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^ Idebenone
^ Immune system Blood-born complex of cells and molecules which functions to react against foreign intrusion and initiate damage repair to the body.
^ Immunostaining Technique of histology to identify cell types based on immune reactions to cell components. Used extensively to identify and categorize eye nerve cell types.
^ Inflammation Immune system action on a tissue or organ. Usually a response to trauma, tumour, infection or immune system dysfunction. Classic gross signs are redness(rubor), heat (calor), pain (dolor), swelling (tumour). Naming convention uses "-itis" as a suffix. see Optic Neuritis and Arteritis. For a short review of causes of eye inflammation see:
Annabelle A. Okada, MD; John V. Forrester, MD. Ocular Inflammatory Disease in the New Millennium. Arch Ophthalmol. January 2000;118;116-119. PMID 10636424
^ Inhibition, Neuroreceptor Some neurotransmitters are inhibitory on their receptors. For example, GABA is inhibitory in the eye.
^ Inner Plexiform Layer Retinal layer where bipolar neurons synapse with retinal ganglion cells. Amacrine cells also interact at this level. Divided into outer and inner sublaminae. At the outer level sublamina a "Off" bipolars synapse with ganglion cells. While the inner sublamina b has "On" connections. See retinal layers.
^ Intima Inner lining layer of blood vessels. Endothelium plus supporting connective tissue and membrane.
^ Intraocular Pressure (IOP) Internal fluid pressure of eye. Measured with various tonometry devices. High IOP is associated with a higher risk of glaucoma. Lowering IOP with medication or surgery can to a large extent limit glaucomatous optic nerve disease. IOP also plays a role in Anterior Ischaemic Optic Neuropathy as optic nerve head (ONH) perfusion pressure equals mean blood pressure minus IOP. Raising IOP in people with vascular risk factors impinging on ONH blood flow may significantly effect ONH perfusion.
^ Intron Non coding regions in DNA or RNA. Also, intervening sequences. cf. Exon and Codon
^ Ions Atoms or groups of atoms which carry electric charge by virtue of loss or gain of one or more electrons compared to their proton count. Cations with positive charge ( + ) have lost electrons. Anions with negative charge ( - ) have gained electrons. Changes of concentration of ions in solution in cells are part of many electrical cell mechanisms including nerve impulses and neuroreceptor regulation. cf free radicals
^ Ionotropic Ligand-gated ion channel. A class of glutamate neuroreceptor with a multi subunit ion transport channel and extra cellular ligand site. i.e. a ligand-gated oligomeric ion channel. The class can be divided into NMDA and non-NMDA (AMPA-Kainate) groups. NMDA receptors are found in retinal ganglion cells and some amacrine cells. Non-NMDA receptors are on the post synaptic membrane of horizontal cells, OFF-bipolar cells, amacrine cells, and ganglion cells . cf Metabotropic.
^ Iridocorneal angle see Angle, iridocorneal
^ Iris The muscular pigmented ring regulating aperture size and sex appeal of eyes. It is part of the uvea which also includes the ciliary body and choroid. see IFOND logo
^ Isch(a)emia Lack of blood supply.
^ Isch(a)emic Optic Neuropathy Optic nerve disease due to lack of adequate blood supply. Classified into Posterior and Anterior Ischemic Optic Neuropathy, the latter is more common.
^ Isoniazid Anti tuberculosis drug known to cause optic nerve injury.
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