Hess Test Indication &

Interpretation

Siraj SafiLecturer in Optometry PICO

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.

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

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.

Equipment

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.

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.

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.

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

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

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.

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.

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

There may be incomitance in different direction of gaze

• Horizontally• Vertically• Obliquely

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.

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.

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

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.

Is there an A or V pattern?

• Look at the separation of the inner field in up and down gaze.

Some plotted Hess charts

Hess chart

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

Right 3rd nerve palsy.

Lt orbital fracture.

Rt 6th nerve palsy.

Lt SO palsy.

Rt Brown syndrome.

Thankyou