External Eye and Cornea Flashcards
What is the refractive power of the cornea?
43D
What is the diameter of the cornea in a) an adult b) a newborn?
a) 10-13mm
b) 9.5-10.5mm
What is the thickness of the cornea a) centrally b) peripherally?
a) 535mcm b) 660mcm
Is the cornea vascular?
no
Where does the cornea get nutrition from?
aqueous humour and tear film
Which nerves supply the cornea?
Long ciliary nerves - from V1
How many layers does the cornea have?
5
Name the layers of the cornea from outermost to innermost.
epithelium Bowman's layer Stroma Descemet's membrane endothelium
Which corneal layer is the principal barrier to topical eye drops?
Epithelium
Lipid soluble drugs pass easily
Does the epithelium have regenerative potential?
yes- contains limbal stem cells
Which layer of the cornea is this:
thickest layer
contains keratinocytes and collagen fibrils
no regenerative power
increased pH increases absorption across this layer
stroma
Do acids or alkaline chemicals cause more damage to the eye?
alkaline- increasing pH causes increased absorption of chemicals across the stroma
Which elastic layer of the cornea contains type 4 collagen fibres?
Descemet’s membrane
What is the function of the corneal endothelium?
pumps fluid out of the stroma to maintain its transparency
contact lens wearer, unilateral acute pain, redness, photophobia and decreased VA with circumcorneal injection and discharge
bacterial keratitis
which bugs most commonly cause bacterial keratitis?
pseudomonas, staph aureus
which organisms cause a bacterial keratitis that is more likely to spread and infect the whole globe?
Neisseria gonorrhoea
Haemophilus influenzae
Which class of abx should be used in bacterial keratitis?
fluoroquinolones (-floxacin)
patient ran into a tree branch, feathery branching infiltrate on cornea, aspergillus cultured
filamentous fungal keratitis
immunocompromised patient,small ulcer with expanding infiltrate in collar stud formation
candida fungal keratitis
What treatment is given for filamentous fungal keratitis?
natamycin drops
What treatment is given for candida keratitis?
amphotericin B or voriconazole
Patient been swimming with contact lenses in. Eye pain out of proportion with clinical signs, photophobia and blurred vision. Ring shaped stromal infiltrates and perineural infiltrates.
Acathamoeba keratitis
What is the management for acanthamoeba keratitis?
stop contact lens wear
topical polyhexamethylene biguanide or chlorhexadine
Blepharo conjunctivitis, pain, blurred vision, lacrimation, foreign body sensation, photophobia. Dendritic ulcer seen with fluorescein. Dendrite margins stain well with rose Bengal.
Herpes simplex keratitis
Which HSV is the most common cause of viral keratitis?
HSV 1
What is the treatment for herpes simplex keratitis?
topical acyclovir
Dermatomal rash, Hutchinson’s sign. Keratitis with psuedodendrites- stain well with rose Bengal.
herpes zoster ophthalmicus
What is the treatment for herpes zoster ophthalmicus?
oral acyclovir 800mg 5 times/day
topical lubricants
Pain, photophobia, decreased VA, feathery midstromal scarring and neovascularisation.
interstitial keratitis
Causes of interstitial keratitis?
syphilis lyme disease HSV HZV Cogan syndrome
Interstitial keratitis, notched teeth and sensorineural deafness
Hutchinson’s triad of congenital syphilis
interstitial keratitis, sensorineural hearing loss, vertigo and tinnitus
Cogan Syndrome
degeneration of corneal epithelium, foreign body sensation, mobile comma shaped epithelial strands
filamentory keratitis
due to tear film changes
conditions associated with filamentary keratitis
sicca syndrome
Sjogren’s syndrome
contact lenses
Peripheral corneal inflammation. Subepithelial infiltrates separated from the limbus by the clear zone. Staph infection
marginal keratitis
what type of hypersensitivity reaction is seen in marginal keratitis?
type III