Movement of the eye nasally is referred to as adduction.
Movement of the eye temporally is referred to as abduction.
Eye muscles that move the eye in a given direction is referred to as an agonist muscle.
An eye muscle in the same eye that moves the eye in the same direction of the primary agonist muscle is a synergist muscle.
An eye muscle in the same eye that moves the eye in the opposite direction as the primary agonist is known as the antagonist muscle.
Increased innervation to any agonist muscle is accompanied by a decreases in the innervation to its antagonists.
Binocular eye movements are conjugate and disconjugate.
The medial rectus muscle is the primary adductor of the eye.
the lateral rectus muscles is the primary abductor of the eye.
The superior rectus acts as he primary elevator.
The inferior rectus acts as the primary depressor of the eye.
The superior oblique causes nasal rotation and depression of the eye and the inferior oblique causes temporal rotation and elevation of the eye.
Theere are 6 extraocular muscles that control movement of the eye and one muscle that controls eyelid elevation the levator palpebrae muscle
The actions of the muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction.
As a small part of the eye, the fovea, provides sharp vision, the eye must move to follow a target.
Eye movements are precise and rapid.
Although eye muscle movement is under voluntary control, most eye movement is accomplished without conscious effort.
The vestibulo-ocular reflex plays an important role in the involuntary movement of the eye.
Four of the extraocular muscles, the rectus muscle, have their origin in the back of the orbit in fibrous ring called the annulus of Zinn.
The four rectus muscles attach to the front half of the eye.
The medial rectus is the muscle closest to the nose.
The superior and inferior recti pull the eye back and slightly medially.
The posterior medial angle causes the eye to roll with contraction of either the superior rectus or inferior rectus muscles.
The extent of rolling in the recti is less than the oblique, and opposite from it.
The superior oblique muscle originates at the back of the orbit.
The superior oblique muscle courses forward to a rigid, cartilaginous pulley, called the trochlea, on the upper, nasal wall of the orbit.
The superior oblique muscle becomes tendinous about 10mm before it passes through the pulley, turning sharply across the orbit, and inserts on the lateral, posterior part of the globe.
The superior oblique travels posteriorly for the last part of its path, going over the top of the eye.
The superior oblique muscle, when activated, pulls the eye downward and laterally.
Then inferior oblique originates at the lower front of the nasal orbital wall, and inserts on the lateral, posterior part of the globe.
The inferior oblique pulls the eye upward and laterally.
Extraocular muscles are under the influence of a system of extraocular soft tissue muscle pulleys in the orbit.
This extraocular muscle pulley system is fundamental to eye muscle movement.
Diseases of the pulleys can cause strabismus.
The extraocular muscles blood supply occurs mainly by branches of the ophthalmic artery, the lacrimal artery.
Branches of the ophthalmic artery include the ciliary arteries, which branch into the anterior ciliary arteries.
Each rectus muscle receives blood from two anterior ciliary arteries, except for the lateral rectus muscle, which receives blood from only one.
Branches of the infraorbital artery supply the inferior rectus and inferior oblique muscles.
Oculomotor nerve
(N. III) supplies
Superior rectus muscle
Inferior rectus muscle
Medial rectus muscle
Inferior oblique muscle
Levator palpebrae superioris muscle
Trochlear nerve
(N. IV) supplies Superior oblique muscle
Abducens nerve (N. VI)supplies Lateral rectus muscle.
The nuclei or bodies of these nerves are found in the brain stem.
The nuclei of the abducens and oculomotor nerves are connected, allowing the coordination of the motion of the lateral rectus in one eye and the medial action on the other.
Two antagonistic muscles, like the lateral and medial recti, contraction of one leads to inhibition of the other.
Muscles have a small degrees of constant activity that keeps the muscles taut: this activity is brought on by discharges of the motor nerve to the muscle.
Intermediate directions of the eye are controlled by the simultaneous actions of multiple muscles: as one eyes shifts the gaze horizontally, one eye will move laterally and the other moves mediall.
Eye movements may be neurally coordinated by the central nervous system, to make the eyes move together and almost involuntarily.
In strabismus, the inability of the eyes to be directed to one point.
There are two main kinds of eye movement:
conjugate movement- the eyes move in the same direction
disjunctive movement-eyes moving in opposite directions.
Conjugate movement is typical when shifting gaze right or left,
Disjunctive is convergence of the two eyes to an object.
Disjunction can be performed voluntarily.
Disjunction is usually triggered by the nearness of a target object.
Clinical examination of the extraoccular eye muscles: examining the movement of the globe of the eye through the six cardinal eye movements.
Turning the eye temporally and horizontally, the function of the lateral rectus muscle is tested.
Turning the eyes nasally and horizontally, the function of the medial rectus muscle is being tested.
When turning the eye down and in, the inferior rectus is tested.
When turning the eye up and in the superior rectus is contracting.
Turning the eye up and out uses the inferior oblique muscle, and turning it down and out uses the superior oblique.
The six movements are tested by drawing a large H in the air with a finger or other object in front of a patient’s face and having them follow the tip of the finger or object with their eyes without moving their head.
Focusing an object as it is moved in toward their face in the midline will test convergence, or the ability for the eyes to turn inward simultaneously to focus on a near object.
Weakness or imbalance of the muscles of the eye can be demonstrated with a penlight shone directly on the corneas.
Normal results of the corneal light reflex is when the penlight’s reflection is located in the centre of both corneas, equally.