The Hess screen test is used to evaluate eye muscle function and diagnose abnormalities. It involves the patient fixating on lights illuminated on a screen while wearing colored lenses over each eye. Patterns in how the lights are seen can reveal underaction or overaction of extraocular muscles, and determine if a deviation is comitant or incomitant. The test allows diagnosis of conditions like neurogenic or mechanical palsies, and helps evaluate their effects over time and before/after surgery. Interpretation involves analyzing features like the size and direction of any deviation, whether fields are similar between eyes, and if patterns indicate particular affected muscles or nerves.

1. Hess Test Indication
&
Interpretation
Siraj Safi
Lecturer in Optometry PICO

2. Hess Test
• An investigation of binocular vision can be
incorporated into an investigation of the motor
system and an investigation of the sensory system.
• During investigation of the motor system abnormal
position and abnormal movement should be
diagnosed and measured.

3. The Hess screen test was designed by
Walter Rudolf Hess in 1908.
He was a famous neurophysiologist who
was awarded the Nobel Prize in 1949.
The original test used a black screen on
which was marked a square-meter tangent
scale.
Hess screen

4.  The Hess-Screen is a metal plate, 95 cm wide and 95
cm high.
 Includes 24 squares, 12 inner and 12 in outer field.
 The central filed is of 15 degree while outer field
limited to 30 degree.
 Each square on chart indicates 5 degree.

6. Equipment

7. General Principle
 Principle is haploscopic.
 Chart is plotted based on the Herring's and
Sherrington’s law of innervations.
 Dissociation of two eyes by means of colors.

8. Requirements
 Full understanding about what he is supposed to
do, since the test is purely subjective.
 Good vision in both eyes.
 Foveal projection in the presence of normal retinal
correspondence.

9. Method
 Test is performed with each eye fixating in
turn.
 It is done at 50 cm.
 Patient wears red and green glasses.
 Eye to be tested should have green glass
in front of it.
 The chart has electronically operated
board
with small red lights.
 Patient is asked to place green light in
each of points on red light as illuminated.
 Next the goggles are changed.

10. o Compression of space between the two plotted fixation points
indicates underaction of a muscle acting in that direction.
o Expansion indicates overaction.
o Smaller field belongs to eye with paretic muscle.
o Unaffected eye shows larger field expressing the overaction of
the contralateral synergist.
o Fields of similar shape and size seen in comitant deviation,
while dissimilar shape and size indicate incomitance.
Interpretation

11.  Diagnosis of:
 Under action or Over action of EOM.
 Mechanical or Neurogenic palsy.
 Congenital/Long standing or Acquired pals.
 A or V pattern
 Planning of surgery and post-op effects of surgery
 Monitoring of condition.
Uses of Hess Test

12. Some Important Questions
 What is the direction of deviation i.e. Eso, Exo,
Hyper, Hypo?
 Look at the position of the central spot as the
patient indicated.
 There may be a combined horizontal and vertical
deviation.

13.  What is the size of deviation?
 Each square on the Hess chart represent 5 degree
of deviation.
 Look at the position of the central target and
estimate the deviation.

14. 3. Is the deviation concomitant or
Incomitant?
Look at the position of corresponding target in each eye
• Is the deviation same in:
a. Each eye
b. Each direction of gaze
• There may be Incomitance in primary position with each eye,
indicate:
A recent palsy
A long standing palsy controlled by AHP
A mechanical etiology

15. There may be incomitance in different direction
of gaze
• Horizontally
• Vertically
• Obliquely

16. Is there a smaller field?
• The eye with the smaller field or range of
motility is usually the affected eye .
• Either due to neurogenic or mechanical
etiology.

17. Which is the affected muscle or
nerve?
• The position of gaze with the largest under
achieved eye movement is associated with
the affected muscle or the nerve supplied.

18. Has the muscle sequelae spread to
produce concomitance?
• Look for the four stages in muscle sequelae.
• Muscle sequelae spreads instantly to stage
1&2 but may take several months to spread
to stage 3&4

19. Is the etiology mechanical or
Neurogenic?
Mechanical aetiology have characteristic
feature:
– Straight lines indicating sudden limitation of movement
e.g. Upgaze in blowout fracture.
– “Laurel and Hardy” field e.g. in Blow out fractures.
– “Dog --ear” in e.g. Brown syndrome.

20. Is there an A or V pattern?
• Look at the separation of the inner field in
up and down gaze.

21. Some plotted Hess charts

22. Hess chart

23. Duane's retraction syndrome of type A more
limited abduction than Adduction.

24. Right 3rd nerve palsy.

25. Lt orbital fracture.

26. Rt 6th nerve palsy.

27. Lt SO palsy.

28. Rt Brown syndrome.

29. Thankyou