Eye & Ear Anatomy

• The orbit

  žBony cavities of facial (viscerocranium) bones.

  žHollow, bilateral cone-shaped chambers.

  
• The orbit Houses:

  •Eyeball

  •Fascial ‘suspensory apparatus’ sheath

  •Fat (acts as cushions)

  •Optic nerve (CN II)

  •Extra-ocular muscle

  •Other nerves associated with the eye: Oculomotor nerve (CN III), Trochlear nerve (CN (IV), Abducens nerve (CN VI), Trigeminal nerve (CN V1 Ophthalmic division).

  •Vasculature orbits: Ophthalmic arteries & veins

  •Lacrimal gland

  
• The orbit:

  Axis of orbit: diverge at 45°.

  Axis of eyeball: looking straight ahead.

  
• Fascial ‘suspensory apparatus’ sheath attaches to the sclera of eye. connective tissue that helps to support the eye as it sits within the orbit. .The sheath separates the eye from orbital fat and forms a socket for the eye to sit in.
• The bony orbit = •Function: Protects eye and associated muscles, vessels and nerves from direct trauma.

  
• Bony walls:

  •Orbital rim

  –Frontal, maxilla & zygomatic bones

  •Superior wall

  –Frontal

  –Lesser wing of sphenoid

  •Lateral wall

  –Zygomatic

  –Greater wing of the sphenoid

  •Medial wall

  –Ethmoid

  –Contributions from maxilla, Lacrimal & sphenoid

  •Inferior wall

  –Maxilla

  –Contributions from zygomatic & palatine

  
• Orbital rim

  –Frontal, maxilla & zygomatic bones

  
• •Superior wall

  –Frontal

  –Lesser wing of sphenoid

  
• •Lateral wall

  –Zygomatic

  –Greater wing of the sphenoid

  
• •Medial wall

  –Ethmoid

  –Contributions from maxilla, Lacrimal & sphenoid

  
• •Inferior wall

  –Maxilla

  –Contributions from zygomatic & palatine

  
• The eyelids

  žPalpebral fissure: The gap or opening between the two eyelids.

  
• žFunction of the eyelids:

  —Protect the surface of the eyeball when closed.

  —Distributes lacrimal fluids over the surface of eyeball.

  
• The eyelids

  5 main layers (superficial to deep):

  —Skin and subcutaneous tissue

  —Orbicularis oculi muscle:

  —Tarsal plates

  —Levator apparatus: (only in upper eyelid) Levator Palpebrae Superioris and Superior tarsal muscle.

  —Conjunctiva

  
• The eyelids

  —Orbicularis oculi muscle:

  •MoFE, functions to CLOSE eyelids.

  •Innervation: Facial n. (CNVII).

  
• The eyelids

  —Tarsal plates;  connective tissue that helps give shape to the eyelid as well as give some attachment points for muscles like the levator apparatus 

  
• The eyelids

  —Levator apparatus: (only in upper eyelid) Levator Palpebrae Superioris and Superior tarsal muscle.

  • Functions to ELEVATE the eyelid.

  • Innervation: Levator palpebrae superioris – CN III.  Superior Tarsal m. – Sympathetic (sup. Cervical ganglion).

  • Damage can result in “ptosis” (droopy eye)

  
• • Innervation: Levator palpebrae superioris – CN III.  Superior Tarsal m. – Sympathetic (sup. Cervical ganglion).
• •Conjunctiva: thin mucous membrane that lines the internal surface of the  eyelid (palpebral part) and covers the sclera ‘whites of eyes’ (bulbar part) except for the cornea. The junction between the bulbar and palpebral part is called conjunctiva fornix. It attaches to the eyeball at the junction between the sclera and the cornea.

  
• •The space between the eyeball and the eyelid is the conjunctival sac.

  
• Conjunctiva

  •Function: Conjunctival goblet cells — forms mucus part of tears, has antimicrobial properties. Acts like a ‘raincoat’ for eyes to maintain moisture and lubrication.

  
• Conjunctivitis ‘Pink eye’ – inflamed and irritated conjunctiva membrane. Capillaries in conjunctiva becomes swollen gives appearance of eye to become reddish or pink. 

  
• •Subconjunctival haemorrhage – capillaries in conjunctiva burst causing blood to leak between conjunctiva and sclera. Vision is not impacted because blood is not on cornea.

  
• Lacrimal apparatus

  žConsists of Lacrimal gland and the system of ducts and channels that collects the lacrimal fluid and drains them into the nasal cavity.

  žLacrimal gland located in lacrimal ‘fossa’ of frontal bone – a depression located anteriorly in the superolateral aspect of the orbital plate of frontal bone.  

  žLacrimal fluid acts to clean nourish and lubricate the eyes. Tears form when produced in excess.  

  
• Lacrimal apparatus

  The continuity between the conjunctiva and the nasolacrimal duct and nasal mucosa is important in the spread of infection.

  
• Lacrimal apparatus

  Parasympathetic innervation from Facial nerve (CN VII)

  • Stimulates lacrimal fluid production.

  
• Lacrimal apparatus

  Fluid is ‘spread’ over the cornea by the process of blinking.

  
• Flow of lacrimal fluid:

  1. Lacrimal gland produces tears
  2. Lacrimal ducts
  3. Conjunctival sac (ocular surface)
  4. Lacrimal lake in medial canthus of eye
  5. Lacrimal canaliculus
  6. Lacrimal sac
  7. Nasolacrimal duct
  8. Inferior meatus of Nasal cavity.

  
• The Eyeball proper

  žOccupies anterior part of orbit.

  žMajority of the eyeball is spherical, with exception of the cornea that projects outwards anteriorly.  

  žContains the optical apparatus of the visual system.

  
• MRI T1-weighted: Fat is bright.

  Axial head MRI - T1 weighted

  A) ethmoid sinus

  B) cornea

  C) lens

  D) optic nerve

  
• Eyeball proper is formed by 3 layers, each has a specialised structure and function:

  1.Fibrous layer (Outer coat)

  •Sclera, cornea

  2.Vascular & Muscular layer(Middle coat)

  •Choroid, ciliary body, iris

  3.Neural layer (Inner coat)

  Retina (Light detecting component)

  
• The Eyeball proper

  A) sclera

  B) cornea

  C) corneal limbus

  D) meningeal covering

  E) choroid

  F) cilliary body

  G) iris

  H) pupil

  I) macula

  J) cilliary processes

  K) retinal pigment epithelium

  L) optic disc

  M) ora seratta

  N) optic part of retina

  O) non visual part of retina

  
• The Eyeball proper: Fibrous layer

  External fibrous ‘skeleton’ of eyeball, provides shape and structural support to deeper eye structures.

  
• Sclera (“White of the eye”):

  —Opaque , dense connective tissue covering 5/6th of eyeball.  

  —Provides attachment for extra-ocular eye muscles (muscles for eyeball movement).

  
• Cornea:

  —Transparent, covering anterior 1/6th of eyeball.

  —Completely avascular – allows light to pass through.

  —Sensory innervation: Ophthalmic n. (CN V1).

  
• Capillary beds around its periphery of sclera,

  lacrimal fluids and aqueous humour provide nourishment to avascular fibrous layer of eye. - Cornea
• Aqueous humour - This clear watery solution provides nutrients for the avascular cornea and lens.
• Middle layer of eyeball has 2 parts: a vascular part and muscular part.

  
• The Eyeball proper: Middle layer:

  Vascular part provides oxygen and nutrients to the underlying retina layer:

  •Choroid “pigmented dark red brown”:

  — Thin, highly vascular and lines most of the sclera and retinal layer.

  — Continuous anteriorly with muscular parts: the ciliary body and iris.

  
• middle layer

   The vasculature of the choroid supplies nutrients to the avascular retina.

  A thin choroid lying posteriorly, a thicker ciliary body and an anterior iris that is displaced from the outer coat and terminates at the pupillary aperture.