Eye

• What is the function of the eye?


  vision
• What is the structure of the eye?

  eyeball and accessory structures (conjuctiva , eyelids , lacrimal galnd , extraocular muscles)
• What are the chambers of the eye?

  Anterior : between cornea and iris , aqueous humor

  
  

  Posterior: Between posterior surface of iris and the anterior surface of the lens , aqueous humor

  
  

  Vitreous chamber: between the posterior surface of the lens and the neural retina , vitreous humor
• What are the layers of the eye?

  Three concentric layers: fibrous layer (sclera and cornea) , vascular layer (uvea; choroid , ciliary body and iris) , sensory layer (the retina)
• What are the characteristics of the fibrous layer?


  Cornea: covers anterior part of eye , convexity , transparent

  
  

  Sclera: composed of dense fibrous connective tissue
• How many layers in the cornea?


  5

  1)corneal epithelium

  2) bowman's membrane

  3) corneal stroma/substantia propria

  4) Descemet's membrane

  5) Corneal endothelium
• What are the characteristics of the corneal epithelium?


  Non keratinized stratified squamous epithelium , extreme sensitivity to touch (numerous nerve endings) , high regenerative capacity , UV protection , microvilli in the surface
• What are the characteristics of the bowmans membrane?


  Anterior basement membrane , strength to the cornea and barrier to infections , collagen fibers randomly oriented , no regeneration
• What are the characteristics of the corneal stroma?

  60 layers of parallel collagen bundles oriented at right angles , avascular tissue , flattened fibroblast between layers
• What are the characteristics of the descemet's membrane?

  Posterior basement membrane , regenerates after injury
• What are the characteristics of the corneal endothelium?


  Single layer of squamous cells , limited proliferative capacity
• What is are the characteristics of the limbus


  transition zone between the cornea and sclera , difficult to define , no bowman's membrane , epithelium becomes more stratified , stroma become vascular and less organized
• How does the cornea recieve nutrition?


  diffusion from capillaries in the limbus , aqueous humor and tear liquid
• What are the functions of the limbus?


  Nutrition of the cornea (vascular vessels) , regeneration of the corneal epithelium (stem cells) , it drains the aqueous humor from the anterior chamber, system of irregular endothelium lined channels (trabecular meshwork) , merge to form the scleral venous sinus/canal of schlemm that encircles the eye
• What are the characteristics of the sclera?


  dense connective tissue: fibroblast , collagen fibers , elastic fibers , blood vessels and nerves

  
  

  Functions: protection of the eyeball and shape
• What are the characteristics of the vascular layer?


  Choroid: loose well vascularized connective tissue , contains melanocytes

  
  

  Ciliary body: encircles the lens

  
  

  Iris: anterior extension
• What are the layers of the choroid?


  1) choroidal stroma: large arteries and veins , fibroblast , fibers , few smooth muscle cells and melanocytes

  2) Choriocapillary layer: inner , rich microvasculature, fenestrated

  3) Bruch's membrane: thin extracellular sheet , collagen and elastic fibers

  
  

  Functions: absorption of scattered light , nutrition of the retina
• What is the structure of the ciliary body?


  1) ciliary muscle: three groups of smooth muscle fibers , contractions affect the shape of the lens

  2) Ciliary processes: 75 ridges projecting into the posterior chamber , ciliary epithelium: double layer of columnar epithelial cells , nonpigmented in contact with aqueous humor. characteristics of a fluid transporting epithelium , outer heavily pigmented , secretion of aqueous humor

  3) Ciliary zonules : system of radially oriented fibers produced by the nonpigmented cells of the ciliary processes:RER and golgi , suspensory ligament of the lens
• What are the characteristics of the aqueous humor?


  Produced by the ciliary epithelium lining the ciliary processes , fluid transporting epithelium: complex cell to cell junctions , lateral and basal plications , NA+/K+ ATPase pumps

  Similar in ionic composition to plasma but contains less than 0.1% protein
• What are the functions of the ciliary body?

  Aqueous humor production , suspension of the lens , blood aqueous barrier
• How do our eyes accomodate to our visual needs?


  Far object: ciliary muscles relax , more tension in suspensory ligaments , lens pulled thinner

  
  

  Near object: ciliary muscle contract , tension lost in suspensory ligaments , lens pulled spherical
• What are the characteristics of the iris?


  Most anterior part of the vascular layer , it forms a contractile diaphragm , pupil is the central aperture of the disc , anterior surface of the iris is in contact with aqueous humor (dense layer of fibroblast and melanocytes , no epithelium) , stroma of the iris (loose connective tissue , melanocytes , microvessels) . sphincter pupillae muscle: smooth muscle located in the stroma near the pupillae margin
• What are the characteristics of the pigment in the iris?


  Posterior pigmented epithelium: posterior surface by highly pigmented cells ,anterior pigmented myoepithelium: myoepithelial cells , dilator pupillae muscle
• What are the characteristics of the crystalline lens?


  Transparent , avascular , biconvex structure suspended immediately behind the iris , it focuses light on the retina
• What are the components of the crystalline lens?

  Lens capsule , subcapsular epithelium , lens fibers

  
  

  (cytoplasm fills with crystallins , organelles and nuclei are autophaged)
• What are the components of the retina?

  Photosensitive region:posterior to ora serrata , it lines the posterior part of the eye

  neural retina: contains the photoreceptors

  Pigmented layer: simple cuboidal epithelium attached to bruchs membrane and the choroid capillary lamina
• What is the structure of the nonphotosensitive region?


  Anterior to ora serrata

  ciliary body: inner epithelium (non pigmented , it is continuous with sensory layer of retina)

  outer epithelium: Continuous to the pigmented

  iris: epithelium covering posterior iris
• What are optic disc and fovea centralis?

  Optic disc: site optic nerve joins retina , blind spot

  
  

  Fovea centralis: area of gretest visual activity , high concentration of visual elements
• What are the layers of the retina?


  1) pigmented layer

  2) rod and cone layer

  3) outer limiting layer

  4) outer nuclear layer

  5) outer plexiform layer

  6) inner nuclear layer

  7) inner plexiform layer

  8) Ganglionic layer

  9) nerve fiber layer

  10) inner limiting layer
• What are the cell types found in retina?


  pigmented epithelium

  Neurons: photoreceptors (cones and rods) , conducting (bipolar and ganglion cells) , association (horizontal and amacrine cells)

  Supporting glial cells (muller's cells)
• What are the characteristics of the retina pigmented epithelium?


  Outer layer , not part of the neural retina , single layer of cuboidal pigmented cells , basal nuclei , projections in their apical surface associated with tips of photoreceptors , melanin granules in projections , phagocytic vacuoles , secondary lysosomes , peroxisomes and sER , junctional complexes
• What are the functions of the retina pigmented epithelium?

  to absorb scattered light , protective blood retina barrier, it isolated retina photoreceptors from vascular choroid , regulates ion transport between the compartments, visual pigment resynthesise (vitamin A regeneration) , phagocytosis of shed material from photoreceptors , support the retina
• What are the characteristics of the rod and cone layer?


  Photoreceptor cells , each rod and cone have three parts:

  outer segment (site of photosensitivity , highly modified cilium) , connecting stalk (basal body) , inner segment (metabolic machinery)
• What are the differences between rods and cones?

  Rods: free floating disks , more senssitive to low wavelength , slow adaption to light intensity , more sensitive to low light , black and white picture , 125 million , visual pigment rhodopsin

  
  

  Cone: folds ,

  more sensitive to high wavelength , quick adaption to light intensity , less sensitive to low light , colour vision , 7 million , high density in the fovea , iodopsin
• What is the process of phototransduction?


  Rhodopsin

  opsin:transmembrane protein different in rods and cones

  Chromophore retinal

  When light reaches rhodopsin theres a change in conformation of chromophore from cis to trans

  retinal is released inducing an action potential
• What are the characteristics of colourblindness?


  Inhereted disorder , recessive mutations in genes for one or more iodopisns ,more frequent in men
• What are the characteristics of the outer limiting layer?

  It is a row of adherent junctions that attach the apical ends of muller's cells to each other and to the rods and cones
• What are the characteristics of the outer nuclear layer?


  Contains the nuclei of retinal cones and rods , cone nuclei stains lightly and are larger and more oval that rod nuclei
• What are the characteristics of the outer plexiform layer?


  Contains fibers and synapses of bipolar neurons , rod and cone cells , horizontal cells , area of synapse
• What are the characteristics of inner nuclear layer?


  Contains nuclei of bipolar neurons , horizontal cells , amacrine cells , muller's cells