The Hess chart is used to diagnose strabismus and monitor patients with incomitant strabismus. It involves presenting red lights in different gaze positions while the patient uses red-green glasses and a pointer to indicate if the lights are aligned. Deviations between the plotted points and template indicate the angle of deviation and can identify paretic or overacting muscles. The Hess chart helps locate muscles affected by palsies or contractures and determine if strabismus is due to a primary palsy or secondary involvement of other muscles.

1. Hess Chart
- Dr. Swathi.N

2. Diplopia
Acquired misalignment of the visual axes - image
falls simultaneously on the fovea of 1 eye and
on a non-foveal point in the other eye.

3. The object that falls on these non-corresponding
points must be outside Panum's area to
appear double.

4. Pannum’s area
The region in front and back of the horopter in which single vision is
present - Panum’s fusional area.
In Panum’s area visual objects are seen stereoscopically.

5. Horopter - the locus of all object points that are imaged
on corresponding retinal elements at a given fixation
distance.

6. All object points lying on the horopter curve
stimulate corresponding retinal elements.
By definition, all points on the horopter curve
are seen singly.
Also by definition, all points not lying on the
horopter curve are imaged disparately and,
with certain qualifications, are seen double.
The diplopia elicited by object points off the
horopter is called physiologic diplopia.

7. The same object is seen as having 2 locations in
subjective space, and the foveal image is
always clearer than the nonfoveal image of
the nonfixating eye.

8. The perception of diplopia depends on
• the age at onset,
• its duration,
• the patient's subjective awareness of it.
The younger the child, the greater the ability to
suppress, or inhibit, the nonfoveal image.

9. Diplopia test
Determines the subjective
localization of
a single object point
imaged on the fovea of
the fixating eye
and an extrafoveal retinal
area in the other eye
No horizontal phoria
Esophoria
Exophoria
RE LE

10. The two visual fields must be differentiated

11. Haploscopic Tests
• Two test objects rather than one are
presented to the patient, who is required to
place them in such a fashion that they appear
superimposed.
• Again assuming that correspondence is
normal, the two objects are placed to
stimulate the foveae of the two eyes.

12. • Each eye may be presented with a different target,
• complementary colors may be placed in the visual
field of the patient,
• each eye may be provided with a corresponding
colored filter.

13. Hess Chart
• Contains a tangent pattern displayed on a dark grey background
• Red lights individually illuminatedby a control panel indicate cardinal
positions -
Central field (15° from primary position)
Peripheral field (30°);
Each square represents 5°.
• Eyes dissociated by red -green goggles , red lens in front of fixating eye.
• Red lights illuminated at selected positions; patient holds green pointer,
is asked to superimpose a green light over each red light.
• In orthophoria - two lights should superimposed in all positions of gaze.
• The goggles are then reversed and the procedure repeated.

14. • Diagnosing possible paretic or paralytic conditions in
patients with normal correspondence
• Diagnosis and monitoring of a patient with
incomitant strabismus
• Mechanical or myopathic limitation
• Very useful in the assessment of incomitant squint
• Torsion cannot be detected.

15. • The smaller chart indicates the eye with the paretic
muscle.
• The larger chart indicates the eye with the overacting
yoke muscle.
• The smaller chart will show its greatest restriction in the
main direction of action of the paretic muscle.
• The larger chart will show its greatest expansion in the
main direction of action of the yoke muscle .
• The degree of disparity between the plotted point and the
template in any position of gaze gives an estimate of the
angle of deviation.

16. Red before RERed before LE
Rt LR palsy

17. Red before LE Red before RE
Rt SR palsy

18. Red before LE Red before RE
? Lt SO palsy / Rt IR contracture

19. Red before LE Red before RE
Spread of commitance:
•Rt SR palsy
•Lt IO overaction
•Rt IR contracture
•Lt SO inhibitional palsy
? Primary palsy Lt SO

20. Thank You