1. As a convergence excess pt. attempts to work with variable vectograms, where would they have the most difficulty, with the numbers or with the letters? letters indicate BI demand, therefore it is expected that this pt. would have more difficulty with LETTERS
2. When working with the Brock string, what is the significance of the position of the crossing of the strings relative to the fused fixation ball? If it were behind the ball, what would this indicate? If it were in front of the ball, what would it indicate? Why do we call these misalignments "postures" and not phorias?
a. a gross fixation disparity indication; called a "posture"
- exo posture
- eso posture
d. because the patient has fused the fixation bead, it is less a phoria indication and more a VERY GROSS fixation disparity measure
3. What happened to the crossing of the string initially when the -3.00 D lenses were introduced? Why did this happen? ? as accommodative response is initiated, the bead will get clear and the string crossing would shift closer to the patient. AC/A dictates this eso shift
4. What did your partner have to do to bring the crossing back to the ball?
Increase fusional divergence so the NET VERGENCE RESPONSE REMAINS CONSTANT AND FUSION IS MAINTAINED
5. You introduce a 15 p.d. BO prism to a patient who, up to that time, had met all three BIG RULES. Where would you expect the strings to cross immediately after introduction of the prism? WHY? Before the pt. could make a vergence response, the strings would appear to cross significantly BEHIND the beads (the beads may even double). This is because the BO prism shifts the image temporally on the retina, creating an EXO fixation status. This is followed by a fusional convergence attempt to fuse the bead and at that time, the string crossing should shift to the fixation bead
6. How do you think SILO works? (this is a challenging one) Why is it important?
SI - As convergence demand ( numbers) increases, convergence cues give rise to the perception of the target coming closer. Retinal scaling mechanisms are responsible for the target to be scaled DOWN, even though retinal image size is constant (the target is stationary)
LO - As divergence demand (letters) increases, divergence cues give rise to the perception of the target going away. Retinal scaling mechanisms are responsible for the target to be scaled UP, even though retinal image size is constant (the target is stationary)
7. How will fixation disparity affect spatial localization and SILO with a vectogram?
A significant fixation disparity will alter spatial localization significantly. A patient with an eso fixation disparity would perceive a target with crossed disparity to have no disparity, or even uncrossed disparity. The end result would be that instead of floating in front of the vectogram, the image may appear flat, or even behind the vectogram!
8. Why would an observant doctor be able to detect suppression by observing the patient's eye movements during loose prism vergence therapy?
After introduction of the prism, there should be an observable convergence or divergence movement to the prism (convergence - BO; divergence - BI)
9. If the patient brings eccentric circles towards his/her body, what effect would it have on attempts to chiascopically fuse the targets? How about attempts to orthopically fuse the targets?
Chiascopic (crossed): increased convergence demand
Orthopic (uncrossed): increased divergence demand