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
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