Negative relative accommodation (NRA) was proposed by Joseph Kearney of Oxford University in 1967 as a measure of the maximum ability to relax accommodation while maintaining clear, single binocular vision.
It is an indirect measurement of fusional vergence in binocular vision.
[1] This measurement is typically obtained by an orthoptist, ophthalmologist or optometrist during an eye examination using a phoropter.
After the patient's distance correction is established, the patient is instructed to view small letters on a card 40 cm from the eyes.
The examiner adds convex lenses in +0.25 increments until the patient first reports that they become blurry.