Eye and Orbit

• How is venous blood drained out of the eyeball?

  Superior & inferior ophthalmic vein which largely drain into cavernous sinus but can also drain into pterygoid plexus of veins

  
  

  - there are no valves so blood can flow in any direction (can be a source of infection as bacteria can get in)

  
• why is the Central artery of retina an end artery?

  because it is the only artery that supplies blood to the retina.

  - there is no backup

  (if there is a blockage, it will cause death of the cells in the retina and cause blindness)
• What provides blood supply to the retina?

  Central artery of retina (branch of ophthalmic artery)

  
• Where does the anterior blood supply to the orbit come from?

  Ophthalmic artery (branch of internal carotid artery)

  
• What passes through the superior orbital fissure?

  C.IV

  C.V1- frontal branch

  C.V1- lacrimal branch

  C.V1- nasociliary branch

  C.III- superior branch

  C.III- inferior branch

  
• What passes through the optic canal?

  - Optic nerve (C.II)

  - Ophthalmic artery

  
• what does the the sympathetic nervous system innervate in the eyeball?

  - dilator pupillae which causes pupil dilation

  - superior tarsal muscle which lifts up the eyelid
• Where does sympathetic innervation to the eye originate from?

  Upper thoracic spinal cord
• what does the the parasympathetic nervous system innervate in the eyeball?

  - sphincter pupillae which causes pupil constriction

  - ciliary muscle which causes accommodation of the lens
• Where does parasympathetic innervation to the eye come from?

  Ciliary ganglion
• What does the autonomic innervation of the eye look like?

  
• What are the extra-ocular muscles innervated by?

  ALL OF THEM = CN III

  
  

  EXCEPT:

  - lateral rectus= CN VI

  - superior oblique= CN IV

  
  

  (LR6SO4= helps to remember)

  
• What does medial and lateral rectus do?

  Lateral rectus causes abduction

  Medial rectus causes adduction

  
• What does superior and inferior oblique do?

  - Superior oblique causes depression & abduction

  - Inferior oblique causes elevation & abduction

  
• What does superior and inferior rectus do?

  - Superior rectus causes elevation (& also adducts a bit due to the angle of the orbit)

  - Inferior rectus causes depression

  
• Which 6 extra-ocular muscles move the eyeball?

  - Superior rectus/ inferior rectus

  - Superior oblique/ inferior oblique

  - Lateral rectus/ medial rectus

  
• the axis of the eye ball and the axis of the orbit are angled differently when you look straight ahead.

  TRUE/FALSE

  TRUE

  
  

  -> This is important as the muscles are anchored at a tendonous ring at the apex of the orbit. This means the angle that the muscles will be acting on is not the same as the axis of the eyeball.

  
• What are the different movements of the eye?

  main ones:

  
  

  up= elevation

  down= depression

  medially= adduction

  laterally= abduction

  
• What do the ciliary muscles do to focus on near objects?

  Ciliary muscles contract, releases tension in zonal fibres (zonules of Zinn), makes lens rounder.

  
  

  -> Increased curvature of lens means focal point shifts closer to eye

  
• why are our eyes focused on objects in the mid-distance at rest?

  the lens is stretched by zonules of zinn, making it flatter.

  
• What does the ciliary muscle control?

  Shape of lens and, therefore, focus

  = ACCOMODATION

  
• Which 2 involuntary muscles control the size of the pupil?

  Dilator pupillae- radially arranged, sympathetic innervation

  
  

  Sphincter pupillae- circularly arranged, parasympathetic innervation

  
• What does the ciliary process do?

  Secretes aqueous humour.

  
  

  The iris lies on anterior surface of lens & is a thin contractile diaphragm with a central aperture (pupil) for transmitting light

  
• What is the ciliary body?

  A ring-like thickening of the layer posterior to the corneoscleral junction that is muscular as well as vascular and provides attachment for lens

  
• Describe the retina of the eye.

  Light sensitive, neural part of eye

  
• Describe the choroid of the eye.

  Dark red-brown colour so pigmented & highly vascular, continuous with ciliary body & iris

  
• Describe the sclera of the eye.

  Dense & white

  
  

  - provides the attachment for all muscles of the eye

  - relatively avascular (no blood vessels or lymphatic system)

  - continuous with transparent cornea (completely avascular)

  
• What are the 3 layers of the eyeball?

  - Sclera

  - Choroid

  - Retina
• What can damage to the facial nerve (C.VII) do?


  Leads to paralysis, preventing eyelids from closing fully & eversion of lower eyelid, which in turn can cause drying & damage to cornea
• what is the orbicularis oculi innervated by?

  facial nerve (C.VII)
• What does the palpebral part of the orbicularis oculi do?

  Close eyes during sleep & blinking

  
  

  -> rest of muscle used to screw eyes tightly shut for protection

  
• Where is orbicularis oculi located?

  Subcutaneous tissue outside of the tarsal plate in both upper & lower eyelid

  
• What can cause ptosis (drooping eyelid)?

  Loss of function of either lev palp sup (e.g. C.III lesion) or sup tarsal (e.g. sympathetic lesion)
• What also raises the eyelid in companion with levator palpebrae superioris?

  A collection of smooth muscle fibres called superior tarsal muscle (some consider it part of lev palp sup).

  
  

  - Innervation is from sympathetic fibres from sup cervical ganglion

  
• What is the levator palpebrae superioris?

  Muscle only in upper eyelid- raises eyelid (innervation by C.III), and inserts into tarsus

  
• how are tears formed?

  When produced in excess, lacrimal fluid forms tears.
• once lacrimal fluid is produced, what happens when the eyelids blink?

  when the eyelids blink, they push the lacrimal fluid medially over the cornea.

  
  

  - Fluid containing foreign material is pushed to medial angle of eye and drains through lacrimal canaliculi into lacrimal sac. The nasolacrimal duct conveys fluid to nasal cavity

  
• What is production of lacrimal fluid stimulated by?

  Parasympathetic impulses from C.VII and secreted through lacrimal ducts to surface of conjunctiva

  
• What is the conjunctiva important for?

  helps to ward of infectious agents and trigger an immune response
• What is the conjunctiva?

  A transparent mucous membrane, one cell layer thick, that lines the inside of the eyelids and covers anterior surface of eyeball, except cornea