Randomized Small Fixation Disparity Polarized Target (Vision Assessment Corporation)
This test was developed by Dr. Paul Lederer as part of the BASS-PL Binocular Accommodative Saccadic Series.1,2
Visual stress while reading is often encountered immediately and long after a concussion. Dr. Lederer created a sensitive way to detect the presence of oculomotor dysfunction when making saccades similar to those made during reading. Using linear cross-polarized glasses, this test allows the patient to witness the dynamics of their own fixation disparities at near while tracking. The target consists of thirty 20/60 Reduced Snellen-sized, single-digit numbers, each of which is surrounded by a circle and are randomly distributed in rows across a card, which is polarized. The arrangement of the numbers are similar to that found on the King-Devick Test.
Both the number and the circle are visible to both eyes when wearing the polarized glasses, and act as a central fusion lock for both identification and accommodative purposes. Two horizontal and two vertical nonius lines surround each circle forming a “plus sign” and are viewed separately by each eye. On the reverse side of the card is a non-polarized replica of the targets. Wearing polarized glasses, I first have the patient rapidly read aloud the numbers on the non-polarized side of the card as a dry run. No fixation disparity will be observed and the patient symptoms are usually minimal to non-existent.
I then ask them to continue reading off the numbers as I flip the card over to reveal the polarized side. In most cases of concussion, the patient will show an immediate strong response as described above. This hypersensitive reaction is the result of viewing ones’ own anomalous and unstable bifixation pattern and is indicative of a dysfunctional accommodative-vergence mechanism and/or saccadic disconjugacy.
We have found this test to be a valuable way to uncover both afferent visual hypersensitivity and efferent oculomotor dysfunction. It is also a great way to demonstrate to patients and their care-givers how “subtle” oculomotor dysfunctions can severely interfere with efficient reading.
- Lederer P, Keep Your Patients’ Eyes on the Page. Lecture, July 27, 2012 https://www.youtube.com/watch?v=t9mcadzOxEw
- BASS-PL Binocular Accommodative Saccadic Series, Vision Assessment Corp. 2675 Coyle Avenue