NS16 Eyes

NS16 Eyes

1. Eyelids

   • Functions
     • Barrier to mechanical damage of cornea
     • Distribute tear film during blinking (vital for corneal health)
     • Secretory function
       • Tarsal (Meibomian) gland secrete lipid (outer layer of tear film)
   • Anatomy
     • 3 layers
       • Outer layer (thin skin)
       • Middle layer (Glands, muscles, CT)
         • Tarsal plate confers rigidity
         • TARSAL GLANDS = a row of tiny openings. Secrete lipid
       • Inner layer (palpebral conjunctiva)
   • Cilia (eyelashes)
     • Cats don't have any eyelashes at all
     • Dogs & horses only have top lashes
     • Just in front of tarsal glands

2. Conjunctiva

   • = Thin, vascular membrane
   • PALPEBRAL conjunctiva is reflected @ base of lids to continue on sclera as BULBAR conjunctiva
   • 1. Palpebral conjunctiva
     • line sinner surface of lids
     • Pinker than Bulbar conjunc. because right under bulbar conjunc. is sclera which is white
   • 3. Nicititans conjunctiva
     • Third Eyelid
       • = A dorsoventrally oriented conjunctival fold between lacrimal caruncle & eyeball
       • Covered w/ conjunctiva on both sides
       • Invisible when eye is closed
       • Supported by a T-shaped cartilage
         • Bar lies in free edge of fold
         • Stem points backwards into orbit (medial to eyeball)
           • Stem surrounded by the Gland of 3rd eyelid
       • Cherry eye = prolapse of gland in 3rd eyelid
     • over cartilage of 3rd eyelid
   • 2. Bulbar conjunctiva
     • Covers globe. Terminates @ limbus

3. Lacrimal system (Tears)

   • Production
     • Outer layer: Lipid by tarsal gland
       • To prevent evaporation
     • Middle layer: Aqueous by Lacrimal gland & Nicitans glands
     • Inner layer: Mucus by conjunctival goblet cells
       • For adhesion to cornea
   • Distribution
     • By eyelids (during blinking) & 3rd eyelid (~windscreen)
   • Drainage
     • By Punctae (upper & lower), Caniliculi, Lacrimal sac & Nasolacrimal duct, Nasal ostium
   • Lactoferrin in tear film - antimicrobial & anti-inflammatory

4. Orbit - protective role

   • Protect eyeball except cornea
   • Gap in dorsolateral segment - closed by orbial ligament
     • To accomodate widening the jaw in predators
   • More bony margins in dogs

5. Anatomical relationships of globe as ocular tunics, lens & ocular media (aqueous & virtreous)

6. Classifications of anterior & posterior segments, anterior & posteriod poles & equator - diagram!

7. Ocular tunics - Collagenous layer (cornea & sclera), Vascular layer (Uvea), Nervous layer (Retina)

   • Outer Collagenous Layer
     • Cornea
       • Cornea is continuous w/ sclera
       • Transparent
       • 4 layers
         • 1. Epithelium
           • Lose cells into tear film
           • Columnar cells
         • 2. Stroma
         • 3. Descemet's membrane
         • 4. Endothelium
     • Sclera
     • For rigidity & support
   • Middle Vascular Layer (Uvea)
     • Iris & Ciliary Body (Anterior Uvea)
       • Iris
         • Readily visible
         • Colour
         • Shape of pupil
         • Granulae iridcae
           • = Pigmented roughened prominences along the pupillary margin of horses. An extension of the posterior iris epithelium
           • consist of 2 layers of pigmented epithelium
           • to augment the effectiveness of pupillary constriction in bright light
         • = Third & smallest part of vascular tunic
         • Suspended between cornea & lens
         • = a flat ring of tissue attached @ its periphery to sclera (by *Pectinate ligament*) and ciliary body
         • Pupil = the opening in the middle
       • Ciliary body obscured by iris (Even when pupil is dilated to the max)
     • Choroid (Posterior Uvea) (Vascular)
       • Black. @Back of eye
   • Inner Retinal Layer
     • Photoreceptors for light detection
     • Lines inside of globe @ back of eye
     • Neuroretina
       • Photoreceptors @ outer layer
       • Ganglion cell axons of inner layer converge to form OPTIC n.
     • Retinal pigment EPT

8. Histology of Cornea (Corneal injury)

9. Modulation of pupil size

   • Dilator muscle (Sympathetic)
   • Constrictor muscle (Parasympathetic)
   • Mydriatics dilate pupil
     • Parasymathetic (most common in clinics - anti-muscarinic) or Sympathetic agents
   • Miotics constrict pupils

10. Production & outfow of aqueous. Relationship between anterior & posterior chambers

11. Lens

12. Anatomical basis for ophthalmoscopic appearance of FUNDUS

13. Extraocular Muscles

    • Rectus Muscles
      • Dorsal (III), Ventral (III), Medial (III), Lateral (VI)
    • Retractor bulbi (VI)
      • To retract eyeball into orbit (except humans)
        • Asso. w/ blinking (Facial n. CN 7)
    • Dorsal oblique (IV)
    • Ventral oblique (III)

14. Predators: Binocular & Stereoscopic