Measuring visual acuity in the ED

Correctly measured and documented visual acuity (VA) is an essential part of the assessment of a patient with an eye-related complaint.

Distance glasses or contact lenses?

• If yes, the patient should wear them.
• If left at home: document this.
• Do not measure VA with reading glasses.

Measuring VA with Snellen chart:

• Patient sitting in testing chair.
• Adequate illumination.
• Test each eye separately.
• Cover other eye with occluder/hand.
• Ask patient to read from top letter.
• Keep going until they cannot read the line clearly, making multiple errors.

Can't read the 6/6 line? Use pinhole:

• See if patient can read any further down the chart.
• This corrects for refractive error (mimicking glasses use).

Cannot read the top letter? Progressive steps:

1. Test 1 metre distance from the chart.
2. Count fingers held up at 1 metre: Counting Fingers (CF) at 1m.
3. See a moving hand: Hand Movements (HM).
4. See a pen torch light: Light Perception (LP).
5. Unable to perceive light: No Light Perception (NLP).

Documentation of VA:

• VA is expressed as a ration recorded as X/Y.
• X=testing distance, Y=line containing the smallest letters the patient identifies. e.g.
  • VA R=6/12, 6/6 with pinhole.
  • VA L=6/36, not improved with pinhole.
  • e.g. VA R=6/9 with glasses.
  • VA L=CF at 1m.

Link to YouTube tutorial.