The ocular counter roll test is a clinical test to assess otolith function, which takes advantage of a torsional eye tracking algorithm. The test is done with video recording, so it is referred to as a video Ocular Counter Roll test (vOCR). When the head is tilted, the eyes react with a torsional counter roll. This is a called an ocular counter roll (OCR). It is initiated by the vestibular ocular reflex (VOR).
To perform the test, you should first calibrate the Torsion eye tracker. This allows the algorithm to identify the iris and track the movements of the eyeball.
First select the Ocular Counter roll protocol from the test menu.
Figure 1 – Test Menu
Then select the calibration option.
Figure 2 – Calibration Selection
Once in the calibration menu you can perform 2 tasks:
First calibrate the Torsion tracker. You can use the Auto Detect button to find the appropriate iris area for tracking. If the white tracking circles are not encompassing enough of the iris you can use the manual slider adjust bars to make small adjustments.
Figure 3 – Calibrate Torsion Tracker
When you are satisfied that the tracker is stable around the eyes then use the Set Reference button to finish the calibration.
Figure 4 – Set Torsion Reference
Next, calibrate the eyes to the TV monitor. Instruct the patient to look at each of the five dots. The test will automatically stop when the calibration is completed.
Figure 5 – Video Eye Calibration
Once the system is calibrated you are ready to begin testing. The TV screen will have a solid background and a center fixation dot. Have the patient look at the dot while you rotate their head. The patient can also rotate their head themselves if you prefer. The instructions are too slowly rotate the head towards the left shoulder and hold it there for 10 seconds. During that time the data is being recorded. After 10 seconds press the enter key and then ask the patient to rotate their head towards the right shoulder. This is called a static ocular counter roll test because the patient is holding their head still in each position.
In the results section you will see the torsional nystagmus for clockwise and counterclockwise rotations as the head is tilted to the left and then to the right.
Figure 6 – (a) Ocular Counter Roll test being performed and (b) Graphical display of test results
You can measure the degree of torsion using the edit functions to add in numerical values.
Figure 7 – Using edit functions to add numerical values to the torsion in the ocular counter roll test.
For further assistance, if needed, please refer to the Instructions for Use and Additional Information manuals.