Cornea and Corneal Diseases

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Flashcards about the cornea, corneal diseases, and related topics, based on lecture notes.

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56 Terms

1
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What is the cornea?

The anterior transparent 1/6 of the outer coat of the eye ball.

2
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What is a key characteristic of the cornea related to blood vessels?

Avascular except for 1 mm at the limbus.

3
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What are the average vertical and horizontal diameters of the adult cornea?

11 mm vertically and 12 mm horizontally.

4
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What is the corneal thickness peripherally and centrally?

0.67 mm peripherally and 0.52 mm centrally.

5
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What is the refractive index (R.I) of the cornea?

1.37

6
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What is the refractive power of the cornea?

42 diopters

7
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How many layers form the cornea, and what are they?

Six layers: epithelium, Bowman’s layer, stroma, Dua layer, Descemet’s membrane, and endothelium.

8
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Describe the corneal epithelium.

A stratified squamous non-keratinized epithelium formed of 5-6 layers of cells.

9
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What is Bowman's layer?

A clear acellular condensation of the superficial corneal stroma that cannot regenerate after injury.

10
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What is the stroma of the cornea formed of?

Collagen lamellae (100-200) which are regularly arranged.

11
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What is the Dua layer?

A condensation of posterior stroma.

12
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What is Descemet's membrane?

An elastic membrane resistant to digestion by proteolytic enzymes.

13
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Describe the corneal endothelium.

One layer of flat hexagonal cells containing Na/K pump (endothelial pump).

14
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What is the limbus?

Semitransparent, vascularized transition zone between the conjunctiva/sclera and the cornea.

15
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What provides the nerve supply to the cornea?

Nasociliary nerve (branch of ophthalmic nerve).

16
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From what sources does the cornea receive nutrition?

Air, tear film, limbal capillaries, and aqueous humor.

17
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What is a corneal abrasion?

Loss of corneal epithelium.

18
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What are the symptoms of corneal abrasion?

Ocular pain, photophobia, lacrimation, and blurred vision.

19
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What is the treatment for corneal abrasion?

Ocular bandage, antibiotics, and analgesics.

20
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What is superficial keratitis (corneal ulcer)?

Superficial corneal inflammation leading to stromal loss associated with epithelial and Bowman's membrane involvement.

21
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What types of non infectious primary corneal ulcers are there?

Traumatic, Neuroparalytic, Mooren's, Atheromatous, Keratomalcia, Ulcer with lagophthalmous.

22
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What are some local predisposing factors for infectious corneal ulcers?

Corneal trauma, xerosis, loss of sensation, toxicity of topical drugs, immunosuppresion.

23
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What are some general predisposing factors for infectious corneal ulcers?

DM, liver/renal failure, malignancies, AIDS, malnutrition, pregnancy.

24
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Name some bacterial causative organisms of corneal ulcers.

Pneumococci (most common), Pseudomonas (most dangerous), DNHL.

25
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What are some viral causes of corneal ulcers?

Herpes simplex and zoster

26
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What are some fungal causes of corneal ulcers?

Candidiasis and Aspergillosis

27
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What protozoal organism can cause corneal ulcers?

Acanthamoeba (common in contact lens wearers).

28
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What are the three stages of a corneal ulcer?

Infiltration, ulceration, and healing.

29
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What are the symptoms of a corneal ulcer?

Pain, photophobia, lacrimation, belpharospasm, and diminished vision.

30
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What is the local treatment for uncomplicated corneal ulcer?

Cycloplegics, eye bandage, specific antimicrobial drugs, and hot fomentation.

31
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What is the systemic treatment for uncomplicated corneal ulcer?

Analgesics and vitamins.

32
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How is secondary glaucoma treated as a complication of corneal ulcer?

Glaucoma treatment (beta-blockers and CAIs). Pilocarpine is contraindicated.

33
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How is descematocele treated as a complication of corneal ulcer?

Complete rest, sedation, eye shield, avoid straining, and lowering of IOP.

34
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How is perforation treated as a complication of corneal ulcer?

Tissue glue (small) or patching graft/keratoplasty (large).

35
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How is central nebula treated as a complication of corneal ulcer?

Glasses or lamellar keratoplasty.

36
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How is leucoma treated as a complication of corneal ulcer?

Penetrating keratoplasty (seeing eye) or cosmetic keratoplasty (blind eye).

37
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What are resistant Corneal Ulcers?

Ulcers that don't respond to specific treatment for at least 2 weeks.

38
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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.

39
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What is a Hypopyon ulcer?

Primary infective corneal ulcer with severe iridocyclitis and accumulation of hypopyon in the anterior chamber.

40
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Name a causative organism of Hypopyon ulcer.

Pneumococci (80%), Moraxella, staph, strept (20%).

41
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Which causative organism is responsible for Viral Keratitis?

Varicella zoster.

42
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Which causative organism is responsible for Fungal Keratitis?

Fungi such as Candida or Aspergillous

43
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Which causative organism is responsible for Acanthameoba Keratitis?

Acanthameba.

44
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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

45
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What is Keratomalacia?

Melting of the cornea due to vitamin A deficiency in severely malnourished children.

46
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What is the treatment for Keratomalacia?

Large doses of systemic vitamin A, treatment of hypoproteinemia, antibacterial drugs, vitamin A eye ointment.

47
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What is Neurotrophic (Neuroparalytic) Keratitis?

Loss of corneal sensation leading to trophic changes.

48
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What is Mooren’s Ulcer?

A rare, primary, chronic serpiginous ulcer of unknown etiology, more common in the elderly.

49
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What is Atheromatous Ulcer?

Occurs in the area of an old leucoma due to hyaline degeneration with desquamation and secondary infection.

50
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What are Secondary Corneal Ulcers?

Superficial keratitis occurring as a complication of another ocular lesion.

51
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What is Arcus Senilis?

Bilateral, peripheral lipoidal infiltration of the corneal stroma in old age.

52
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What is Anterior Keratoconus?

Anterior, non-inflammatory ectasia of the central part of the cornea.

53
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What are the treatment options for Keratoconus?

Glasses, collagen cross-linking, intra-corneal rings, or penetrating keratoplasty.

54
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What is Keratoglobus?

A congenital, bilateral, globular configuration of the cornea.

55
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What is Keratoplasty?

Replacing an opaque part of the cornea with a clear cadaveric one.

56
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What are the indications for keratoplasty?

Optical, therapeutic, structural, and cosmetic.