A Comparison Of Risley And Bar Vergences.

Recently mechanisms but there has been interest in disparity measurement of them clinically has not and vergence kept pace. Right now the most popular way of measuring fusional vergence reserves is with the Risley prisms in a phoropter. However, recently Vaegan and Pye demonstrated the use of a motorized prism stereoscope to measure vergences at near but data from their study agree with reported values for break and recovery for both convergence and divergence measured with prisms in the phoropter.
This is fine but ideally it would be better to measure vergences in a more natural environment . The Beren's 15 prism bar allows this. A patient has peripheral cues and so is more aware of his surroundings and normal spatialization. Another reason the prism bar is more natural is that a patient must make step vergence movements instead of a ramp type movement with a Risley prism. When a person looks from far to near, such as from
the blackboard at school to his paper he is taking notes on, he makes a step vergence.
Probably the biggest advantage of the prism bar is its use in children. The break and recovery points can be viewed objectively by observing the eye-turn and fusional movements respectfully. The only problem with this is the difficulty in seeing small angle loss of
fusion. In this case a subjective response is required. There have been studies done which have found normals for near and far vergences with Risley prisms in a phoropter. What I want to do in this study is compare Risley prism and bar prism vergences and also take into consideration eye dominancy.