The Cornea Flashcards
Layers of the cornea
- Praecorneal tear film
- Epithelium
- Stroma
- Descemet’s membrane
- Endothelium
Completely transparent & avascular
Cornea: Oedema
- Accumulation of fluid in the stroma
- Impaired function of the epi- and/or endothelium
- Water molecules enforce fibres and cells
- Grey-blue opacity; Focal or diffuse
Cornea: Vascularisation
- During both pathologic & healing processes
- Superficial/deep/mixed
- Type of vascularisation depends on the depth of the corneal process
Cornea: Pigmentation
- Pigment deposition in the epithelium & stroma
- Migration of melanocytes & pigment-filled macrophages from the limbus
- Causes: Chronic corneal irritation; Desscication; Exposition
Cornea: Ulceration
- Superficial or deep excavation in the corneal tissue
- At the site of the ulcer, corneal tissue is lost
- Deep ulcers may lead to corneal perforation
Cornea: Infiltration
Features of infiltration are dependent on the cause:
- Leukocytes & granulocytes → Infection
- Eosinophils → Allergy; Antigen-caused
Cornea: Scar formation
- Reparation of gaps in the stroma
- After scarring, irregular arrangement of collagen fibres → Opacity
- Kerectasia
Cornea: Types of scars by size
- Nebula
- Macula
- Leucoma
Cornea: Kerectasia
Severe granulation due to chronic irritation
Corneal congenital opacity: Aetiology
Inherited; Intrauterine infection
Corneal congenital opacity: CSx
- Grayish opacities
- Shape, size and placement varies
Corneal congenital opacity: Treatment
- Limited
- Vision is not severely impaired
- No progression of the disease
Keratitis
Inflammation of the cornea
Keratitis can be classified by…
- Aetiology
- Depth
- Appearance
Keratitis: Classifications by aetiology (10)
- Infectious
- Traumatic
- Allergic
- Associated with systemic disease
- Mechanical
- Chemical
- Irritation
- Desscication
- Innervation abnormalities
- Chronic corneal oedema
Keratitis: Classification by Depth
- Superficial
- Interstitial
- Deep
Keratitis: Classification by appearance
- Ulcerative
- Non-ulcerative
Ulcerative keratitis
Ulcer formation in the cornea
- Superficial/deep excavation
- Gap in the corneal epithelium & stroma
Superficial corneal ulcers can be sub-divided into…
- Uncomplicated & simple
- Indolent (causing little pain)
Deep corneal ulcers can be subdivided into…
- Uncomplicated; Non-melting
- Melting
- Desmetocele
Uncomplicated, superficial corneal ulcer: CSx
- Mild lacrimation
- Blepharospasm
- Perifocal oedema
- If the upper stroma is exposed: Fluorescein positive
Uncomplicated, superficial corneal ulcer: Treatment
- Eliminate the cause
- Antibiotic eyedrops
- Topical vitamins
Heals withing 10-14 days
Indolent, superficial corneal ulcer: Synonyms
- Superficial corneal erosion syndrome
- Indolent corneal ulcer
- Refractory corneal erosion
- Boxer ulcer
Indolent, superficial ulcer: Healing time
- Heals slowly/poorly/not at all
- Tend to recur
Indolent, superficial ulcer: Aetiology
Hereiditary
- Separation of the stroma & epithelium
- Due to inadequate development of hemidesmosomes
Indolent, superficial ulcer: CSx
- Lacrimation
- Blepharospasm
- Undermined lip / “rolled-up” appearance of the epithelium
- Exposed stroma
- Fluorescein positive
- Vascularisation is rarely stimulated
Indolent, superficial ulcer: Treatment
Surgery:
- Grid keratotomy
- Superficial keratectomy + third eyelid flap
- Post operative management
Medical therapy is contraindicated
Non-melting, deep corneal ulcer: CSx
- Pain
- Mucupurulent/purulent discharge
- Deep excavation in the corneal (well-defined edge)
- Fluorescein positive
- Perifocal/diffuse corneal oedema
- Circumcorneal vascularisation
- Secondary uveitis
Non-melting, deep corneal ulcer: Treatment
- Eliminate the cause
- Medical therapy: Atropine; Abx; Vitamins
- Surgery
Melting, deep corneal ulcer: Pathogenesis
Formation of proteases & collagenases from:
- PTF leucocytes - Abnormal secretion
- Destroyed corneal epithelium & fibroblasts
- Bacteria (Pseudomonas spp.)
Stroma becomes solved → Melting → Ulcer → Corneal perforation
Melting, deep corneal ulcer: CSx
- Severe pain (blepharospasm & photophobia)
- Purulent discharge
- Diffuse corneal oedema
- Grey-white, gelatin-like material at the base of the ulcer
- Hypopyon
- Secondary uveitis
Melting, deep corneal ulcer: Treatment
- Emergency intervention
- Elimination of the cause
- Surgery:
- Microsurgery + Enzyme elimination
- Chemical coagulation - Jodine; Phenol
Medical therapy is contraindicated!
Descmetocele: Define
Form of ulcer where the stroma has thinned so much, that the integrity of the eyeball is maintained only by the Descemet membrane
Descemetocele: CSx
- Black & shining
- Mucopurulent discharge
- Pain
- Staining by fluorescein
Descemetocele: Treatment
- Emergency intervention
- Eliminate the cause
- Medical therapy is contraindicated
- Surgery: Direct suturing of cornea
List the operative treatment techniques of deep corneal ulcers
- Grid keratotomy
- Pedicle conjunctival graft transposition
- Free island conjunctival graft transplantation
- Direct suturing of the cornea
Supportive techniques in the therapy of deep corneal ulcers
- Third eyelid flap
- Tarsoraffy (subpalpebral drainage)
- Post-operative mediation: Atropine; Abx; NSAID
- Physical protection of the eye
Special forms of ulcerative keratitis
- Multipunctional keratitis
- Herpetic keratitis
- Corneal sequestrum
Infectious bovine keratoconjunctivitis: Aetiology
“Pink eye”
- Moraxella bovis (via flies)
- Adheres to the cornea
- Haemolysin, dermo-necrolysin & collagenase
- Ulceration & necrosis of the cornea
Infectious bovine keratoconjunctivitis: Summary
“Pink eye”
- Frequent disease
- Deep, melting & necrotic ulcer
Infectious bovine keratoconjunctivitis: CSx
- Uni-/bilateral
- More severe in summer & young animals
- Pain & lacrimation
- Central corneal ulcer
- Diffuse, pinkish corneal opacity
- Corneal vascularisaiton
- Descemetocele, corneal perforation, phthitis
Infectious bovine keratoconjunctivitis: Treatment
- Separation of diseased animals using fly repellants
- Sub conjunctival depocillin/tetracycline
- IV sulphonamides
- Tarsorraphy/third eyelid flap (if severe)
- Subconjunctival steroids
Non-ulcerative keratitis: Definition
Inflammation of the superficial/ deeper layers of the cornea without ulcer formation
- Uberreiter’s syndrome
- Pigmentary kereatitis
- Endothelial syndrome
Überreiter’s syndrome: Synonyms
- Chronic immune-mediated KCS
- Chronic superficial keratitis
- Pannus
Usually seen in German Shepherds
Überreiter’s syndrome: Aetiology
Unknown; Autoimmune; Role of UV radiation & viruses
- Proliferation of epithelial cells
- Infiltration of the superficial stroma by plasma cells & lymphocytes
- Vascularisation & lipid deposition; Pigmentation, oedema; Scar tissue formation
Überreiter’s syndrome: CSx
- Bilateral
- Temporal inferior corneal quadrant will be opaque
- Opacity will gradually move centrally → Whole cornea
- Opacity appears red-grey/black
- Fluorescein negative
- May have a “third eyelid form”
What is shown?
Überreiter’s syndrome: Third eyelid form
Überreiter’s syndrome: Treatment
Cannot be cured
- Medical management:
- Subconjunctival & topical steroids
- Topical cyclosporin
- Surgical management:
- Superficial keratectomy
- Post-operative therapy
Trauma to the cornea: Aetiology
- Biting
- Scratching
- Kicking
- Accident
- Foreign body
- Surgery
Trauma to the cornea: CSx (superficial)
- Loss of epithelium
- Oedema
- Pain
Trauma to the cornea: CSx (Deep)
- Deep gap in the stroma
- Diffuse oedema
- Opacity
- Severe pain
- Discharge
Perforation/laceration?
Trauma to the cornea: Perforation
- Full thickness injury of the cornea with outflow of aqueous humor
- Severe pain
Trauma to the cornea: Perforation-laceration
- Perforation together with widespread rupture
- Prolapse of the iris-lens vitreous
- Severe pain
Trauma to the cornea: Treatment (Superficial & deep)
Similar to ulcer therapy
Trauma to the cornea: Treatment (perforation)
- Surgical therapy
- Conjunctival graft; Direct suturing
