Blindness

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Ocular causes

Definition

Blind

  • Inability to count fingers at a distance of 3m or less
  • ≤ 3/60 in both eyes
  • OR restrictions of the visual field

Partially sighted

  • Inability to count fingers at a distance of 6m or less
  • ≤ 6/60 in both eyes

Prevalence

  • Less than 20% of legally blind people are totally blind
  • Most of these can distinguish light from dark
  • 70% of people with visual disability are >75 y.o.
  • 8% of people with visual disability are born with the disability
  • 60% of people with visual disability due to other serious illness
  • 25% of people with visual disability are employed

Dysfunction

Cornea

  • Oedema - injury / degeneration of corneal endothelium
  • Stromal scar - chemical / physical / infectious agent causing fibroblastic proliferation, irregular deposition of collagen, and neovascularization

Aqueous outflow pathway

  • increased resistance to outflow and raised intraocular pressure (IOP)
  • see glaucoma

Lens

Retina

  • detachment
    • rhegmatogenous - tear in the neurosensory retina that allows vitreous fluid to seep beneath the retina
    • exudative - fluid or abnormal tissue accumulates beneath the intact neurosensory retina
    • tractional - fibrous or fibrovascular tissue within the vitreous pulls the neurosensory retina away from the retinal pigment epithelium
  • retinoblastoma in children
  • pre-retinal neovascularization (as in diabetes)
  • hereditary degeneration (retinitis pigmentosa)
  • subretinal neovascularization and scarring (as with age-related macular degeneration)

Choroid

  • site of most intraocular tumours in adults (primary or metastases)

Optic nerve

  • papilloedema
  • optic neuritis
  • tumours

Resources