
<ul>
  <li>6 muscles for movements of the globe</li>
  <ul>
    <li>4 recti arising from the tendinous ring</li>
    <li>2 oblique</li>
  </ul>
  <li>1 further muscle for eyelid movement: levator palpebrae superioris</li>
  <li>The collagen tendons of the muscles blend with the scleral collagen</li>
</ul>
<ClinicalCorrelate>
  <>
    <p>Anterior segment ischaemia</p>
    <ul>
      <li>Two muscles can generally be removed safely</li>
      <li>
        However removing four muscles will certainly cause ischaemia of the anterior segment and so
        concern develops when three are removed/operated on
      </li>
    </ul>
  </>
</ClinicalCorrelate>
<h2 id='histology'>Histology</h2>
<ul>
  <li>The EOMs differ from other skeletal muscle</li>
  <li>Much higher ratio of nerve axons to muscle fibres</li>
  <ul>
    <li>1:2 to 1:7 ratio of motor neuron to muscle fibres for very precise control</li>
  </ul>
  <li>Round/oval fibres which are smaller in the periphery and larger centrally</li>
  <li>The muscle sheath (epimysium) is thinner</li>
  <li>
    The muscle fibres are surrounded by more connective tissue (perimysium) so are less tightly
    packed
  </li>
  <li>
    EOMs are among the <strong>most vascularised muscles </strong>in the body second only to the
    myocardium
  </li>
  <li>They are poorly fasciculated</li>
</ul>
<ul>
  <li>All supplied by single motor endplates&nbsp;</li>
  <li>Two types</li>
  <ul>
    <li>
      Fibrillinstruktur: type A thick, fast twitch type supplied by single motor endplates
      (&lsquo;en plaque&rsquo;). These predominate in the outer, orbital zone of the muscles, and
      provide for saccadic movements
    </li>
    <ul>
      <li>Rich in mitochondria</li>
      <li>Well defined myofibrils</li>
      <li>Well developed sarcomeres</li>
    </ul>
    <li>
      Felderstruktur: type B, thin fibres, are innervated by multiple nerve endings (&lsquo;en
      grappe&rsquo;) and predominate in the inner, zone adjacent to the globe; provide for
      slow/tonic, smooth pursuit movements
    </li>
    <ul>
      <li>Produce tonic contraction in response to ACh</li>
      <li>Poorly defined myofibrils and poorly developed sarcoplasmic reticulum</li>
      <li>Zig-zag Z lines</li>
      <li>Grape-like nerve endings</li>
      <li>Less blood supply than fibrillinstruktur fibres</li>
    </ul>
  </ul>
</ul>
<HotTopic>
  <p>There are some histological features that are associated with myopathy but considered normal in
    EOMs</p>
</HotTopic>
<ul>
  <li>Mononuclear cell infiltrate</li>
  <li>Central nuclei</li>
  <li>Disorganised sarcolemma</li>
  <li>Disrupted Z-lines</li>
  <li>Mitochondrial clumping</li>
</ul>
<h2 id='recti-muscles'>Recti muscles</h2>
<ul>
  <li>The superior and inferior recti run at approx 25 degrees to the optical axis</li>
  <li>Their insertions form the spiral of Tillaux</li>
  <li>Superior branch of oculomotor:</li>
  <ul>
    <li>Superior rectus</li>
    <li>Levator</li>
  </ul>
  <li>Inferior branch of oculomotor:</li>
  <ul>
    <li>Medial rectus</li>
    <li>Inferior rectus</li>
  </ul>
  <li>Abducens nerve: lateral rectus</li>
  <Note>
    <p>The lateral rectus has a small second head arising from the greater wing of the sphenoid bone,
      lateral to the annulus of Zinn</p>
  </Note>
</ul>
<HotTopic>
  <p>Table of recti insertions relative to limbus</p>
  <div>
    <table>
      <tbody>
        <tr>
          <td className="font-semibold">
            Distance from insertion to limbus
          </td>
          <td className="font-semibold">
Comment
          </td>
        </tr>
        <tr>
          <td>Medial rectus</td>
          <td>5.5mm (shortest tendon)</td>
          <td>Largest muscle</td>
        </tr>
        <tr>
          <td>Inferior rectus</td>
          <td>6.5mm</td>
          <td>Auxiliary supply from infraorbital artery</td>
        </tr>
        <tr>
          <td>Lateral rectus</td>
          <td>6.9mm (longest tendon)</td>
          <td>
            Only receives one anterior ciliary arteryAuxiliary supply from branch of the lacrimal
            artery
          </td>
        </tr>
        <tr>
          <td>Superior rectus</td>
          <td>7.7mm</td>
          <td>&nbsp;</td>
        </tr>
      </tbody>
    </table>
  </div>
</HotTopic>
<ClinicalCorrelate className="mt-6">
  <p>In developmentally delayed children, muscle surgery for squints should be delayed until much
    later, treating amblyopia first, since early muscle surgery frequently leads to overcorrection.</p>
</ClinicalCorrelate>
<h2 id='oblique-muscles'>Oblique muscles</h2>
<ul>
  <li>Superior oblique arises from the body of the sphenoid, superomedial to optic canal</li>
  <ul>
    <li>Rounded tendon that passes through the trochlea&nbsp;</li>
  </ul>
</ul>
<Note>
  <p>The trochlea is a cartilaginous pulley-like structure on the frontal bone which is the only
    cartilage within the normal orbit</p>
</Note>
<ul>
  <li>
    Pulls at an angle of approximately 55 degrees from the visual axis in the primary position
  </li>
  <li>Only extraocular muscle to have a fusiform (spindle) shape</li>
</ul>
<ul>
  <li>
    Inferior oblique arises from the medial floor of the orbital rim (precisely, from the posterior
    lacrimal crest of the maxilla) but lateral to the nasolacrimal duct
  </li>
  <ul>
    <li>Shortest muscle&nbsp;</li>
    <li>Travels in a posterolaterally direction</li>
    <li>Pulls at an angle of approximately 50 degrees from the visual axis</li>
    <li>Receives additional supply from the infraorbital artery</li>
  </ul>
  <Note>
    <li>Inferior oblique has no tendon</li>
  </Note>
</ul>
<HotTopic>
  <p>Both obliques pass <span className="font-semibold">below </span>their corresponding rectus muscle before inserting
    into the sclera behind the equator of the globe.</p>
</HotTopic>
<p>Nerve supply</p>
<ul>
  <li>Inferior oblique: inferior branch of oculomotor</li>
  <li>Superior oblique: trochlear nerve (enters SOF outside the tendinous ring)</li>
</ul>
<ClinicalCorrelate>
  <>
    <p>The most common cause of both unilateral and bilateral proptosis is thyroid orbitopathy. The
      order of frequency of affected muscles is (from most to least):</p>
    <ol>
      <li>Inferior rectus</li>
      <li>Medial rectus</li>
      <li>Lateral rectus</li>
      <li>Superior rectus</li>
      <li>Obliques&nbsp;</li>
    </ol>
  </>
</ClinicalCorrelate>
<h2 id='relations'>Relations</h2>
<ul>
  <li>Frontal nerve passes above the levator</li>
  <li>Lacrimal nerve passes above lateral rectus</li>
  <li>
    Nasociliary nerve (the continuation of the ophthalmic div.) passes along the superior border of
    medial rectus
  </li>
  <li>Ophthalmic artery travels above medial rectus</li>
  <li>Inferior div. of oculomotor runs above the inferior rectus</li>
  <li>Abducens nerve passes along the medial aspect lateral rectus</li>
  <li>Trochlear nerve runs along the upper surface of the superior oblique</li>
</ul>
<h2 id='oculocardiac-reflex'>Oculocardiac reflex</h2>
<ul>
  <li>Trigemino-vagal:</li>
  <ul>
    <li>
      Afferent limb formed by sensory fibres from the extraocular muscles travelling via the long
      and short ciliary nerves (through the ciliary ganglion but not synapsing), along the
      nasociliary nerve and then the ophthalmic
    </li>
    <li>Efferent limb is formed from the brainstem to the heart via the vagus nerve</li>
  </ul>
  <li>Primarily elicited by traction on the EOMs</li>
  <ul>
    <li>Eg. squint surgery</li>
    <li>Orbital fractures with muscle entrapment</li>
  </ul>
  <li>Can lead to severe bradycardia or even asystole</li>
</ul>


Orbit and ocular adnexae

Extraocular Muscles

Intro

FRCOphth Part 2 Study Notes

Tumours, masses and neoplasia

Tumours overview

Uveitis

Uveitis background

Anterior uveitis

Intermediate uveitis

Uveitis in JIA

Uveitis with JIA

Retinal vasculitis

Sarcoidosis

Behcet's disease

Toxoplasmosis

Strabismus

Overview

Viral uveitis

Esotropia

Fungal uveitis

Mycobacterial uveitis

Adnexal masses

Exotropia

Spirochaetal uveitis (including Syphilis)

Melanoma

Nematode uveitis

Retinoblastoma

Retinoblastoma (for Part 2)

Incomitent

Voyt-Koyanagi-Harada syndrome

Conjunctival intraepithelial neoplasia

Vertical deviations

Orbit

Sympathetic ophthalmia

AV Malformations and hamartomas

Arteriovenous malformations and hamartomas

Restriction syndromes

Paediatrics

Leucocoria

Congenital Cataract

Paediatric Glaucoma

Retinopathy of prematurity

Retinopathy of Prematurity

ROP-like disorders

Congenital nasolacrimal duct obstruction

White dot syndromes

Aniridia: Short Arm 11 Deletion (11p13)

Choristomas

Management Of Amblyopia

Alphabet patterns

Iris Nodules

Scleritis

Meningioma

Strabismus surgery

Optic nerve glioma

Lymphoma

Rhabdomyosarcoma

Idiopathic orbital inflammation

Orbital neuroblastoma

Anterior Persistent Foetal Vasculature

Lacrimal system

Metastatic lesions

Surgical Retina

Retinal Detachment

Vitreoretinal Interface And Macular Hole

Epiretinal Membrane

Medical Retina

Diabetic Eye Disease

Orbital Blood Vessels

Retinal Vascular Disease

Macular Degeneration

Central Serous Chorioretinopathy (CSCR)

Sickle Cell Retinopathy

Retinitis Pigmentosa

Albinism

Retinal Telangiectasias

Miscellaneous Retinopathies

Atropine And Myopia Progression

Pharmacology

Side Effects Of Systemic Drugs

Foetal Alcohol Syndrome

Neuro-ophthalmology

Optic Neuropathy

Papilloedema

Idiopathic Intracranial Hypertension

Chiasmal Disorders

Retrochiasmal Disorders

Migraine

Paranasal Sinuses

Supranuclear Motility Disorders

Third Nerve Palsies

Fourth Nerve Palsies

Sixth Nerve Palsies

Seventh Nerve Palsies

Anisocoria

Myasthenia Gravis

Myopathies

Blepharospasm

Functional Visual Loss

Lacrimal Glands

Phakomatoses

Developmental diseases

Tear Film

Eyelids

Blinking

Lid Malpositions

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Pigmented Conjunctival Lesions

Squamous Cell Carcinoma Of The Conjunctiva

Ocular Cicatricial Pemphigoid

Cornea

Corneal Structure And Development