Hess charting

• Subjective assessment of deviation – Diplopia principal: one target, dissosiation

achieved with different colour glases – Haploscopic principal: two target,one target

pointed and pt has to superimpose it with other.

• Herings law of equal innervation: an equal and simultaneous innervation flows from the brain to pair of muscles of both eyes (yoke muscle) which contract simultaneously in different binocular movements.

• Sherrington's law of reciprocal innervation states that: When a muscle contracts, its direct antagonist relaxes to an equal extent allowing smooth movement.

• Walter Hess, 1908.

• Principle is haploscopic.

• Chart is plotted based on the Hering’s and Sherrington’s law of innervation.

• Dissociation of two eyes is by the means of colors

Prerequisites• Patient should have the following:– Full understanding about what he is supposed to do,

since the test is purely subjective.

– Good vision in both eyes.

– Central fixation.

– Normal retinal correspondence

• Test is performed with each eye fixating in turn. • It is done at 50 cms. • 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.

Method

• Compression of space between the two plotted fixation points indicates underaction of a muscle acting in that direction.

• Expansion indicates overaction.

• Smaller field belongs to eye with paretic muscle.

• Unaffected eye shows larger field expressing the overaction of the contralateral synergist.

Interpretation

• Fields of similar shape and size seen in comitant deviation, while dissimilar shape and size indicate incomitance.

Underaction : Rt lateral rectus

Overaction : Lt medial rectus