Visual Acuity

Overview

• • How to Assess

  • Ask the patient to cover one eye, look at a Snellen chart (wall-mounted at 6m or handheld at arm's length) and identify the smallest line that they can read.
• If the patient wears corrective lenses, perform the test with and without them.
• If the patient's visual acuity is poor, use a pin hole over their eye to test for refractive error.

• • Causes of Poor Visual Acuity

  • Refractory error
  • Corneal opacification - cataract, infection, trauma
  • Vitreal opacification - intraocular haemorrhage
  • Retinal disorders - macular degeneration, retinal detachment, diabetic retinopathy, retinal artery occlusion
  • Optic nerve disorders - glaucoma (raised intraocular pressure), ischaemia, optic neuritis
  • Intracranial disorders - pituitary disorders, aneurysm