
<ul>
  <li>Eye movements are paired even when they move in different directions</li>
  <li>Levels of neural control</li>
  <ul>
    <li>Reflex, subcortical level</li>
    <li>Cortical control:</li>
    <ul>
      <li>
        Frontal cortex: voluntary activity (frontal eye field are connected to the extraocular
        nuclei via the paramedian pontine reticular formation)
      </li>
      <li>Occipital cortex and superior colliculus: coordinating centres</li>
    </ul>
    <li>Interneuronal connections:</li>
    <ul>
      <li>Paramedian pontine reticular formation</li>
      <li>Vestibulo-ocular and cervico-ocular reflexes</li>
    </ul>
  </ul>
</ul>
<ul>
  <li>
    Occur around three axes passing through the centre of rotation at right angles to each other
    (Fick&rsquo;s axes)
  </li>
  <ul>
    <li>2 horizontal axes of Fick (X and Y) and a vertical Z axis</li>
    <li>Secondary gaze positions are achieved by rotation around the X or Z axes</li>
    <li>
      Tertiary gaze (ie. oblique) positions are achieved by rotation around both X and Z axes
      simultaneously
    </li>
    <li>Torsional movements occur around the Y axis</li>
  </ul>
</ul>
<ul>
  <li>
    Centre of rotation is 13.5/14mm behind corneal apex and 1.6mm nasal side to the geometric centre
  </li>
  <li>
    Near-fixation is approximately 0.33m in front of the eyes and requires convergence and
    accommodation
  </li>
  <li>
    Primary position of gaze: position taken up by both eyes fixating on a distant object directly
    ahead
  </li>
  <li>
    Secondary positions: any other positions such as near-fixation, cardinal positions, midline
    vertical positions etc.
  </li>
</ul>

## Binocular movements
<ul>
  <li>
    Isolated agonist model: primary action of muscles occurs when the muscle contracts in the
    primary position
  </li>
  <li>
    Versional (conjugate) movements: the eyes move in the same direction and the axes remain
    parallel.&nbsp;
  </li>
  <ul>
    <li>Controlled by pairs of muscles</li>
    <li>Main types of conjugate eye movements</li>
    <ul>
      <li>Saccades (supranuclear control): align the fovea with the target</li>
      <li>
        Smooth pursuit (supranuclear control): maintain fixation once the saccadic system has found
        the target
      </li>
      <li>
        Non-optical reflex movements: maintain eye positions without conscious input as body/head
        position changes
      </li>
    </ul>
  </ul>
</ul>
<ClinicalCorrelate>
  <p>
    Disturbance of supranuclear eye movement function leads to gaze palsies (further explored in
    Part 2 package)
  </p>
</ClinicalCorrelate>
<ul>
  <li>
    Vergence (disjunctive) movements: simultaneous movement in opposite directions (eg. convergence)
  </li>
  <ul>
    <li>Slower than versional movements</li>
    <li>Stimulated by retinal disparity</li>
  </ul>
</ul>
<ClinicalCorrelate>
  <p>Transection of the corpus callosum inhibits vergence movements.</p>
</ClinicalCorrelate>
<ul>
  <li>In the fusion-free position of physiological rest, the eyes are slightly divergent</li>
  <li>
    Amplitude of convergence: the difference between the converging power for near and far points of
    convergence
  </li>
</ul>
<HotTopic>
  <>
    <p>Hering&rsquo;s law.&nbsp;</p>
    <ul>
      <li>
        During voluntary movements of the eye, equal and simultaneous innervation occurs from the
        CNS to the muscles of both eyes allowing gaze in a particular direction ie. the extent of
        movement of one eye is equal and symmetrical to the other
      </li>
      <li>Applies to all voluntary conjugate movements</li>
    </ul>
  </>
</HotTopic>
<ul>
  <li>
    Sherrington&rsquo;s law of reciprocal innervation: increased contraction of the prime mover EOM
    is associated with diminished contractile activity of the antagonist muscle
  </li>
</ul>
<HotTopic>
  <>
    <p>Primary, secondary and tertiary actions of the EOMs</p>
    <div>
      <table>
        <tbody>
          <tr>
            <td>
              <span className="font-semibold">Muscle</span>
            </td>
            <td>
              <span className="font-semibold">Primary</span>
            </td>
            <td>
              <span className="font-semibold">Secondary</span>
            </td>
            <td>
              <span className="font-semibold">Tertiary</span>
            </td>
            <td>
              <span className="font-semibold">Yoke (contralateral eye)</span>
            </td>
            <td>&nbsp;</td>
          </tr>
          <tr>
            <td>Medial rectus</td>
            <td>Adduction</td>
            <td>nil</td>
            <td>nil</td>
            <td>Lateral rectus</td>
            <td>&nbsp;</td>
          </tr>
          <tr>
            <td>Lateral rectus</td>
            <td>Abduction</td>
            <td>nil</td>
            <td>nil</td>
            <td>Medial rectus</td>
            <td>&nbsp;</td>
          </tr>
          <tr>
            <td>Superior rectus</td>
            <td>Elevation(maximal in abduction)</td>
            <td>Intorsion (maximal in adduction)</td>
            <td>Adduction</td>
            <td>Inferior oblique</td>
            <td>Synergists for medial rectus and antagonists for lateral rectus&nbsp;</td>
          </tr>
          <tr>
            <td>Inferior rectus</td>
            <td>Depression (maximal in abduction)</td>
            <td>Extorsion (maximal in adduction)</td>
            <td>Adduction</td>
            <td>Superior oblique</td>
          </tr>
          <tr>
            <td>Superior oblique</td>
            <td>Intorsion</td>
            <td>Depression (in adduction)</td>
            <td>Abduction</td>
            <td>Inferior rectus</td>
            <td>Synergists for lateral rectus and antagonists for medial rectus</td>
          </tr>
          <tr>
            <td>Inferior oblique</td>
            <td>Extorsion&nbsp;</td>
            <td>Elevation (in adduction)</td>
            <td>Abduction</td>
            <td>Superior rectus</td>
          </tr>
        </tbody>
      </table>
    </div>
  </>
</HotTopic>

## Yoked muscles
<ul>
  <li>Contract to move both eyes in the same direction</li>
  <li>Right lateral rectus and left medial rectus both move the eyes to the right</li>
  <li>Right superior oblique and left inferior rectus both move the eyes down and to the left</li>
  <li>Right inferior rectus and left superior oblique both move the eyes down and to the right</li>
</ul>

## Smooth pursuit movements
<ul>
  <li>Smooth, continuous tracking movements</li>
  <li>Keep an object on the fovea</li>
  <ul>
    <li>
      Stimulated by &ldquo;retinal slip&rdquo; ie. the movement of the target across the retina
    </li>
  </ul>
  <li>Velocity of 30-50 degrees/second (beyond this it breaks down)</li>
  <li>Latency of 150ms</li>
  <li>Complex ipsilateral supranuclear control: PPRF, superior colliculi, cerebellum&hellip;</li>
</ul>
<HotTopic className="mb-6">
  <p>
    Note that smooth pursuit supranuclear control is ipsilateral compared to saccadic control which
    is contralateral
  </p>
</HotTopic>
<ClinicalCorrelate>
  <>
    <p>Smooth pursuit movement is lost on the ipsilateral side in occipitoparietal lesions</p>
    <ul>
      <li>Causes asymmetric optokinetic nystagmus (Cogan&rsquo;s law)</li>
    </ul>
  </>
</ClinicalCorrelate>

## Saccadic movements
<ul>
  <li>Short, sharp movements</li>
  <li>Place an object in the peripheral field onto the fovea (rapid relocation of fixation)</li>
  <ul>
    <li>Visual acuity is reduced during saccades</li>
    <li>Associated with selective suppression of motion detection</li>
    <li>Increased visual threshold during the saccade</li>
  </ul>
</ul>
<ul>
  <li>Fastest eye movements: velocity of 800-1000 degrees/second</li>
  <li>Latency of 100ms</li>
  <li>
    Controlled by the contralateral frontal cortex (supranuclear): the premotor frontal eye fields
    (FEF)
  </li>
  <ul>
    <li>
      Impulses for horizontal movement pass to the contralateral paramedian pontine reticular
      formation (PPRF): horizontal gaze centre
    </li>
    <ul>
      <li>Neurones then pass</li>
      <ul>
        <li>Directly to the ipsilateral sixth nerve nucleus</li>
        <li>
          Indirectly via interneurones which cross to the contralateral MLF and to the medial rectus
          subnucleus of the contralateral third nerve
        </li>
      </ul>
    </ul>
    <li>
      Vertical pathways are less well mapped: bilateral mediation via the midbrain vertical gaze
      centre (rostral interstitial nucleus of the MLF)
    </li>
  </ul>
</ul>

## Fixation movements
<ul>
  <li>
    Move the retinal image slightly to prevent image fade due to bleaching of the photoreceptor
    pigments (Troxler&rsquo;s phenomenon)
  </li>
  <li>Drifts occur monocularly</li>
  <li>Microsaccades are binocular and occur with sustained foveal fixation</li>
  <li>Aim for the best perceived image with fresh cones</li>
</ul>

## Visual reflexes
<ul>
  <li>Mediated by the vestibular system&nbsp;</li>
  <ul>
    <li>Sends efferents to the horizontal gaze centre</li>
  </ul>
  <li>Fixation reflex</li>
  <ul>
    <li>Ability to fixate in bright light</li>
    <li>Developed within a few days of birth</li>
    <li>Demonstrated by tests for optokinetic nystagmus</li>
  </ul>
  <li>Oculovestibular reflexes</li>
  <ul>
    <li>Eye movements responding to head/trunk positional changes&nbsp;</li>
    <li>
      Utricle and saccule detect head tilting/gravitational effects: input to the inferior and
      medial vestibular nuclei
    </li>
    <li>
      Semicircular canals detect rotatory movements: input to superior and medial vestibular nuclei
    </li>
    <li>
      Floculonodular lobe of the cerebellum controls vestibular inputs to the oculomotor system
    </li>
    <li>Require intact brainstem function</li>
    <li>Rotational movements of the head demonstrate this reflex (doll&rsquo;s head)</li>
  </ul>
</ul>
<HotTopic>
  <>
    <p>Caloric testing</p>
    <ul>
      <li>
        Stimulation of a semicircular canal leads to nystagmus in the plane of that canal with the
        slow phase occurring in a direction opposite to that causing the nystagmus (the direction of
        the nystagmus is described relative to the fast saccadic part)
      </li>
      <ul>
        <li>
          Warm water causes endolymph to rise and stimulates the semicircular canal (caloric
          testing)
        </li>
        <ul>
          <li>Warm water causes saccadic movement to the ipsilateral side&nbsp;</li>
          <li>Cold water causes saccadic movement to the contralateral side</li>
          <li>Mneumonic: cold opposite, warm same (COWS)</li>
        </ul>
        <li>Bilateral stimulation causes vertical nystagmus</li>
        <li>The response to caloric testing:&nbsp;</li>
        <ul>
          <li>Reduced by: fixation on an object, optokinetic stimulus</li>
          <li>Increased by: scotopic conditions, high plus lenses</li>
        </ul>
      </ul>
    </ul>
  </>
</HotTopic>
<ul>
  <li>Oculocervical reflex</li>
  <ul>
    <li>Proprioceptors in the neck provide information about neck position</li>
    <li>Lateral movements of the head about the vertical axis produces this reflex</li>
  </ul>
</ul>

## Optokinetic nystagmus
<ul>
  <li>Stationary observer and moving scene or vice versa</li>
  <li>Elicited by a striped drum revolving at 30-100 degrees/second</li>
  <li>
    Slow phase (smooth pursuit component) when eye follows target and fast flick (saccadic movement)
    when they relocate to new target position
  </li>
  <li>Requires intact cortex and patient&rsquo;s attention</li>
  <li>Defective response implies cerebral cortex lesion</li>
</ul>
<HotTopic>
  <p>A central scotoma increases the frequency of optokinetic nystagmus&nbsp;</p>
</HotTopic>

## Downbeat nystagmus
<ul>
  <li>Usually indicative of cervicomedullary structural disease</li>
  <li>Causes:</li>
  <ul>
    <li>Arnold-chiari malformation</li>
    <li>Stroke</li>
    <li>MS</li>
    <li>Platybasia (Paget&rsquo;s disease and Gorlin Goltz syndrome)</li>
  </ul>
</ul>


Physiology

Eye Movements

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance