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
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------