Primary Optometry Lab 6163 (Wensveen); Fixation Disparity Practice Questions:
1) During measures taken with the Mallett box at near, which of the 4 classic components of vergence contribute to the measured vergence position?
There is always TONIC vergence, because the measure is at near there will be ACCOMMODATIVE convergence and convergence due to PROXIMAL vergence, but there will also be FUSIONAL vergence because the Mallett box measures the associated phoria which is the prism to correct for the fixation disparity which is the deviation when you are fused. 2) The Mallett box measures the same function as the:
The Mallett box measures the associated phoria, which is prism to correct for the fixation disparity; the other instrument that you will use to measure the associated phoria is the Wesson Card. 3) Your lab partner has plotted her forced-vergence fixation disparity curve and has decided it is a type III. The x-axis intercept is zero. What would her fixation disparity be?
The x-axis intercept is the associated phoria (prism to correct for the fixation disparity), and if it is zero, then there is no fixation disparity. 4) In the lab you used the Wolff card to measure your own baseline fixation disparity. Remember that the right eye saw the top line, and the left eye saw the array of lines on the bottom. If you saw the Wolff card like: l
The direction of the correcting prism would be: BASE OUT
5) In the same lab we used the Wolff card to measure fixation disparities that we were trying to elicit in our subjects. The right eye saw the top line, and the left eye saw the array of lines on the bottom. If the subject reported seeing the Wolff card like: l
l l l l l l l
C B A 0 1 2 3 The fixation disparity would be: 17 arcminutes ESO
The direction of prism used to create this fixation disparity would be: BASE IN
6) You are using the Wesson card to assess the ocular alignment of your patient. He sees the black arrow with his right eye and the array of colored lines with his left eye. He tells you the black arrow is pointing to the yellow line that is to the right of the center red line. He has an ESO fixation disparity (kind & direction of deviation) that could be neutralized with BASE OUT (direction) prism.
7) You decide to test the same patient with the Mallett box at near. If the right eye sees the top line and the left eye sees the bottom line, how do you expect your patient to see the lines?