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Hess test
1. Sahibzada Hakim Anjum Nadeem
Co-Incharge OTTC, Optician, Refractionist, COAVS
CEO Anjum Eye Care & Optical Company
Optometrist, Al-Khair Eye Hospital Lahore
Co-Incharge OTTC, Optician, Refractionist, COAVS
Email: shanjum92@gmail.com
2. 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 byWalter
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.
4. INTRODUCTION
The Hess-Screen is a metal plate, 95 cm wide and 95
cm high.
It Includes 24 squares, 8 inner and 16 in outer field.
The central filed is of 15 degree while outer field
limited to 30 degree.
Each square on chart indicates 5 degree.
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.
Foveal Projection
8. 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.
9. INTERPRETATION
Size of the fields: A difference in size shows incomitance.The
smaller field indicates the primarily affected eye. Equal size
shows concomitance, suggesting a long-standing deviation or a
non paretic etiology.
Sloping sides of the fields: This shows an ‘A’ or ‘V’ pattern in
which the horizontal deviation becomes relatively more
convergent on elevation or depression respectively.This usually
implies an underlying bilateral defect of ocular motility.
Examination of the smaller field:1.The type of deviation in
primary position indicates primary deviation. 2.The position of
the greatest restriction of the field indicates the position of the
main limitation of movement. 3.The overactions are indicated
by enlargement of the field.
10. Examination of the larger field: 1.The type of
deviation in primary position indicates the
secondary deviation. 2.The position of the
greatest enlargement of the field shows the
main overaction.
Examination of the outer fields: The outer field
must always be plotted and may show a defect
when the central fields appear normal,
particularly where a mechanical defect is
present, or in cases of slight paresis.
11. Hess Chart (Position)
The basic principle of Hess chart is foveal projection
therefore the higher field belongs to the higher eye.
This is opposite of diplopia charting where the higher
image is of the lower eye.
Position of the central dot indicates whether the
deviation is in primary position or not.
12. Hess Chart (size)
The variation in the size of the Hess chart of each eye is due to the
Hering’s law.
Small field belongs to the eye with primary limitation of movement.
Underaction can be seen with the inward movement of the dots
and therefore the whole curve.
Maximum displacement occurs in the direction of the affected
muscle if the patient has presented early before the spread of
comitance.
13. Overaction can be seen by noting the outward
displacement of the dots.
Maximum displacement occurs in the direction of the main
action of the overacting contralateral synergist in the larger
field.
If the inward and outward displacement is less marked,
secondary underactions and overactions are present as a result
of the development of muscle sequelae.
14. Outer field should be examined for small underactions and
overactions which may not be apparent on the inner field.
A narrow field restricted in opposing directions of
movement denotes a mechanical restriction of ocular
movement.
Equal sized field denote either symmetrical limitation of
movement in both eyes or a non paralytic strabismus
15. Hess Chart (Shape and Measurements)
Each small square on the grid subtends 5 degree at the working
distance of 50 cm.
Therefore the amount of deviation can becalculated.
In primary position, the amount could be calculated by fixing either eye by
the displacement of the pointer from thecentre dots.
The amount of underaction and overaction can becalculated in the various
positions and hence the amount of excursions can also be calculated.
16. USES OF HESSTEST
•Diagnosis of:
Under action or Over action of EOM (which muscle
is affected, degree of paresis).
Extent of development of muscle sequelae.
Mechanical or Neurogenic palsy.
Congenital/Long standing or Acquired palsy.
A orV pattern
Measurement of Deviation (each little square is 5o)
•Planning of surgery (which muscle to operate on)
and post-op effects of surgery
•Monitoring of condition
18. The left chart is much smaller than the right.
Left exotropia – note that the fixation spots in the inner charts of
both eyes are deviated laterally.
The deviation is greater on the right chart (when the left eye is
fixating), indicating that secondary deviation exceeds the
primary, typical of a paretic squint.
Left chart shows underaction of all muscles except the lateral
rectus.
19. Right chart shows overaction of all muscles except
the medial rectus and inferior rectus, the ‘yokes’ of the
sparedmuscles.
The primary angle of deviation (fixing right eye – FR) in
the primary position is −20°
The secondary angle (fixing left eye – FL) is −28°
20. •Right chart is smaller than the left.
•Right chart shows underaction of the superior oblique and
overaction of the inferior oblique.
•Left chart shows overaction of the inferior rectus and
underaction (inhibitional palsy) of the superior rectus.
•The primary deviation (FL) is R/L 8°; the secondary deviation FR
is R/L 17°.
21. • No difference in overall chartsize
• Primary and secondary deviation R/L4°.
• Right hypertropia – note that the fixation spot of the right inner chartis
deviated upwards and the left is deviateddownwards.
• Hypertropia increases on laevoversion and reducesondextroversion
•Right chart shows underaction of the superior oblique andoveraction of
the inferior oblique.
• Left chart shows overaction of the inferior rectus andunderaction
(inhibitional palsy) of the superior rectus.
22. • Right chart is smaller than theleft.
• Right esotropia – note that the fixation spot of the right inner chartis
deviated nasally.
•Right chart shows marked underaction of the lateral rectus andslight
overaction of the medial rectus.
• Left chart shows marked overaction of the medialrectus.
• The primary angle FL is +15° and the secondary angle FR+20°.
• Inhibitional palsy of the left lateral rectus has not yetdeveloped.
23. a. Which is the abnormal eye?
b. Which muscle is underacting?
c. Which muscle is overacting?
d. Is this a long-standing palsy?
e. What is the diagnosis?
24. a. Which is the abnormal eye?
b. Which muscle is underacting?
c. Which muscle is overacting?
d. What is the diagnosis?
25. a. Which muscle is underacting?
b. Which muscle is overacting?
c. What is the diagnosis?
