ocular motility

Question 1

what is an agonist

Answer 1

muscle producing the movement

Question 2

what is an antagonist

Answer 2

movement in the direction opposite that produced by the agonist

Question 3

what is a contralateral synergist

Answer 3

muscles that cause the two eyes to move in the same direction
i.e. yoke muscles RMR & LLR

Question 4

what is dextro-version and laevo-version

Answer 4

dextro = conjugate movement of both eyes to the right

laevo= conjugate movement of both eyes to the left

Question 5

what is DEXTRO-ELEVATION and LAEVO-ELEVATION

Answer 5

d = - conjugate movement of both eyes up and to the right

L = - conjugate movement of both eyes up and to the left

Question 6

what is DEXTRO-DEPRESSION and LAEVO-DEPRESSION

Answer 6

D = - conjugate movement of both eyes down and to the right

L= - conjugate movement of both eyes down and to the left

Question 7

what is a hess/lees test

Answer 7

Should be carried out on all patients with Incomitant Strabismus

This is done by Orthoptists in the HES

To provide a baseline in conditions likely to develop defective ocular movement in the course of the disease, for example in Graves’ Orbitopathy

Each small square on the grid subtends 5°, allowing the deviation in the primary position to be calculated, fixing with either eye and compared with the deviation recorded in other gaze positions

Question 8

how to interpret hess chart

Answer 8

Which is the abnormal field? The chart with the small field is the abnormal one/affected eye

Is the field compressed? If compressed, consider mechanical causes

Which muscle is underacting? The greatest negative or inward displacement represents the primary underacting muscle

Which muscle is overacting? The muscle with positive or outward displacement indicates an overaction.

Question 9

what is herrings law

Answer 9

states that when an impulse goes to a muscle, causing it to contract, a simultaneous and equal impulse is sent to its contralateral synergist.

For example, when looking to the right, the right lateral rectus and left medial rectus receive equal innervation to contract and the right medial rectus and left lateral rectus to relax.

This is a binocular law, which aids the maintenance of binocular single vision (BSV).

Question 10

what is sherringtons law

Answer 10

This states that when increased innervation is sent to a muscle to cause it to contract, decreased innervation goes to its direct antagonist, which is therefore relatively relaxed.

For example to look right the lateral rectus of the right eye contracts and the medial rectus of the right eye relaxes.

This finely tuned interplay ensures smooth, accurate movement to take up or maintain fixation.

It is a uniocular law.