HESS EOM - EXTRA OCULAR MUSCLE FUNCTION TEST PAGE 1/2
|Digital Visual Acuity Chart Screening Software|
This test is used to measure Extra Ocular Muscle ( EOM ) function and detect any binocular anomalies
within the visual system.
There are two main laws that govern eye movements, namely;
● Herring's Law of Equal innervation
● Sherrington's law of Reciprocal innervation
Extra Ocular Muscle Function - Set Up & Getting Started
HESS EOM Test
There are two types of Binocular eye movements:
This relates to all 'version' movements of the eyes where both eyes move in the same direction.
- Left ( Laevoversion )
- Right ( Dextroversion )
- Up ( Supraversion )
- Down ( Infraversion )
On first load you shall be required to calibrate your monitor and anaglyph settings.
Follow the few simple steps below to ensure test reliability and EOM deviation results accuracy:
1. Select the Options from the HESS top toolbar
2. Click Screen Calibration and enter the bar width (mm) followed by ‘Save’
3. Select the Anaglyph Calibration from the HESS top toolbar.
It might be necessary to adjust the Red / Green settings to achieve neutrality. ( See User Manual )
4. Click Save ( These calibration settings do not need to be repeated )
Getting started with the HESS EOM Test
Nine Positions of Gaze
The nine positions of gaze are tested and displayed in the following order as they appear to the patient:
● Position 1: Top Left
● Position 2: Top Center
● Position 3: Top Right
● Position 4: Middle Left
● Position 5: Centre | primary position
● Position 6: Middle Right
● Position 7: Bottom Left
● Position 8: Bottom Center
● Position 9: Bottom Right
Note: The HESS results indicates the Position of Gaze and EOM responsible
The patient instructions will be displayed each time the HESS test is run.
1. Place your elbow on the table and then place your chin in your hand.
Keep your head still and do not tilt your head.
2. Put on the Red / Green spectacles and be sure that the Red Filter is in front of your Right Eye.
3. Keep your head very still and move only your eyes.
4. Using the mouse, move the small Dot until it is exactly in the middle of the small ring
and - 'Click' the Left mouse button.
5. The ring will now move to a new position. Keeping your head still, continue to align the Red Dot in the
center of the rings, and 'Click' the Left mouse button when the Red Dot is aligned in the centre of the ring.
6. If you can not align the Red Dot because it is at the edge of the screen,
'Click' when it is as close as you can get it
7. If you are unsure of any of the positions you can simply repeat the test.
Tip: If there is any doubt regarding the accuracy of the test or if the patient is not sure about the positions,
the test can simply be repeated. The test will go through all nine positions of gaze for each eye.
On completion of the test, the results will be displayed and the practitioner is able to interpret the results
from the plot, as well as the deviation table for each eye.
● Setting Up the Hess Test
1. Be sure to calibrate your patient display screen size, anaglyph saturation and viewing distance
under 'Options' before starting.
2. During Hess testing it is important to elimate Head tilt and ensure that the patient's head
is central both horizontally and vertically in front of the screen.
3. Dim the ambient light conditions as Dark as possible to avoid the screen borders acting as a binocular lock.
|'When a muscle receives a nervous impulse to contract, an equal impulse|
is received by the antagonist to relax'
How to perform
|'When a nervous impulse is sent to an ocular muscle to contract, an equal impulse|
is sent to the contra-lateral synergist to also contract'
Positions of Gaze
● How to do the Hess Test
1. The Patient moves the mouse to position the Red Dot in the center of the Green Ring and 'Clicks'
the Left mouse button to place it in the target.
2. Nine positions of gaze are tested for each eye and it is not necessary to change anaglyphs as often found
with traditional methods.
3. On completion the results will be graphically displayed, with the associated deviation(s) in a Table Form.
4. Click 'Start' on the Hess Top menubar to begin testing. Should the patient move their head position
during testing it is recommended that the test be redone.
Note: These points are merely a guideline on performing the HESS test on patients.
This relates to all ' Vergence ' movements of the eyes where the eyes move in opposite directions.
- Convergence (turn inwards)
- Divergence (turn outwards)
The practitioner also needs to establish whether the deviation is constant with the Direction of Gaze ( concomitant ),
or if the deviation varies with the Direction of Gaze ( incomitant ).
Incommitant deviations are less common and are usually of sudden onset, either physical or neurogenic.
It is important to identify recent incommitancies as if no recent trauma has been reported this may require urgent
neurological evaluation. Possible aneurysm, tumor, or hemorrhages need to be investigated.
|Next Page with two examples|
where Herrings Law applies
|Digital Optometry Software - Save Time|