Examination: Visual Acuity

Assessing visual acuity is an important skill and is often tested in OSCEs. Ensure that you know how to progress through the examination if the patient does have imparied acuity, and know how to correctly record the results.

  • Wash hands
  • Introduce and explain
  • Ask permission

Assessing long distance vision:
  • Ask the patient whether they use glasses or contact lenses for distance vision. If so they should keep these on for the examination
  • Position the patient 6m from the Snellen chart (an example of the chart can be found here)
  • Ask patient to cover one eye and read lowest line on the chart
  • If they cannot do this, ask them to read the next line above this
    OSCE-Aid Tips

    It is possible in an exam that you will have a mini-Snellen. This will look like a normal Snellen however it will be smaller. When using a mini-Snellen you must ask your patient to stand 3m from the chart and not 6. However acuity will still be recorded as 6/the number of the line readable on the chart, as normal.

  • Repeat this until you reach a line they can read completely
  • Do the same with the other eye
  • If vision isn't perfect (i.e.: 6/6):
    • Use pin hole test to see if vision improves
    • If it does, then the problem with sight is an uncorrected refractive error
  • Record data
    • As 6/number by line on chart that they could read successfully (e.g. 6/5)
    • If the patient is able to read most of the letters on a line but gets a minority wrong then the acuity should be recorded as 6/the number of the line read the number of letters read incorrectly. For example if the patient read line 9 but got 1 letter wrong their acuity would be 6/9-1.
    • If the patient can read only a minority of letters on a line then their acuity should be written as 6/the number of the next line up + the number of letters they read correctly on the line they could not fully read. For example if the patient reads only 2 letters on line 6 correctly their acuity should be recorded as 6/9+2
    • A lettered suffix should then be added as appropriate:
      • UA if unaided
      • C Gl for wearing glasses
      • S Gl for not wearing glasses, but normally wears them
      • C CL for wearing contact lenses
      • PH for improved sight with pin hole test
  • If can't read top line of Snellen chart, move them forwards to 3m from the chart (or half the distance, if using a small Snellen chart), and record this as 3/number by line on chart
  • If no letters can be seen by the patient, procede to examine each eye in turn with the following tests:
    • Ask them to count fingers (hold your hand in front of them). If patient able, record acuity as CF
    • If they cannot count your fingers then wave your hand in-front of patient. If patient detects hand motion, record acuity as HM
    • If the patient cannot detect hand motion then shine a light into their eye (in all four quandrants of each eye). If patient can perceive light record acuity as LP
    • If the patient has no light perception you can record acuity as NLP

Assessing short distance vision:
  • Cover one eye and read from the set text for assessing acuity (N5 smaller than N8)
  • Read from largest to smallest
  • Record smallest text size seen
  • Do the same with other eye

To conclude the examination:
  • Assess the back of the eye using an ophthalmoscope
  • Examine the 3rd, 4th and 6th cranial nerves
  • Thank the patient