Cornea & Sclera Flashcards
What are the 5 layers of the cornea?
1) Epithelium
2) Bowman membrane
3) Stroma
4) Descemet membrane
5) Endothelium
What is the histology of the corneal epithelium?
Non- keratinized stratified
squamous
The corneal epithelium regenerates from __ found in the __.
Stem cells; Limbus
Which layer gives 90% of the corneal thickness? Which fibrils does it contain?
Stroma; parallel collagen fibrils
What is the role of the corneal endothelium?
Non-regenerating cells that actively pump water from the stroma to control hydration of the cornea
What happens if the corneal endothelium is damaged?
1) Edema
2) Corneal clouding
The cornea derives its nutrition almost entirely from:
Aqueous humour
The cornea is rich in sensory nerve endings originating from:
The nasociliary branch of trigeminal nerve
What is the function of the cornea?
1) Protection of internal ocular structures
2) Refraction
Refractive components of the eye or the focusing power is:
1) 2/3 cornea, fixed power
2) 1/3 lens, power increases with accommodation
Herpes Simplex and Zoster Keratitis are characterized by:
The appearance of dendritic ulcers on the cornea, which usually heal without scar
Which virus is the most common cause of Herpes Simplex and Zoster Keratitis?
HSV-1
What are the signs & symptoms of Herpes Simplex and Zoster Keratitis?
1) Very painful
2) Photophobia
3) Watery discharge
4) Eyelid swelling
5) Dendritic ulcer
The pathognomonic appearance of Herpes Simplex and Zoster Keratitis is:
Dendritic ulcers
How do HZV skin lesions start?
As vesicles at ophthalmic division of trigeminal
HZV ocular problems are more likely if:
The nasociliary branch is involved = Hutchinson’s sign
Treatment for Herpes Simplex and Zoster Keratitis lesions?
1) Topical antiviral for dendritic ulcer (acyclovir)
2) Oral antiviral in HZV with skin involvement, will reduce post herpetic neuralgia
Should topical steroids be used in patients with dendritic ulcers?
No; they may cause more extensive ulceration
The cornea is protected against infection by:
1) Blinking
2) Washing of debris by the flow of tears
3) Entrapment of foreign particles by mucus
4) Anti-microbial properties of tear
5) The barrier function of the corneal epithelium
__ is the only organism
that can penetrate the intact corneal epithelium
Neisseria gonorrhoeae
Predisposing factors for bacterial keratitis:
1) Keratoconjunctivitis sicca (dry eye)
2) A breach in the corneal epithelium
3) Contact lens use
4) Prolonged use of topical steroids
Signs & symptoms of bacterial keratitis?
1) Pain
2) Purulent discharge
3) Ciliary injection
4) Visual loss
5) Hypopyon
What is hypopyon?
White cells collected in the anterior chamber
Treatment of bacterial keratitis?
1) Combined topical antibiotics to cover G+ve and G-ve
2) Fluorquinolones can be used as monotherapy
Acanthameba Keratitis is caused by:
Protozoa
Ring shaped abscesses are found in __.
Acanthameba Keratitis
Acanthameba Keratitis treatment?
Chlorhexidene and propamidine for months and may end by corneal graft
Fungal Keratitis should be considered in:
1) Lack of response to antibacterial therapy
2) Cases associated with prolong use of steroids
3) History of trauma by plants
Corneal dystrophies are divided into:
1) Anterior Dystrophies
2) Stromal Dystrophies: present with visual loss
3) Posterior Dystrophies: gradual visual loss
Anterior corneal dystrophies present with:
Recurrent corneal erosion
What is Keratoconus?
Sporadic disorder associated with thinning of the center of the cornea leads to ectasia and cone shaped cornea
Signs & symptoms of keratoconus?
1) Myopia
2) Astigmatism
NO PAIN
How is keratoconus diagnosed?
Corneal topography
Keratoconus treatment?
1) Spectacles
2) Contact lenses
3) Corneal cross linking
4) Intra stromal corneal rings
5) Corneal graft
6) CROSS LINKING
What is the sclera composed of?
Interwoven collagen fibrils of different widths
All six extraocular muscles are inserted on the __.
Sclera
Scleritis is usually associated with __.
Collagen vascular disease most
commonly RA
Complications of scleritis?
1) Sclermalacia (scleral thinning) sometimes with perforation
2) Keratitis
3) Uveitis
4) Cataract formation
5) Glaucoma
Management of mild scleritis?
Topical steroids and oral NSAIDs
Management of moderate and severe scleritis?
By high doses of systemic steroids or Cytotoxics
