Chapter 2- Measurement of visual acuity I (2) Flashcards
What is a pinhole?
A pinhole is used to determine whether reduced vision is caused by refractive error.
If reduced vision is due to refractive error, what will the pinhole show?
It will show that the visual acuity has improved.
When would you assess vision through the pinhole?
When visual acuity is less 6/9 (LogMAR= 0.2)
What does the pinhole do?
It removes the effects of refractive error which focuses light better.
If visual acuity improves through the pinhole, then…
reduced vision is due to refractive error.
If visual acuity doesn’t improve through the pinhole then…
it is likely that the back of the eye is affected
What would you do if vision/VA is less than 6/60?
You would use a portable Landolt C or E
At what distances would you test vision using the portable landolt letters?
You would test at 3m, then 2m and then 1m.
What would you do if you are measuring vision/VA from less than 1m?
You would tell a patient to count fingers and use hand movement.
What is used for testing near vision?
A specifically designed reading card with different text sizes.
How would you test near vision?
You would test each eye separately using their reading glasses if applicable.
How would you record for near test vision?
Record the smallest size that the patient can read, e.g, N8 at 25 cm slowly with ease.
What is the ‘N’ notation for near reading and the number after it?
the N indicates that the measurement is for near reading
The number following the N is the point size of the print.
What will patients with poor contrast sensitivity struggle with?
They will struggle to see text on different coloured backgrounds.
What would you use in order to measure contrast sensitivity?
You would use the Pelli- Robson letter chart.
