visual

• Visual System


  The system responsible for vision in organisms
• Anatomy of the eye


  • Cornea
  • Lens
  • The retina
  • Muller cells
  • Bipolar cells
  • Horizontal cells
  • Amacrine cells
  • Retinal ganglion cells
  • Myo/Nog cells
  • Photoreceptors

  
• Visual pathways


  The neural pathways that transmit visual information from the eye to the brain
• Retinal vasculature and diseases


  The blood vessels in the retina and associated diseases
• Saccadic Eye Movement


  The series of small, quick movements the eye makes to "take in" the whole image
• Human beings are the only primates with white sclera
• Only primates have a macula and fovea
• Corneal transplant has no rejection and no blood flow
• Cornea


  1/6 volume of the orbit is covered by cornea, while the other 5/6 is covered by sclera
• We have an inverted retina
• General Structure of the Cornea


  • Epithelium layer: Many nerve endings, absorb oxygen and nutrients from tears
  • Bowman's membrane: Collagen fibers
  • Stroma: Water and collagen in specific order for light to go through
  • Endothelium: Non replaceable cells responsible for keeping balance of fluids from the AC to the stroma
• Ciliary body


  Houses Choroid plexus which secrets aqueous humour: 2μl/min. It gets replaced every 2hrs. Pressure is generated by fluid production and relieved by reabsorption.
• Trabecular meshwork


  Resistance to outflow creates a pressure of ~ 15mm Hg. Intraocular pressure maintains the shape of the eye
• Circulation of Aqueous Humour in the Anterior Cavity


  • Ciliary epithelium
  • Posterior chamber
  • Anterior chamber
  • Trabecular meshwork
  • Canal of Schlemm communicates with the venous drainage of the eye
• Glaucoma


  A disease caused by increased intraocular pressure
• Luxation of lens


  Dislocation of the lens
• The Lens


  • Parts: Capsule, Epithelium, Fiber cells, Nucleus
  • It changes shape (ciliary body, suspension filaments) to change the focal distance to adjust to objects at different distances: Accommodation
  • 3.5-5mm thickness X 6.5-9mm equatorial weight 250mg at 40yo
• Cataracts


  Cloudiness of the lens
• Santiago Ramòn y Cajal won the Nobel prize in Medicine in 1906
• Important structures in the Retina


  • OS: Outer Segments of Photoreceptors
  • IS: Inner Segments of Photoreceptors
  • ONL: Outer nuclear layer
  • OPL: Outer Plexiform layer. Synaptic
  • INL: Inner nuclear layer
  • IPL: Inner plexiform layer. Synaptic
  • GCL: Ganglion cell layer
  • NFL: Retinal nerve fiber layer
• Cells in the Retina

  • Photoreceptors: Neuronal cells. Cones and Rods
  • Müller cells (MC): Non-neuronal glial cells
  • Bipolar cells (BC): Neuronal
  • Amacrine cells (AC): Neuronal
  • Horizontal cells (HC): Neuronal
  • Ganglion cells (GC): Neuronal
  • Myo/Nog cells (M/N): Non-neuronal
• Myo/Nog cells


  Non-neuronal cells that are neuroprotective and can slow down certain kinds of blindness
• Photoreceptors


  • Rods: Used for scotopic vision (low light), very light sensitive, low visual acuity
  • Cones: Used for photopic vision (high light), not very light sensitive, high visual acuity
• Cone pigments (Photopsins)


  Tune the receptor's absorption to a region of the spectrum
• Rod pigments (Rhodopsin)


  Responsible for monochromatic vision in low light
• Types of color blindness


  • Protanopia: no "red" pigment
  • Deuteranopia: no "green" pigment
  • Tritanopia: no "blue" pigment
• Fovea


  Concentrated area of cones for visual acuity, comprises central 2% of retina, located within the macula lutea
• Peripheral Retina


  The area of the retina outside the fovea
• The optic disk and fovea are labelled on the image
• Retinitis Pigmentosa


  Genetic disorder that affects mostly rod photoreceptors, leading to complete blindness by adulthood
• Age Related Macular Degeneration


  The layer behind the RPE thickens and yellow deposits appear, leading to hemorrhages and loss of vision in the macula
• Retinal Detachment


  Separation of the retina from the underlying choroid, requiring urgent care
• Diabetic Retinopathy


  New blood vessels form, leading to hemorrhages that can cause detachment and blindness. Treated with anti-VEGF therapies and laser treatments
• Visual Pathways


  Ganglion cells -> Optic chiasm -> Lateral geniculate nucleus -> Occipital Lobe
• Visual Field Defects


  Damage to parts of the visual pathway leads to corresponding blind spots in the visual field