Eye Anatomy

Abstract

Eyes are like windows to the outside world, but their intricacies and functionalities are far more extensive than those of any given glass window. They are able to capture, adjust, and transform light into a chemical code that only the brain can decipher. Each structure of the eye works in accord with the next – refracting, constricting, dilating and chemically reacting to convert patterns of light. This article uses the mammalian eye as a primary model and follows the path that light takes on its journey through the functional eye, detailing the essential components of one of the smallest, yet most complex organs in the body. Many have attempted to emulate its abilities, but even top‐of‐the‐line digital single lens reflex cameras dare not compare with the elegant, efficient design infused in this multifaceted unit of anatomical machinery.

Key Concepts:

  • Accommodation refers to the changing of the shape of the lens as a result of the constriction or relaxation of ciliary muscles, in order to adjust its optical power to see clearly in the near distance. This process is used to bring objects into focus.

  • Eyes are part of the central neuronal system exposed to environmental stimuli. It captures and processes light signals to form discernible images.

  • Phototransduction refers to the process that creates a change in a photoreceptor's membrane potential due to the absorption of a photon by a photopigment molecule.

  • Retina is the outgrowth of the brain composed of multiple types of neurons and supportive cells that converts light signal into electrochemical impulses that are transmitted to the processing centres in the brain to form discernible images.

  • Glial cells are supporting cells of the nervous system. They provide support and protection for neurons by holding them in place, supplying nutrients and oxygen, isolating them from each other and removing the debris of dead neurons.

  • Neurons are a group of cells that can be electrically excited to process and transmit information by electrical and chemical signalling. They are the basic building blocks of the nervous system.

Keywords: eye; vertebrate; human; retina

Figure 1.

Schematic of a vertebrate eye. (a) Basic structures of the vertebrate eye have been colour coded. (b) Magnification of the anterior part of the eye, depicting the structures involved in aqueous humour circulation.

Figure 2.

Schematic view of the organisation of neurons and supportive glial cells in the vertebrate retina. (a) Organisation of retinal neurons within the retina. Six types of neurons are present in the vertebrate retina including rod and cone photoreceptors, bipolar, horizontal, amacrine and ganglion cells. (b) Organisation of retinal glial cells within the retina. Five glial cell types have been found in the vertebrate retina. Astrocytes are present in vascular retinas whereas oligodendrocytes are predominantly present in avascular retinas.

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References

Barbosa‐Sabanero K, Hoffmann A, Judge C et al. (2012) Lens and retina regeneration: new perspectives from model organisms. Biochemical Journal 447(3): 321–334.

Bodeutsch N and Thanos S (2000) Migration of phagocytotic cells and development of the murine intraretinal microglial network: an in vivo study using fluorescent dyes. Glia 32(1): 91–101.

Bruce V, Green PR and Georgeson MA (1996) Visual Perception: Physiology, Psychology and Ecology. London: Psychology Press.

Büssow H (1980) The astrocytes in the retina and optic nerve head of mammals: a special glia for the ganglion cell axons. Cell Tissue Research 206(3): 367–378.

Butt AM, Pugh M, Hubbard P and James G (2004) Functions of optic nerve glia: axoglial signalling in physiology and pathology. Eye 18: 1110–1121.

Carlson NR (2009) Structure and functions of cells of the nervous system. In: Carlson NR (ed.) Physiology of Behavior, 10th edn, pp. 28–67. Boston: Allyn & Bacon.

Charman WN (2008) The eye in focus: accommodation and presbyopia. Clinical and Experimental Optometry 91(3): 207–225.

Chen L, Yang P and Kijlstra A (2002) Distribution, markers, and functions of retinal microglia. Ocular Immunology and Inflammation 10(1): 27–39.

Cicero SA, Johnsonb D, Reyntjens S et al. (2009) Cells previously identified as retinal stem cells are pigmented ciliary epithelial cells. Proceedings of the National Academy of Sciences of the USA 106(16): 6685–6690.

Civan M (2008) The Eye's Aqueous Humor, 2nd edn. Amsterdam: Academic Press of Elsevier.

Coles BL, Angénieux B, Inoue T et al. (2004) Facile isolation and the characterization of human retinal stem cells. Proceedings of the National Academy of Sciences of the USA 101(44): 15772–15772.

Conway BR (2009) Color vision, cones, and color‐coding in the cortex. Neuroscientist 15(3): 274–290.

Daniels JT, Dart JK, Tuft SJ and Khaw PT (2001) Corneal stem cells in review. Wound Repair and Regeneration 9(6): 483–494.

Fahrenfort I, Klooster J, Sjoerdsma T and Kamermans M (2005) The involvement of glutamate‐gated channels in negative feedback from horizontal cells to cones. Progress in Brain Research 147: 219–229.

Fernandez DC, Pasquini LA, Dorfman D, Aldana Marcos HJ and Rosenstein RE (2012) Early distal axonopathy of the visual pathway in experimental diabetes. American Journal of Pathology 180(1): 303–313.

Fischer AJ, Scott MA, Zelinka C and Sherwood P (2010a) A novel type of glial cell in the retina is stimulated by insulin‐like growth factor 1 and may exacerbate damage to neurons and Müller glia. Glia 58(6): 633–649.

Fischer AJ, Zelinka C and Scott MA (2010b) Heterogeneity of glia in the retina and optic nerve of birds and mammals. PLoS One 5(6): 1–15.

Foster RG, Provencio I, Hudson D et al. (1991) Circadian photoreception in the retinally degenerate mouse (rd/rd). Journal of Comparative Physiology A 169(1): 39–50.

Gao L and Miller RH (2006) Specification of optic nerve oligodendrocyte precursors by retinal ganglion cell axons. Journal of Neuroscience 26(29): 7619–7628.

Ghazi NG and Green WR (2002) Pathology and pathogenesis of retinal detachment. Eye 16: 411–421.

Giannelli SG, Demontis GC, Pertile G, Roma P and Broccoli V (2011) Adult human Müller glia cells are a highly efficient source of rod photoreceptors. Stem Cells 29(2): 344–356.

Goldenberg‐Cohen N, Guo Y, Margolis F et al. (2005) Oligodendrocyte dysfunction after induction of experimental anterior optic nerve ischemia. Investigative Ophthalmology Visual Science 46(8): 2716–2725.

Henkind P, Hansen RI and Szalay J (1979) Ocular circulation. In: Records RE (ed.) Physiology of the Human Eye and Visual System, pp. 98–155. Hagerstown, MD: Harper & Row.

Inoue T, Coles BL, Dorval K et al. (2010) Maximizing functional photoreceptor differentiation from adult human retinal stem cells. Stem Cells 28(3): 489–500.

Kolb H (1997) Amacrine cells of the mammalian retina: neurocircuitry and functional roles. Eye 11: 904–923.

Kolb H (2003) How the retina works. American Scientist 91: 28–35.

Kolb H (2011) Simply anatomy of the retina. In: Kolb H, Nelson R, Fernandez E and Jones BW (eds) Webvision: The Organization of the Retina and Visual System. University of Utah. http://webvision.med.utah.edu/

Land MC and Fernald RD (1992) The evolution of eyes. Annual Review of Neuroscience 15: 1–29.

Lens Al (2008) Ocular Anatomy and Physiology, 2nd edn. United States: SLACK Incorporated.

Marmor MF and Wolfensberger TJ (1998) The Retinal Pigment Epithelium: Function and Disease. New York, USA: Oxford University Press.

Merbs SL and Nathans J (1992) Absorption spectra of human cone pigments. Nature 356: 433–435.

Newman EA (2004) Glial modulation of synaptic transmission in the retina. Glia 47(3): 268–274.

Nickerson PE, Emsley JG, Myers T and Clarke DB (2007) Proliferation and expression of progenitor and mature retinal phenotypes in the adult mammalian ciliary body after retinal ganglion cell injury. Investigative Ophthalmology Visual Science 48(11): 5266–5275.

Oyster CW (1999) The Human Eye. Sunderland: Sinauer Associates.

Palczewski K (2012) Chemistry and biology of vision. Journal of Biological Chemistry 287(3): 1612–1619.

Pressmar S, Ader M, Richard G, Schachner M and Bartsch U (2001) The fate of heterotopically grafted neural precursor cells in the normal and dystrophic adult mouse retina. Investigative Ophthalmology and Visual Science 42(3): 3311–3319.

Purves D, Augustine GJ, Fitzpatrick D et al. (eds) (1997) Vision: the eye. In: Neuroscience, 1st edn, pp. 179–198. Sunderland: Sinauer Associates.

Rompani SB and Cepko CL (2010) A common progenitor for retinal astrocytes and oligodendrocytes. Journal of Neuroscience 30(14): 4970–4980.

Salero E, Blenkinsop TA, Corneo B et al. (2012) Adult human RPE can be activated into a multipotent stem cell that produces mesenchymal derivatives. Cell Stem Cell 10(1): 88–95.

To CH, Kong CW, Chan CY, Shahidullah M and Do CW (2002) The mechanism of aqueous humour formation. Clinical and Experimental Optometry 85(6): 335–349.

Tsonis PA and Del Rio‐Tsonis K (2004) Lens and retina regeneration: transdifferentiation, stem cells and clinical applications. Experimental Eye Research 78(2): 161–172.

Volterra A and Meldolesi J (2005) Astrocytes, from brain glue to communication elements: the evolution continues. Nature Reviews Neuroscience 6: 626–640.

Wan QF and Heidelberger R (2011) Synaptic release at mammalian bipolar cell terminals. Visual Neuroscience 28(1): 109–119.

Whitehead AJ, Mares JA and Danis RP (2006) Macular pigment: a review of current knowledge. Archives of Ophthalmology 124: 1038–1045.

Wyse JP and Spira AW (1981) Ultrastructural evidence of a peripheral nervous system pattern of myelination in the avascular retina of the Guinea pig. Acta Neuropathologica 54: 203–210.

Yonemoto J, Noda Y, Masuhara N and Ohno S (1996) Age of onset of posterior vitreous detachment. Current Opinion in Ophthalmology 7(3): 73–76.

Zahs KR and Newman EA (1997) Asymmetric gap junctional coupling between glial cells in the rat retina. Glia 20(1): 10–22.

Zhang HR (1994) Scanning electron‐microscopic study of corrosion casts on retinal and choroidal angioarchitecture in man and animals. Progress in Retinal and Eye Research 13: 243–270.

Zhang Y and Stone J (1997) Role of astrocytes in the control of developing retinal vessels. Investigative Ophthalmology and Visual Science 38(9): 1653–1666.

Zhao X, Das AV, Soto‐Leon F and Ahmad I (2005) Growth factor‐responsive progenitors in the postnatal mammalian retina. Developmental Dynamics 232(2): 349–358.

Further Reading

Ahmad I, Tang L and Pham H (2000) Identification of neural progenitors in the adult mammalian eye. Biochemical and Biophysical Research Communications 270(2): 517–521.

Darwin C (1859) On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, 1st edn. London: John Murray.

Davson H (1949) The Physiology of the Eye. Philadelphia: Blakiston Company.

Frederic HM, Timmons MJ and McKinley MP (1999) The nervous system: general and special senses. In: Human Anatomy, 3rd edn, pp. 485–491. Upper Saddle River, USA: Prentice‐Hall.

Kessel D and Kardon RH (1979) Tissues and Organs: A Text‐Atlas of Scanning Electron Microscopy. San Francisco: WH Freeman.

Rister J and Desplan C (2011) The retinal mosaics of opsin expression in invertebrates and vertebrates. Developmental Neurobiology 71(12): 1212–1226.

Tropepe V, Coles BL, Chiasson BJ et al. (2000) Retinal stem cells in the adult mammalian eye. Science 287: 2032–2036.

Vilupuru AS, Roorda A and Glasser A (2004) Spatially variant changes in lens power during ocular accommodation in a rhesus monkey eye. Journal of Vision 4(4): 299–309.

Xu H, Sta Iglesia DD, Kielczewski JL et al. (2007) Characteristics of progenitor cells derived from adult ciliary body in mouse, rat, and human eyes. Investigative Ophthalmology and Vision Science 48(4): 1674–1682.

Zimmer C (2012) Our strange, important, subconscious light detectors. Discover Magazine, pp. 12–13. Jan/Feb 2012.

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Zhu, Jie, Zhang, Ellean, and Del Rio‐Tsonis, Katia(Nov 2012) Eye Anatomy. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000108.pub2]