Visual Acuity Presentation in General Practice

details how to examine vision and common conditions that may effect that. short revision - not intended to be a comprehensive guide

1. Visual acuity Testing Salman N Sadiq

2. What is Visual acuity and why do we measure it? Visual acuity testing is a measurement of the resolving power of the eye i.e. the ability of the eye to create two separate images of two objects very close together Uncorrected refractive error (myopia/hyperopia/astigmatism) is the commonest cause of reduced acuity – this is corrected via prescription glasses Any condition affecting the light pathway can lead to reduced visual acuity This may be tear film, cornea, lens, vitreous humour, retina, optic nerve or brain

3. Philos2000, CC BY-SA 3.0 <https:// creativecommons.org /licenses/by- sa /3.0>, via Wikimedia Commons

4. Snellen chart

5. Measuring Visual acuity Make sure the room is well lit and the patient is seated comfortably at the appropriate distance away from the chart The chart will tell you the testing distance, normally is 6 metres Our chart today is a 3 metre chart The patient should wear their own distance glasses if they have one We want to measure the visual loss due to pathology other than refractive error

6. Measuring Visual acuity Ask the patient read down the chart up to the lowest line they can read Each eye is tested separately If the patient is unable to continue, then ask them to look through a pinhole If the vision improves looking through a pinhole then it suggests that there is a degree of refractive error (other pathology could still be present)

7. Recording acuity For a Snellen chart, the acuity is recorded as a fraction: Write down which eye was tested The top number is the test distance The bottom number is the smallest line the patient was able to read (check the labelling on the chart) If they managed to answer up to two letters incorrectly, you can write a (-2) to indicate this. If more than two incorrect, the line above should be recorded instead. Right down if this vision was with glasses, unaided (UA) or with pinhole (PH)

8. Recording acuity A patient wearing their prescription glasses was able to read up to the “HOV ” line on the Snellen above using their right eye, with two more lines visible using a pinhole.  I would record this as: Right eye 6/36 with glasses, 6/18 with pinhole or VA RE 6/36 c gls , 6/18 c PH

9. Recording acuity Using their left eye with glasses, they could see almost all of the letters of the fourth line, but got one wrong. There was no improvement when using a pinhole. Record this as: Left eye 6/15 (-1) with glasses, no improvement with pinhole or VA LE 6/15(-1) c gls , NIPH

10. Tips If you don’t have an occluder, ask the patient to use the palm of their hand to cover their eye Not their fingers! Or a piece of A4 paper folded over twice A simple pinhole can be made via piercing a piece of card with a pen

11. Unable to read the chart? Decrease the testing distance to 3 metres. If they are able to see the top letter now then record this as 3/ rather than 6/ because the numerator is always the testing distance. Try and see if they are able to count the number of fingers you’re holding up. This is recorded as “counting fingers” or CF vision. Failing that, you should see if they are able to see the movements of your waving hand. This is recorded as “hand motion” or HM vision. Failing that, you should see if they are able to see the presence of a light from a pen torch. This is known as “perception of light” or PL vision.

12. Time to practice