Cornea Flashcards
How is the cornea different to the sclera?
transparent
Describe the refraction power of the cornea?
HIGHEST REFRACTION POWER IN THE EYE: 40D
What is the average diameter of the cornea in the adult and newborn?
10-13MM IN ADULTS AND 9.5-10.5MM IN NEWBORNS
What is the thickness of the cornea?
535um
Where does the cornea receive its nutrients from?
anteriorly - tear film
posteriorly - aqueous humour
Describe the sensory supply of the cornea?
CNV1 via long ciliary nerve
What are the layers of the cornea?
Epithelial layer Bowman layer Stromal layer Descemet membrane Endothelium
Describe the epithelial layer of the cornea
STRATIFIED NONKERATINIZED SQUAMOUS EPITHELIUM
high regenerative potential to injury due to the presence of limbal epithelial stem cells
Where are palisades of Vogt more prominent?
superior and inferior limbus
Describe the bowman layer
Avascular layer (no regeneration potential) that contains collagen fibres and terminates at the limbus
Describe the stromal layer
thickest corneal layer
continuous with the sclera at the limbus
mainly made up of keratocytes and regularly orientated collagen fibrils (type 1 collagen)
it can undergo scarring
no regenerative potential
Describe the descent membrane
An elastic layer containing type IV collage fibres
Describe the endothelium
Function by pumping excess fluid from the stroma to keep the cornea dehydrated to maintain its transparency
Describe bacterial keratitis
common and sight threatening
more common in contact len wearers (soft > rigid), especially in overnight wear / poor hygiene
What are the common organisms in bacterial keratitis?
P aerguinoa (most common cause in contact lens wearers)
S aureus and strep
Describe the features of bacterial keratitis
unilatera sudden-onset pain, redness and photophobia with associated discharge and dVA
purulent / mucopurulent discharge
circumcorneal injection
white infiltrates, epithelial and stromal involvement
anterior chamber cells and hypopyon in severe keratits
What are some complications of bacterial keratitis?
Corneal perforation, esp if:
N gonorrhoea
Corynebacterium diptheriae
H influenzae
How are fungi stained?
sabouraud agar and gram/giemsa stain
How are acanthamoeba stained?
non-nutrient agar with e coli
How is bacterial keratitis investigated?
corneal scrapings for microbio
how is bacterial keratitis managed?
topical broad spec ABx BEFORE lab results return
usually fluoroquinolones (ofloxacin) are typically used
Which patients is fungal keratitis common in?
AIDS
diabetics
immunocompromised
what fungus is more common in those with ocular trauma, esp with plant / tree branch?
filamentous
aspergillum and fusarium
What are specific signs in candidda infections?
small ulcer with an expanding infiltrate in a collar stud formation
What are specific signs in filamentous keratitis?
feathery branching-like infiltrate pattern
what investigations can aid in fungal keratitis?
confocal microscopy
how is fungal keratitis managed?
natamycin drops for proven filamentous infection
variconazole or amphotericin B drops for proven candida
What is a risk factor for acanthamoeba keratitis?
improper lens hygiene (showering / swimming in contact lenses)
What are the features of acanthamoeba keratitis?
pain out of proportion with clinical signs,
photophobia
blurred vision
later disease: perineural infiltrates and ring shaped strmal infiltrates can be seen
what are the investigations for acanthamoeba?
corneal scraping and / or confocal microscopy to identify the presence of amoebic cysts
how is acanthamoeba keratitis treated?
topical polyhexamethylene biguanide or
chlorhexidine
What additional condition does HSV corneal infection lead to?
blepharoconjunctivitis
where does HSV remain after infection?
in the trigeminal ganglion
Which layers of the cornea can keratitis affect?
epithelial, stromal or endothelial layers of the cornea
Describe the presentation of patients with reactivated HSV keratitis?
pain
dVA
lacrimation
foreign body sensation
What are the signs of HSV keratitis?
superficial punctate keratitis which causes a stellate (star-shaped) erosion which later becomes a dendritic ulcer - seen with fluoroscein
reduced corneal sensation
What is disciform keratitis?
this usually occurs from HSV antigen hypersensitivity, not reactivation
insidious onset
how does disciform keratitis present?
painless dVA
Describe the signs of disciform keratitis
central circular stromal oedema
there is usually mild anterior chamber activity
keratitic precipitates
WESSLEY RING: due to antigen/antibody complex
What are the investigations used in disciform keratitis?
clinical, aided by swabs for PCR or Giemsa staining which shows multinuclear giant cells
Describe the management of disciform keratitis
Epithelial: topical aciclovir, avoid steroids: may lead to geographic ulcer and corneal perforation
Disciform:
oral aciclovir 400g five times a day
avoid topical steroids until epithelium is intact
What virus causes herpes zoster ophthalmicus?
VZV
What is herpes zoster opthalmicus?
shingles in CNV1 dermatome
What are the cutaneous features of HZO?
rash (vesicles / papules)
painful neuralgia
HUTCHINSON SIGN: involvement of tip of nose, indicates a higher likelihood for ocular disease due to the involvement of nasociliary nerve
What are the ophthalmic features of HZO?
epithelial keratitis: pseudo-dendrites are the differentiating features from HSV keratitis, grey, less branching and poor staining with fluoroscein
conjunctivitis
elevated IOP
stromal and disciform keratitis are less common
How is HZO managed?
oral aciclovir 800mg five times a day
amitryptyline for neuropathic pain
What is interstitial keratitis?
describes stromal inflammation +/- neovascularisation
caused by the invasion of microorganism or an immune reaction to a foreign antigen
Describe the features of interstitial keratitis
pain
dVA
photophobia
non-ulcerate stromal keratitis characterised by mid-stromal scarring with ghost vessels
Describe the syphilis aetiology of interstitial keratitis
congenital disease usually causes bilateral corneal involvement, while acquired disease is usually unilateral
Hutchinson triad of congenital syphilis (late feature): interstitial keratitis, notched teeth and sensorineural deafness
treatment: IM benzylpenicillin and topical steroids
describe the aetiology of lyme disease that leads to Interstitial keratitis
caused by spirochete bacterial borrelia, which is transmitted to humans via tick bite
causes erythema migrans (BULL’S EYE SKIN RASH), arthralgia, facial palsy, loss of temporal eyebrows and interstitial keratitis
What are some viral causes of interstitial keratitis:
HSV, VZV, EBV
Describe cogan syndrome that leads to interstitial keratitis
autoimmune disorder
interstitial keratitis with sensoriuneural hearing loss, vertigo and tinnitus
complications: polyarteritis nodosa
What is marginal keratitis?
a type of peripheral corneal inflammation due to type III hypersensitivity reaction to staphylococcal exotoxin
associated with rosacea and blepharitis
What are the features of marginal keratitis?
epiphora, redness and photophobia
chronic blepharitis
subepithelial infiltrates separated from the limbus by a clear zone
typically occurs in regions where the eyelid contact the cornea
What is the management of marginal keratitis?
lid hygiene and mild topical steroids
What is peripheral ulcerative keratitis?
group of conditions that leads to peripheral corneal thinning
most common systemic assoc: rheumatoid arthritis
others: Wegners, polyarteritis nodosa, relapsing polychondritis
What are the features of peripheral ulcerative keratitis?
begins peripherally eventually progresses centrally and posteriorly, end stage thin vascular cornea
interpalpebral peripheral corneal stromal thinning with an epithelial defect
episcleritis and / or scleritis may be present
What is the management of ulcerative keratitis?
oral prednisolone +/- systemic immunosuppression, topical steroids by exacerbate thinning
What is ocular rosacea?
acne rosacea leads to facial changes and ocular disease
causes telangiectasia, papules and pustules on the face, facial flushing and rhinophyma
What are the ocular features of ocular rosacea?
dry eyes, redness, epiphora and photophobia
eyelids: telangiectasia and posterior blepharitis
conjunctival hyperaemia
What are the corneal features of ocular rosacea?
marginal keratitis
inferior corneal thinning
superficial erosions
peripheral corneal vascularisation
What is the management of ocualr rosacea?
lid hygiene
topical lubricants
oral tetracyclic
What is filamentary keratitis?
a condition where corneal epithelium degenerates, leading strands / filaments and mucus to adhere to the corneal surface
What are the risk factors for filamentary keratitis?
dry eye syndrome
corneal epithelium erosions
laser eye surgery
contact lens wear
What are the features of filamentary keratitis?
sensation of foreign body
redness, epiphora and blepharospasm
dry eyes
‘COMMA SHAPED LESION’, MOVE UP AND DOWN ON BLINKING AND STAIN WITH ROSE BENGAL
What is keratoconus?
bilateral and asymmetrical condition characterised by progressive central stromal thinning and apical protrusion of the cornea, usually presenting in early adulthood
What are the features of filamentary keratitis?
irregular astigmatism
lower eyelid protrusion on downgaze (munson sign)
vertical striations in the stroma, seen on slit lamp (vogt striae)
iron deposit often within the epithelium around the base of the cone (felischer ring)
‘oil drop’ reflex on ophthalmoscopy
‘scissoring’ reflex on retinoscopy
What is a complication of keratoconus?
acute hydrops
- tear in descemet membrane leading to corneal oedema
- presentation: dVA pain and photophobia
What investigations are used in keratoconus?
KERATOMETRY: GRADING OF KERATOCONUS INTO MILD, MODERATE AND SEVERE: <48D = MILD AND >54D = SEVERE
VIDEO KERATOGRAPHY (CORNEAL TOPOGRAPHY): ESSENTIAL TO PICK UP EARLY KERATOCONUS
- VERY USEFUL FOR MONITORING AND HAS REPLACED KERATOMETRY
- IT SHOWS AN ASYMMETERICAL BOW-TIE PATTERN IN EARLY DISEASE AND PROGRESSES INTO A STEEP CONE THAT IS DISPLACED OF THE VISUAL AXIS
How is keratoconus managed?
MILD: SPECTACLE CORRECTION
MODERATE: RIGID / HARD CONTACT LENSES OR CORNEAL COLLAGEN CROSS-LINKING USING RIBOFLAVIN DROPS AND ULTRAVIOLENT-A
SEVERE: PENETRATING OR DEEP ANTERIOR LAMELLAR KERATOPLASTY
LASIK IS GENERALLY CONTRAINDICATED
What is microophthalmia?
CONDITION IN WHICH THE WHOLE EYE IS SMALLER THAT THE AVERAGE BY AT LEAST TWO STANDARD DEVIATIONS
What is simple microphthalmos?
BILATERAL INVOLVEMENT; THE EYE IS SMALL BUT NORMAL
ASSOCIATED WITH ANGLE CLOSURE GLAUCOMA, UVEAL EFFUSION SYNDROME, HYPERMETROPIA, AMBYLOPIA AND STRABISMUS
What is complex micropthalmos?
A SMALL EYE ASSOCIATED WITH OTHER ABNORMALITIES INCLUDING ORBITAL CYSTS OR COLOBOMAS (HOLE IN THE OCULAR STRUCTURE)
ASSOCIATED WITH FETAL ALCOHOL SYNDROME AND INTRAUTERINE INFECTIONS
What is wilson disease?
AN AUTO RECESSIVE GENETIC DISORDER CAUSING DEPOSITION OF COPPER IN THE BODY
THE MOST COMMON AREAS AFFECTED ARE LIVER, BRAIN AND EYES
Describe the features of wilson disease?
HEPATIC CIRRHOSIS LEADING TO PORTAL HYPERTENSION, ASCITES, VARICES AND HEPATIC ENCEPHALOPATHY
MOVEMENT DISORDERS AND ATAXIA
KAYSER-FLEISCHER RING: COPPER DEPOSITION IN DESCEMET’S MEMBRANE
ANTERIOR SUBSCAPULAR SUNFLOWER CATARACTS
What is band keratopathy?
it’s a sign due to calcium deposition in the Bowman’s layer
Describe the aetiology of band keratopathy
IDIOPATHIC
OLD AGE
HYPERCALCAEMIA AND HYPERPHOSPHATAEMIA
SILICONE OIL
CHRONIC AVTERIOR UVEITIS
What are the features of band keratopathy?
OFTEN ASYMPTOMATIC
INTERPLPEBRAL PERIPHERAL ZONE CALCIFICATION (BAND-LIKE CHALKY PLAQUE) WITH A CLEAR ZONE SEPARATING IT FROM THE LIMBUS
How is band keratopathy managed?
TREAT UNDERLYIN CAUSE
CHELATION WITH EDTA
What are corneal dystrophies?
a group of progressive hereditary disorders that cause corneal opacification and can lead to visual impairment
can be classified as anterior (predominantly affecting the epithelium), stromal or endothelial
What is cogan dystrophy (map-dot-fingerprint dystrophy)?
MOST COMMON EPITHELIAL DYSTROPHY
SPORADIC OR AD INHERITENCE
What are the features of cogan dystrophy?
ONSET IS IN SECOND DECADE WITH BILATERAL RECURRENT CORNEAL EROSIONS (RECURRENT PAIN, PHOTOPHOBIA AND EPIPHORA)
SIGNS ARE BEST SSEN ON RETROILLUMINATION SLIT LAMP
- MAP: SUBEPITHELIAL GEOGRAPHIC OPACITIES
- DOT: INTRAEPITHELIAL MICROCYSTS
- FINGERPRINT: SUBEPITHELIAL RIDGES
What is Reis-buckler dystrophy?
An AD condition that occurs as a result of the replacement of Bowman’s layer with connective tissue
What are the features of reis-buckler dystrophy?
PRESENTS WITH RECURRENT CORNEAL EROSIONS IN CHILDHOOD
BECOME LESS PAINFUL WITH AGE DUE TO DECREASED CORNEAL SENSATION
EXAMINATION MAY REVEAL SUBEPITHELIAL CLOUDY OPACITIES CENTRALLY
What are the three types of stromal dystrophies?
LATTICE DYSTROPHY
GRANULAR DYSTROPHY
MACULAR DYSTROPHY
What are the features of macular stromal dystrophy?
BILATERAL VISUAL LOSS IN FIRST DECADE
GREY, POORLY DEMARCATED OPACITIES IN THE STROMA
Describe macular dystrophy
MARILYN MONROE ALWAYS:
- MUCOPOLYSACCHARIDE ACCUMULATION IN STROMA
- MACULAR DYSTROPHY
- ALCIAN BLUE USED TO STAIN MUCOPOLYSACCHARIDES
Describe granular dystrophy
Gets Her Men:
GRANULAR DYSTROPHY
HYALINE DEPOSITS IN THE STROMA
MASSON TRICHOME IS USED TO STAIN HYALINE
Describe the features of granular dystrophy
DVA AND RECURRENT CORNEAL EROSIONS
BREADCRUMB-LIKE OPACITIES IN AN OTHERWISE HEALTHY STROMA
Describe lattice dystrophy
LA COUNTY
- LATTICE DYSTROPHY
- AMYLIOD DEPOSITS IN THE STROMA
- CONGO RED IS USED TO STAIN AMYLOID (GREEN BIREFRINGENCE IN POLZARIXED LIGHT)
Describe the features of lattice dystrophy
DVA AND RECURRENT CORNEAL EROSIONS
REDUCED CORNEAL SENSATION
EXAMINATION SHOWS ANTERIOR GLOSSY STROMAL DOTS, AFFECTING THE CENTRE, FORM TOUGH TO FORM FINE FILAMENTOUS LINES
Describe fuchs endothelial dystrophies
MOST COMMON CORNEAL DYSTROPHY
INHERITENCE IS SPORADIC OR AD
MORE COMMON IN ELDERLY FEMALES
DUE TO FAILURE OF SODIUM / POTASSIUM PUMP LEADING TO ACCUMULATION OF FLUID IN THE CORNEA WHICH LEADS TO ENDOTHELIAL CELLS LOSS
What are the features of fuchs’ corneal dystrophy?
BLURRY VISION WORSE IN MORNING
SPECULAR MICROSCOPY MAY SHOW CORNEAL GUTTATA (‘BEATEN METAL’ APPEARANCE) AND LOW ENDOTHELIAL CELL COUNTS
PACHYMETRY MAY SHOW INCREASED CENTRAL CORNEAL THICKNESS
