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