Ocular movements:  

 

Dr. Kanthamani,   

Neuro- ophthalmologist, Apollo Hospitals,  Chennai , India.

The purpose of ocular Movements is: 

·To fixate or view objects of interest, with macula.

·To maintain fixation on a moving object. 

·To compensate for the movement of our own bodies, (to maintain an undistorted image).

In our day to day life, the two eyes in their every movement have to move in unison so that binocular vision is attained. It is thus obvious that their motility and co-ordination are sub- served by an accurate and responsive neuromuscular apparatus. 

We shall first study the extra-ocular muscles and then their central nervous control.  

Posterior view of the left eye-

                             

  Thus, the six extra-ocular muscles and their respective actions are:

·        Medial rectus -adduction

·        Lateral rectus -abduction

·        Superior rectus-elevation, adduction, & intortion

·        Inferior rectus-depression, adduction, & extortion

·        Superior oblique –depression, abduction, & intortion

·        Inferior oblique-elevation, abduction, & extortion

The vertical recti and the oblique muscles are also called cyclo-vertical muscles.

Both Superior cyclovertical muscles are Intorters [mnemonic-SIN] and  inferior cyclovertical muscles are extorters,

but their  vertical actions are opposite; the superior oblique is a depressor and the inferior oblique is an elevator.

The RAD  mnemonic is useful to recollect that Recti are ADductors but best efficient and  tested in abducted position &

it is vice-versa for the oblique muscles.

The intra ocular muscles are :

Sphincter pupillae-causes pupillary constriction

Dilater pupillae - causes pupillary dilation

Ciliary muscle-results in accomodation. 

The lids are  opened by the levator palpebrae superiori and  closed by the orbicularis oculi. 

The ocular movements are of four types: 

· Ductions

· Versions

· Vergences

· Supra nuclear movements

 Ductions  refer to the  movement of the one eye, and consist of :

 

 

 

 

      Rt. eye   Abduction

             Adduction

           Elevation

           Depression

      Intorsion [rotation of the eyeball towards the nose around the antero- posterior axis] and

      Extorsion [rotation of the eyeball away from the nose around the antero- posterior axis] 

                               

Versions are binocular movements, in which the two eyes move synchronously and symmetrically in the same direction. The movements are:

Six Positions of Cardinal Gaze:

              

 

           

    DextroElevation-Right&Up gaze

 

        LaevoElevation- Lt & Up gaze

  Rt. Sup.Rectus & Lt. Inf. Oblique

 

    Rt. Inf. Oblique & Lt. Sup. Rectus.

         

           

            

      Dextroversion- Right  gaze

                 PRIMARY GAZE

       LaevoVersion   -    Lt. Gaze  

  Rt. Lat. Rectus & Lt. Med. Rectus

 

     Rt. Med. Rectus & Lt. Lat. Rectus

         

 

           

 DextroDepression- Rt.& down gaze

 

   LaevoDepression-Lt & Down Gaze

    Rt. inf. Rectus & Lt. Sup. oblique

    Rt. Sup. Oblique & Lt. Inf. Rectus

 

           

To test the eye movements,

Use a torch (accommodative target not required), this allows you to view the corneal reflections.

Hold target between 33 to 50 cm away.

Move target slowly in an arc.

Observe eyes and confirm any abnormality by performing a cover test.

There is no set order, however many practitioners perform horizontal versions, then vertical, then diagonals.

Vergences are binocular movements, in which the two eyes move synchronously and symmetrically in the opposite directions. They are : Convergence and Divergence

Supra nuclear movements:

Saccadic systems: 

The function of saccadic movements is to place the object of interest on the fovea rapidly or to move the eyes from one object to another. This can be done voluntarily or it can occur as a reflex triggered by the presence of an object in the peripheral visual field.. They are fast (400-700 o/sec),

The pathway originates in the premotor cortex of the frontal motor area. From there, fibres pass to the contralateral horizontal gaze centre in the pontine paramedian reticular formation (PPRF). 

The right frontal lobe controls saccades to the left and the left frontal lobe those to the right. Irritating lesions may therefore cause a deviation of the eyes to the opposite side.

Smooth pursuit movements :

This generates smooth tracking movements to maintain foveal fixation when viewing a moving object. . The stimulus is movement of the object near the fovea.  These are slow, generally less than 40o/sec.

The pathway originates in the peristriate cortex of the occipital motor area. The fibres then descend and terminate in the ipsilateral horizontal gaze centre in the PPRF. The right occipital lobe therefore controls pursuits to the right and the left occiptal lobe controls  those to the left.

Control of saccadic and pursuit movements is at both the cerebral and brain-stem levels.

Gaze palsies caused by supranuclear disturbances are characterized by the absence of diplopia and  normal vestibulo-ocular reflexes.

Optokinetic nystagmus: 

This is a combination of following (smooth pursuit)movements and rapid re-fixation movements.  This produces optokinetic nystagmus and occurs when a moving, repeating field is presented before the eyes. Optokinetic nystagmus, elicited either by a striped tape or a rotating drum running horizontally or vertically, reacts similarly; absence of the fast phase characterizes lesions of the fronto-pontine tract, of the slow phase the occipito-pontine tract.

Vestibulo–Ocular/Non-Optical movements: 

This produces slow movements in response to head movement or gravity; an equal and opposite eye movement is generated. Their  function is to maintain eye position with respect to any changes of the head and body as a whole for obtaining clear image.. This reflex is present without a visual stimulus. e.g.,vestibular nystagmus (as  in caloric test), Doll’s eye manoeuvre. The pathway originates in the labyrinths and proprioceptors in the neck muscles which derive information concerning head and neck movements. Afferent fibres synapse in the vestibular nucleus and pass to the horizontal gaze centre in the PPRF.

The doll’s head phenomenon( the porprioceptive / oculo-cephalic-reflex) . Rotation of the head in the horizontal plane to one side produces tonic ocular deviation to the opposite side; depression of the chin produces upward deviation to the eyes and elevation of the chin results in downward deviation of the eyes. This test is of importance in the unconscious patient or when voluntary or pursuit movements are impaired; full rotations indicate an intact brain-stem, ocular motor nuclei and efferent motor nerves. 

[Caloric vestibular nystagmus is the most convenient test to elucidate the condition of the vestibular apparatus.Cold water (300C) introduced into one ear evokes nystagmus with the fast phase towards the opposite side, warm water (440C) to the same side and bilateral stimulation produces vertical nystagmus; cold water produces downward deviation with the fast phase. In the unconscious patient the fast phase is usually absent so that a tonic deviation towards the side of the slow phase occurs; the same result marks a lesion in the fronto-pontine pathway, while in the presence of severe pontine damage no result is obtained.] .

Brainstem control: 

Horizontal eye movements are generated from the horizontal gaze centre in the PPRF. From here the output is to the ipsilateral sixth nerve nucleus to abduct the ipsilateral eye. To adduct the contralateral eye, fibres from the PPRF also cross the pons and pass up the medial longitudinal fasciculus (MLF) to the contralateral medial rectus nucleus in the third nerve complex, which also receives independent descending input from the vergence control centres.natomical pathway of medial longitudinal bundle. 

Stimulation of the PPRF on one side therefore causes a conjugate movement of the eyes to the same side. Loss of normal horizontal eye movements occurs when the PPRF is disrupted as follows.

1.       Lesions of the PPRF give rise to ipsilateral horizontal gaze palsies, sparing the vestibulo-ocular reflex.

2.       Lesions of the MLF are responsible for the clinical syndrome of internuclear ophthalmoplegia (INO), characterized by defective adduction of the ipsilateral eye and ataxic nystagmus of the contralateral abducting eye.Convergence of the two eyes is usually normal.

3.       Lesions affecting both the PPRF  and the MLF on the same side give rise to the ‘one-and-a-half syndrome’, characterized by loss of horizontal movement of the ipsilateral eye and no adduction of the contralateral eye.

Vertical eye movements:

Vertical eye movements are generated from the vertical gaze centre known as the rostral interstitial nucleus of the MLF which lies in the mid-brain just posterior to the red nucleus. From each vertical gaze centre, impulses pass to the subnuclei of the eye muscles controlling vertical gaze in both eyes. Cells mediating upward and downward eye movements are intermingled in the vertical gaze centre, although selective paralysis of up-gaze may occur in spite of this.

Up-gaze palsy is typically caused by lesions involving the posterior commissure and characteristically occurs in Parinaud’s dorsal mid-brain syndrome.

Down –gaze palsy is less common and occurs when both sides of the mid-brain tegmentum posterior to the red nucleus are damaged. Causes include cerebrovascular disease and Parkinson’s disease. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

from Peer Reviewed Resources only

 

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