Calibration Procedures

15 February 2022
10 - 30 mins
Reading

Eye calibrations

If you have not previously calibrated your eyes you must do that first. The eyes should be calibrated anytime you change the goggle/camera, or the goggles are moved on the patient’s face.

Both VNG and vHIT use a 5 dot pattern for calibrations. For VNG you must use the TV/monitor screen to generate the fixation points and for ESC vHIT it is recommended that you always use the attached laser to generate the fixation points. The software screen will be the same regardless of which stimuli source is used.

 

VNG eye calibrations

For VNG calibrations the patient is instructed to look straight ahead and keep their head still and following the moving targets with their eyes only. The VNG calibration process is automated so as soon as the patient has correctly fixated an individual point the dot will automatically move to the next fixation point.

At the beginning of testing, the calibration button will be highlighted in white to prompt you to begin a calibration before moving on to other testing.

Menu, including burger menu icon, home icon, up arrow, cog, start button, and calibration button. 30s in a large font size in the middle of the menu.

Figure 1 Begin calibration

When you are in the calibration screen you will see there are many different things you can do here. From the Advanced Setting button, you adjust the patient’s distance to the target if that has changed and you can change the stimulus size if the patient has visual problems seeing the dot. Here you can also choose the default calibration if for any reason the patient cannot complete the calibration task. Using the Target Center button on the side allows you change the alignment of the center dot on the TV screen. This can be helpful with very tall patients.

Calibration screen with no eye positions completed. Options to the left include start calibration, use default calibration, distance to patient, and target size. The selected source is top mount camera. The selected stimulus is TV.

Figure 2 Calibration Screen options

Using the tool bar just above the eyes you can center the eyes (if you have a top mount goggle), you can adjust the tracking thresholds, change your default eye tracker and disable either eye if necessary.

Drop down list with eye tracking options, including curve tracker, ipm tracker, and convex hull tracker.

Figure 3 Calibration drop down menu for eye tracker selection

From the drop menus you can change the input source and the stimuli source.

Drop down list with source options, including top mount camera, eyeseecam, and vorteq second gen.

Figure 4 Calibration drop menu for input and stimuli sources

Once you have made any necessary changes to any of the settings, then you can press start to begin the calibration procedure.

Calibration options, including start calibration, use default calibration, and advanced settings.

Figure 5 Start Calibration button

The patient is instructed to look at each of the five targets. The large solid yellow dot represents the current target position. As they look at each target a yellow check mark will appear. If the calibration values are within acceptable ranges after calibration is completed the yellow check marks will turn green and if they are outside of acceptable ranges, the check marks will turn red. If the patient is not able to fixate an individual target you can manually override it by pressing Accept Point and then the calibration will move on to the next target.

Calibration underway, visible by two yellow check marks for center and left, empty for up and down, and a solid yellow dot for the right position.

Figure 6 Calibration in progress

Once all five targets have appeared you will be given the option to Accept the values and close the calibration screen.

Completed eye calibration, visible by five green checkmarks in the up, left, down, right, and center positions. Three options are available to the left: accept and close, redo all, and use default and close.

Figure 7 Calibration completed and within normal limits

If some of the values are not acceptable you can choose to repeat the calibrations. You can repeat the horizontal, vertical or all of the points. You can choose the Table option to see more detail on the numeric values which could help in troubleshooting.

Failed vertical calibrations, visible by a red X in the up, center, and down positions.

Figure 8 Failed vertical calibrations with the option to redo them

And lastly, if you want to adjust the data points you can manually move the analysis region to a cluster you feel is a better representation of the patient’s eye movements by clicking on the red circle and moving it to the acceptable spot. Of course, you can always reset the changes back to the original default.

Graph representation of the eye calibration. Red circles are placed by the software in the left, up, right, and down positions for where it has detected a cluster of eye positions.

Figure 9 Adjusting the calibration clusters manually

Once you have completed the calibration and saved the data you can move on to begin the testing. If you choose to come back later and review or print your calibration data, you can do that from test menu.

Figure 10 Review previously completed calibrations and print tracings or delete videos

 

ESC vHIT eye calibrations

EyeSeeCam calibration will follow similar set up steps but since you are using the laser and not the TV you will not have the options to change the target size or position.

Source options, including top mount camera, eyeseecam, and vorteq second gen. Stimulus options, including TV, digital light bar, and eyeseecam laser.

Figure 11 ESC vHIT Calibration Screen

Since laser always present 5 stationary dots you will need to instruct your patient to focus on only one dot at a time. You will start by having them look at the center dot. Then you will hit Accept Point. You will hear a ding sound from the computer. At that time tell the patient to look to the left dot (the next dot is always shown as a bigger yellow dot on the computer screen for you to guide the patient as to which laser dot to look at). Again, hit Accept Point and guide them to the next dot. Repeat this process until they have fixated all 5 laser dots.

ESC vHIT calibration underway, shown in the following sequence: 1) Solid yellow dot in the center position. 2) Accept Point option. 3) Yellow checkmark in the center position, and solid yellow dot in the left position. 4) Accept Point option.

Figure 12 ESC vHIT calibration steps

After all, 5 targets appeared you can Accept and Close the calibration screen or repeat any poor calibration.

 

Head calibrations

The head calibration is only for the EyeSeeCam vHIT with the built in IMU. As the IMU is mounted in the camera housing, the position of the IMU changes each time you position the camera so it will be different for each person and each time you place the goggles on the head.

 

EyeSeeCam vHIT head calibrations

For ESC vHIT the position of the IMU/Camera must also be calibrated when before testing vertical impulses. So, when you begin a LARP or RALP test the calibration button will be highlighted in white again. Select Start Calibration and then select Head Calibration.

Figure 13 Head calibration for ESC vHIT

The guide will help you move the head at the correct speed in the horizontal and vertical planes. Green is the correct speed grey is too slow and red is too fast.

Four identical head calibration graphs, with head velocity in degrees as the sole, x-axis value. Two of the graphs have a green peak, indicating a correct head velocity. One has a red peak, indicating a too fast head velocity. The final is grey, indicating a too slow head velocity.

Figure 14 Head velocities for ESC vHIT head calibration

When you have moved the head at the correct speed in both planes the test will automatically stop and the head calibration results will appear. You can Accept and Close or Redo the calibration. Once you Accept and Close you then begin vertical canal testing.

An almost perfect, perpendicular cross in the vertical and horizontal directions. Options to accept and close or redo calibration.

Figure 15 Completed vHIT head calibration

You can go back and review or print the calibrations from the test screen.

Figure 16 Review or print calibrations

If you need further information on how to perform the VNG or vHIT tests, please refer to the quick guides for those tests of the Additional Information Manual.

 

Troubleshooting

For the eye calibrations, if it fails on range you should check patient distance from the TV. If it fails in symmetry, instruct the patient to only move their eyes to the target while keeping head straight. Also check the tracking to ensure crosshair are staying in the center of pupil during calibration”

Figure 17 Failed calibration table of values

For further information please refer to the Instructions for Use or Additional Information manuals.


Presenter

Michelle Petrak
Michelle Petrak, Ph.D., is the Director of Clinical Audiology and Vestibular Research for Interacoustics. Her primary role is development and clinical validation of new technologies in the vestibular and balance areas. She is located in Chicago where she is a licensed private practice clinical audiologist at Northwest Speech and Hearing (NWSPH). Dr. Petrak received her doctorates in Electrophysiology (1992) and Biomolecular Electronics (1994) from Wayne State University and her Masters in Audiology in 1989. Her special areas of expertise include vestibular and balance assessments and management of the dizzy patient. Dr. Petrak is involved with new innovative product developments, clinical evaluations of new protocols, and publishing, teaching, and training on the management of patients with dizziness. She continues to lecture extensively nationally and internationally, and she has numerous articles published in the hearing industry journals. She also participates on the committees for several doctoral students as support for the research projects.

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