently involves regular checking of those at risk (ie those over forty years old, those with a family history of glaucoma or vascular disease and those with extreme short sightedness or "high myopia"). The methods are: testing for elevated intraocular pressure with various tonometry devices; looking at the back of the eye with an ophthalmoscope to assess retinal health and optic nerve head cupping; and visual field measurements with various perimetry devices. Devices used to measure the thickness of the retinal nerve fiber layer are being evaluated as screening and follow up tests.
Treatment currently is centered around lowering intraocular pressure with drugs and surgery, even in cases where pressure is not above average (normotensive glaucoma). Inspite of good compliance with treatment and effective lowering of intraocular pressure, vision tends to deteriorate although at a slower rate than non treated cases.
Much work is being done to discover other factors besides elevated intra ocular pressure which may be important in causing retinal ganglion cell loss in glaucoma. Knowledge of these other factors may result in improved treatments and may also be relevant to other causes of optic neuropathy.
Neville N Osoborne, John P M Wood, Glyn Chidlow, Ji-Hong Bae, Jose Melena, Mark S Nash. Perspective Ganglion cell death in glaucoma: what do we really know? Br J Ophthalmol 1999;83:980-986 ( August )
^ Glia Supporting cells of the nervous system. The proper functioning of these cells is vital to the health of the retina and optic nerve. In the eye there are three types of glial cells, Müller cells, astroglia and microglia. The optic nerve has astrocytes(astroglia), microglia and oligodendrocytes.
Müller cells predominate in the eye. They develop from the same progenitor cells as other retinal neurons. Their cell bodies sit in the retinal inner nuclear layer and their processes stretch to the inner and outer limiting membranes of the retina. See retinal layers. Their processes envelop all retinal neurons except at their synapses.
Astrocytes are brain derived support cells and are generally found only as far as the optic nerve and in the nerve fiber layer of the retina. Their peak numbers are at the optic nerve head. They are not found in the fovea or ora serrata. Because their processes envelope blood vessels of the optic nerve and nerve fiber layer they probably act as a blood brain barrier.
Microglia are of mesodermal origin rather than being true neuroglia. They probably developed with blood vessels. They are in every retinal layer.
Oligodendrocytes form myelin sheaths around optic nerve axons.
Yazdankhah M, Shang P, Ghosh S, et al. Role of glia in optic nerve [published online ahead of print, 2020 Aug 6]. Prog Retin Eye Res. 2020;100886. doi:10.1016/j.preteyeres.2020.100886 PMID: 32771538
See the Webvision site for further retinal anatomic details.
^ Glial cell line derived neurotrophic factor, GDNF
Jiang C, Moore MJ, Zhang X, Klassen H, Langer R, Young M. Intravitreal injections of GDNF-loaded biodegradable microspheres are neuroprotective in a rat model of glaucoma. Mol Vis. 2007 Sep 24;13:1783-92. PMID 17960131
^ Glioma, Optic
^ Glutamate
^ Glutamine
^ Glutathione
^ Glycine Amino acid acting as inhibitory neurotransmitter.
^ Gonioscope An optical device used to view the iridocorneal angle.
^ Growth factor (Neurotrophic factor)
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