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Flashcards about the cornea, corneal diseases, and related topics, based on lecture notes.
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What is the cornea?
The anterior transparent 1/6 of the outer coat of the eye ball.
What is a key characteristic of the cornea related to blood vessels?
Avascular except for 1 mm at the limbus.
What are the average vertical and horizontal diameters of the adult cornea?
11 mm vertically and 12 mm horizontally.
What is the corneal thickness peripherally and centrally?
0.67 mm peripherally and 0.52 mm centrally.
What is the refractive index (R.I) of the cornea?
1.37
What is the refractive power of the cornea?
42 diopters
How many layers form the cornea, and what are they?
Six layers: epithelium, Bowman’s layer, stroma, Dua layer, Descemet’s membrane, and endothelium.
Describe the corneal epithelium.
A stratified squamous non-keratinized epithelium formed of 5-6 layers of cells.
What is Bowman's layer?
A clear acellular condensation of the superficial corneal stroma that cannot regenerate after injury.
What is the stroma of the cornea formed of?
Collagen lamellae (100-200) which are regularly arranged.
What is the Dua layer?
A condensation of posterior stroma.
What is Descemet's membrane?
An elastic membrane resistant to digestion by proteolytic enzymes.
Describe the corneal endothelium.
One layer of flat hexagonal cells containing Na/K pump (endothelial pump).
What is the limbus?
Semitransparent, vascularized transition zone between the conjunctiva/sclera and the cornea.
What provides the nerve supply to the cornea?
Nasociliary nerve (branch of ophthalmic nerve).
From what sources does the cornea receive nutrition?
Air, tear film, limbal capillaries, and aqueous humor.
What is a corneal abrasion?
Loss of corneal epithelium.
What are the symptoms of corneal abrasion?
Ocular pain, photophobia, lacrimation, and blurred vision.
What is the treatment for corneal abrasion?
Ocular bandage, antibiotics, and analgesics.
What is superficial keratitis (corneal ulcer)?
Superficial corneal inflammation leading to stromal loss associated with epithelial and Bowman's membrane involvement.
What types of non infectious primary corneal ulcers are there?
Traumatic, Neuroparalytic, Mooren's, Atheromatous, Keratomalcia, Ulcer with lagophthalmous.
What are some local predisposing factors for infectious corneal ulcers?
Corneal trauma, xerosis, loss of sensation, toxicity of topical drugs, immunosuppresion.
What are some general predisposing factors for infectious corneal ulcers?
DM, liver/renal failure, malignancies, AIDS, malnutrition, pregnancy.
Name some bacterial causative organisms of corneal ulcers.
Pneumococci (most common), Pseudomonas (most dangerous), DNHL.
What are some viral causes of corneal ulcers?
Herpes simplex and zoster
What are some fungal causes of corneal ulcers?
Candidiasis and Aspergillosis
What protozoal organism can cause corneal ulcers?
Acanthamoeba (common in contact lens wearers).
What are the three stages of a corneal ulcer?
Infiltration, ulceration, and healing.
What are the symptoms of a corneal ulcer?
Pain, photophobia, lacrimation, belpharospasm, and diminished vision.
What is the local treatment for uncomplicated corneal ulcer?
Cycloplegics, eye bandage, specific antimicrobial drugs, and hot fomentation.
What is the systemic treatment for uncomplicated corneal ulcer?
Analgesics and vitamins.
How is secondary glaucoma treated as a complication of corneal ulcer?
Glaucoma treatment (beta-blockers and CAIs). Pilocarpine is contraindicated.
How is descematocele treated as a complication of corneal ulcer?
Complete rest, sedation, eye shield, avoid straining, and lowering of IOP.
How is perforation treated as a complication of corneal ulcer?
Tissue glue (small) or patching graft/keratoplasty (large).
How is central nebula treated as a complication of corneal ulcer?
Glasses or lamellar keratoplasty.
How is leucoma treated as a complication of corneal ulcer?
Penetrating keratoplasty (seeing eye) or cosmetic keratoplasty (blind eye).
What are resistant Corneal Ulcers?
Ulcers that don't respond to specific treatment for at least 2 weeks.
What are treatment options for resistant corneal ulcers?
Culture and sensitivity, debridement, subconjunctival injection of antibiotics, therapeutic contact lenses, cauterization, conjunctival graft, or therapeutic keratoplasty.
What is a Hypopyon ulcer?
Primary infective corneal ulcer with severe iridocyclitis and accumulation of hypopyon in the anterior chamber.
Name a causative organism of Hypopyon ulcer.
Pneumococci (80%), Moraxella, staph, strept (20%).
Which causative organism is responsible for Viral Keratitis?
Varicella zoster.
Which causative organism is responsible for Fungal Keratitis?
Fungi such as Candida or Aspergillous
Which causative organism is responsible for Acanthameoba Keratitis?
Acanthameba.
What is the pathogenesis of Ulcer with lagophthalmos?
Exposure of the lower 1/3 of the cornea due to Bell’s phenomenon, leading to dryness and ulceration
What is Keratomalacia?
Melting of the cornea due to vitamin A deficiency in severely malnourished children.
What is the treatment for Keratomalacia?
Large doses of systemic vitamin A, treatment of hypoproteinemia, antibacterial drugs, vitamin A eye ointment.
What is Neurotrophic (Neuroparalytic) Keratitis?
Loss of corneal sensation leading to trophic changes.
What is Mooren’s Ulcer?
A rare, primary, chronic serpiginous ulcer of unknown etiology, more common in the elderly.
What is Atheromatous Ulcer?
Occurs in the area of an old leucoma due to hyaline degeneration with desquamation and secondary infection.
What are Secondary Corneal Ulcers?
Superficial keratitis occurring as a complication of another ocular lesion.
What is Arcus Senilis?
Bilateral, peripheral lipoidal infiltration of the corneal stroma in old age.
What is Anterior Keratoconus?
Anterior, non-inflammatory ectasia of the central part of the cornea.
What are the treatment options for Keratoconus?
Glasses, collagen cross-linking, intra-corneal rings, or penetrating keratoplasty.
What is Keratoglobus?
A congenital, bilateral, globular configuration of the cornea.
What is Keratoplasty?
Replacing an opaque part of the cornea with a clear cadaveric one.
What are the indications for keratoplasty?
Optical, therapeutic, structural, and cosmetic.