What is vergence facility?

Vergence facility, defined as the number of cycles per minute that a stimulus can be fused through alternating base-in and base-out prisms, attempts to capture the ability of the fusional vergence system to respond rapidly and accurately to changing vergence demands over time.

What is vergence in Optometry?

A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision.

How is vergence facility measured?

Vergence facility was measured with a flipper of prism combination 3ΔBI/12ΔBO for one minute period. The two accommodative tests were done both monocular and binocular, in the order of right, left and binocular. Results: The mean amplitude of accommodation in this study was 13.5 ± 1.9 D.

What is NRA and PRA?

The two tests of positive relative accommodation (PRA) and negative relative accommodation (NRA) measure the maximum ability to stimulate accommodation while maintaining binocular single vision. These two tests can also help with indirect evaluation of fusional vergence.

What is fusional vergence dysfunction?

Fusional vergence dysfunction (FVD) is a binocular vision disorder with an unknown etiology.1 In this condition, accommodative convergence/accommodation (AC/A) ratio is normal, distance and near heterophorias are within the expected values, and accommodative function is intact, but fusional vergence findings are …

What is vergence movement?

Vergence refers to the simultaneous movement of both eyes in opposite directions to obtain single binocular vision. When the eyes rotate towards each other (convergence) the angle of eye increases and when the eyes rotate away from each other (divergence) the angle becomes smaller (Figure 1).

How do you test for vergence?

Vergence ability. To evaluate vergence ability, measure either smooth vergence using Risley prisms in the phoropter or step vergence using prism bars outside of the phoropter.

What do you mean by vergence?

Definition of vergence the turning motion of the eyeballs toward or away from each other.

What is positive relative vergence?

Positive relative accommodation (PRA) in biology, is a measure of the maximum ability to stimulate eye accommodation while maintaining clear, single binocular vision. This measurement is typically obtained by an orthoptist, ophthalmologist or optometrist during an eye examination using a phoropter.

How do you do NRA and PRA?

To determine the appropriate near correction for the patient, consider the negative relative accommodation (NRA) and the positive relative accommodation (PRA) findings. For example, if the NRA was +2.75D and the PRA was 0.75D, this would suggest an add of +1.00D to balance the NRA and PRA.