human_reference_atlas part of Homo sapiens multi-tissue structure eye iris iris EV:0100345 BTO:0000653 Wikipedia:Iris_(anatomy) AAO:0010347 TAO:0001238 MESH:D007498 NCIT:C12737 uberon UMLS:C0022077 The eye of the adult lamprey is remarkably similar to our own, and it possesses numerous features (including the expression of opsin genes) that are very similar to those of the eyes of jawed vertebrates. The lamprey's camera-like eye has a lens, an iris and extra-ocular muscles (five of them, unlike the eyes of jawed vertebrates, which have six), although it lacks intra-ocular muscles. Its retina also has a structure very similar to that of the retinas of other vertebrates, with three nuclear layers comprised of the cell bodies of photoreceptors and bipolar, horizontal, amacrine and ganglion cells. The southern hemisphere lamprey, Geotria australis, possesses five morphological classes of retinal photoreceptor and five classes of opsin, each of which is closely related to the opsins of jawed vertebrates. Given these similarities, we reach the inescapable conclusion that the last common ancestor of jawless and jawed vertebrates already possessed an eye that was comparable to that of extant lampreys and gnathostomes. Accordingly, a vertebrate camera-like eye must have been present by the time that lampreys and gnathostomes diverged, around 500 Mya.[well established][VHOG] iridial anterior uvea The avian iris and ciliary body undergoes a transition from smooth-to-striated muscle during embryonic development [DOI:dx.doi.org/10.1006/dbio.1998.9019] AS ZFA:0001238 irises The adjustable membrane, composed of the stroma and pigmented epithelium, located just in front of the crystalline lens within the eye. SCTID:181164000 irides CALOHA:TS-0491 iris MA:0000273 EMAPA:19154 GAID:917 EFO:0004245 XAO:0000185 UBERON:0001769 The opaque muscular contractile diaphragm suspended in the aqueous humour in front of the lens of the eye. The organ is perforated by the pupil and continues peripherally with the ciliary body. [Dorian_AF, Elsevier's_encyclopaedic_dictionary_of_medicine, Part_B:_Anatomy_(1988)_Amsterdam_etc.:_Elsevier][VHOG] VHOG:0000101 FMA:58235