Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of...
-
Upload
kent-telling -
Category
Documents
-
view
224 -
download
7
Transcript of Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of...
![Page 1: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/1.jpg)
Fixation Disparity
![Page 2: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/2.jpg)
Fixation Disparity
Fixation disparity is a small error in the visual system.
Occurs as a result of Panum’s fusional area
Small error-minutes of arc 6 to 12 minutes of arc
![Page 3: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/3.jpg)
![Page 4: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/4.jpg)
Fixation Disparity
Depends of type of stimulus, larger for lower spatial frequencies.
Acts as stimulus for the vergence system Balance between the convergence and
divergence Compensation for phoria Accommodative inputs
![Page 5: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/5.jpg)
Measuring Fixation Disaparity
Calculate fixation disparityFD = 2a/2.9 x 10-4 x b/b2a=PDb=target distance b=difference between target distance and
convergence distance2.9 x 10-4 = conversion factor from radians to
min of arc
![Page 6: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/6.jpg)
Example
![Page 7: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/7.jpg)
Can be measured at distance and near Horizontal deviation Vertical deviation Uses nonius lines with a fusion lock Takes advantage of vernier acuity
![Page 8: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/8.jpg)
How Tests Work
Diagrams of Exo, Eso and Vertical Change nonius lines to compensate for FD Use prism to compensate for FD
![Page 9: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/9.jpg)
Sheedy Disparometer
![Page 10: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/10.jpg)
Mallet Unit
![Page 11: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/11.jpg)
Wesson Card
![Page 12: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/12.jpg)
![Page 13: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/13.jpg)
Saladin Card
![Page 14: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/14.jpg)
Saladin Card
![Page 15: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/15.jpg)
Saladin Card
![Page 16: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/16.jpg)
Generating a forced vergence disparity curve Put prism in place and measure the
amount of fixation disparity Associated phoria is the amount of prism
needed to eliminate the fixation disparity Y-axis is the amount of fixation disparity X-axis is the amount of prism
![Page 17: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/17.jpg)
Effect of Prism on FD
Base In prism Base Out prism Vergence movement
![Page 18: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/18.jpg)
Types of fixation disparity curves
Type I Type II Type III Type IV
![Page 19: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/19.jpg)
Type I
![Page 20: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/20.jpg)
Type II
![Page 21: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/21.jpg)
Type III
![Page 22: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/22.jpg)
Type IV
![Page 23: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/23.jpg)
![Page 24: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/24.jpg)
What do the curves tell us?
Measure of vergence adaptation Fast or disparity vergence system Slow or vergence adaptation system
![Page 25: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/25.jpg)
Vertical fixation disparity
Very little adaptation in this system
![Page 26: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/26.jpg)
Spherical lenses
Moves curve up and down
![Page 27: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/27.jpg)
Calculating AC/A ratio
For each lens power find the corresponding prism power that produces the same fixation disparity value
Plot each lens/prism pair of points
![Page 28: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/28.jpg)
Analysis
Quadrant 1 Quadrant 2 Quadrant 3 Quadrant 4
![Page 29: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/29.jpg)
Characteristics of fixation disparity
Fixation distance
![Page 30: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/30.jpg)
Saladin Vs Wesson Card
Ngan et al OVS (2005) Compared the FD and associated phoria
in adults using the Saladin and Wesson cards
Compared the y-intercept (FD) and x-intercept x-intercept.
![Page 31: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/31.jpg)
Saladin Vs Wesson
Test Y-intercept X-intercept
Saladin Card -0.2 0.4
Wesson Cards -10.2 -2.9
![Page 32: Fixation Disparity. Fixation disparity is a small error in the visual system. Occurs as a result of Panums fusional area Small error-minutes of arc 6.](https://reader035.fdocuments.in/reader035/viewer/2022062404/55175074550346a3338b49b9/html5/thumbnails/32.jpg)
Clinical application
Relationship to symptoms Prism prescriptions Effect of orthoptics