applied anatomy of the eye 1

• what does each part of the eye do?

  Cornea -> refracts light, like a light prism. Air to solid has a high RI, biggest refraction at the corneal surface. Mentions liquid too

  Iris -> controls amount of light into the eye

  Lens -> focuses the light rays onto the back of the retina (focal plane, converge here)

  Retina -> phototransduction (rods and cones), photon of light -> electrical signals -> optic nerve

  Optic nerve -> transmits information to brain

  
• what are the three main components we need to see?

  1. clear cornea
  2. clear lens
  3. functioning retina and optic nerve to carry impulses
• what are the main layer of the cornea? what are the key differences between the innermost and outermost layers?

  epithelium and endothelium are nearly opposites

  
• for good refraction into they eye need smooth corneal surface

  disturbed corneal surface -> blurry vision

  endothelium is never replaced -> if gone may cause opacities

  keratocytes -> arranged in a way so that they don't interfere with light rays -> cornea looks transparent
• what is an eye without refractive error called? what are the two types of refractive error called? where do they land compared to the retina? which type of correctional lenses do they need?

  here

  
• what is astigmatism

  Astigmatism (uh-STIG-muh-tiz-um) is a common and generally treatable imperfection in the curvature of the eye that causes blurred distance and near vision. Astigmatism occurs when either the front surface of the eye (cornea) or the lens inside the eye has mismatched curves.
• what is astigmatism

  Astigmatism (uh-STIG-muh-tiz-um) is a common and generally treatable imperfection in the curvature of the eye that causes blurred distance and near vision. Astigmatism occurs when either the front surface of the eye (cornea) or the lens inside the eye has mismatched curves.

  
• list 4 things that can go wrong with the cornea (5th is. a surgery you could do)

  • corneal ulcer
  • corneal dystrophy
  • keratoconus
  • corneal odema
  • corneal graft
• what does this image show and why does it happen?

  corneal ulcer - contact lens, warm about ulcers à from poor hygiene, if pseudomonas the eye will perforate in 24hrs. Scaring and permanent loss of vision

  
• what is shown and why does it occur?

  corneal dystrophy - born with it, keratocytes not formed properly, under the epithelial layer and disrupts vision

  
• what is formed any why?

  keratoconus - non-inflammatory eye condition, round dome-shaped clear window of the eye (cornea) progressively thins causing a cone-like bulge to develop. This eventually impairs the ability of the eye to focus properly, potentially causing poor vision.

  keratocytes not formed properly, often see loss of collagen

  
• what is this and what causes it?

  corneal odema - endo cells cannot pump water out of cornea which causes swelling and odema

  
• what is this

  corneal graft - indicated by any of the other corneal diseases, or inflammation affecting vision

  
• what is the role of the lens? how does the lens achieve this ?

  Some refraction, accommodation and fine focus:Circumferential ciliary muscle contracts and relaxes to alter tension of lens capsule allowing lens to change shape.

  ciliary muscles work with suspensory ligaments to do so
• what is shown? what causes it?

  cataracts - clouding of the lens; as you age the lens thickens and the elastic capsule gets more full, eventually so many lens fibres it cannot change shape

  causes: Diabetes, Age, Corticosteroids, Congenital, Trauma

  tx with surgery

  
• name the key layers of the retina

  function of the RPE - look after photoreceptors

  selective barrier to and a vegetative regulator of the overlying photoreceptor layer, thereby playing a key role in its maintenance.

  
• what is the fovea?

  an area where the upper layers of the retina, the nerve fibres and ganglion are moved out of the way slightly to expose the photoreceptors (rods and cones), this makes it appear darker than other retinal cells
• which photoreceptors are found on the eye?

  Rods: scotopic vision

  Cones: photopic vision (+colour vision)

  Disks hold opsin molecules: rhodopsin in rods and iodopsin in cones. 3 different opsins present in all cones but one predominates each. They are sensitive to different wavelengths of light.

   

  "Blue" cones 420 nm,

  “Green" cones 530 nm,

   “Red" cones 560 nm.

  Light stimulates the isomerisation of cis-retinal in the photoreceptor, activating the opsin molecules leading to hyperpolarisation of the photoreceptor.

   
• which photoreceptors are found in eyes? what do they contain for phototransduction?

  Rods: scotopic vision

  Cones: photopic vision (+colour vision)

  Disks hold opsin molecules: rhodopsin in rods and iodopsin in cones. 3 different opsins present in all cones but one predominates in each. They are sensitive to different wavelengths of light.

   

  "Blue" cones 420 nm,

  “Green" cones 530 nm,

   “Red" cones 560 nm.

  Light stimulates the isomerisation of cis-retinal in the photoreceptor, activating the opsin molecules leading to hyperpolarisation of the photoreceptor.

   

  
• distribution of rods and cones

  fovea = only cones (colour information, high resolution) food for the fovea which prides sharp, central vision

  
• what can go wrong with the retina:

  • Colour Blindness

  • Retinal Vascular Occlusion

  • Diabetes

  • Macular Degeneration

  • Retinal Detachmeny
• prefixes and suffixes in colour blindness:

  Prot-      Red (L) cones

  Deuter-     Green (M) cones

  Trit-       Blue (S) cones

  Anomaly  (malfunctioning)

  Anopia     (absent)
• how to test for colour blindness -> ishihara plates
• Central Retinal Artery Occlusion (CRAO) occurs when the retina loses blood supply, retina thins and dies, poor vision

  fundus photography - see 'cherry-red' spot, pallor from infarct

  
• cotton wool spots = sign of ischaemia
• anatomy for retinall vascular occlusions

  CRAO - central retinal artery occlusion

  Central retinal artery occlusion

  
• Central Retinal Vein Occlusion

  Venous thrombosis leading to haemorrhage, oedema, cotton wool spots and neovascularisation

  
• Diabetic Retinopathy

  micro aneurysms -> Microvascular leakage + occlusion -> oedema, exudation and haemorrhage in inner retinal layers. This causes Ischaemia which leads to neovascularisation (VEGF).

  
• what is this image of?

  here

  
• what causes dry AMD?

  cause unknown

  Build-up of waste products from photo-transduction. May lead to atrophic changes.

  degeneration of the macular
• what causes dry AMD?

  cause unknown

  Build-up of waste products from photo-transduction. May lead to atrophic changes.

  degeneration of the macula progressively

  
• what does this image show?

  can see loss of fovea and macula, see the atrophy/ loss of photoreceptors and inner retinal layer

  
• what can stop the eye from seeing?

  below a summary of the first lecture

  
• How does retinal detachment happen

  PVD extends and cause a passage behind the retina because a tear in the retina. fluid leaks in behind this and under gravity separates the retina from the sclera -> retinal detachment

  tear between the photoreceptor layer and RPE
• what does this show?

  retinal detachement

  
• what causes Wet AMD?

  Inflammation and hypoxia lead to choroidal/sub-retinal neovascularisation (VEGF) which breaks through into the outer retinal layers causing oedema and haemorrhage.

  This causes distorted vision as photoreceptors are displaced.

  anti-VEGF works on wet

  
• why does distortion occur in wet AMD?

  Pixels: Each cone responsible for seeing one part of face and that is mapped exactly in the occipital cortex -> oedema separates the cones their pixels will be in different places -> The brain assembles the image as though cones are in correct place therefore image appears distorted
• Optic nerve problems:

  •Inflammation (optic neuritis)

  •Glaucoma

  •Ischaemia

  •Compression

  •Papilloedema
• symptoms of optic nerve problems:

  •Reduced visual acuity. 

  •Altered colour vision

  •Visual field defects

  •Relative Afferent Pupil Defects
• Optic neuritis

  Inflammation of optic nerve, variable visual loss including colour vision problems but usually recovers within a few months - loss is variable.

  Can be related to Multiple Sclerosis (50%) or be post-viral 

  may look noramal swollen orpale