Credit: Les Black

A US review found on average, clinical Snellen visual acuity (VA) is one to two lines worse than electronic Early Treatment Diabetic Retinopathy Study (eETDRS) protocol refraction and VA testing, which researchers said may partly explain why clinical practice does not always replicate clinical trial results.  

Analysing data from 1,016 eyes from 74 centres, researchers led by Dr Carl Baker, founder of Hilton Head Retina Institute, found eyes with lower clinical measurements and eyes tested without clinical refraction tended to have larger differences. On average, the difference between clinical and protocol VA was 1.3 letters smaller for every line (five letters) increase in clinical VA, they said.  

Researchers concluded refracting eyes in the clinic may benefit patients when determining treatment plans and study referrals based on vision.