Cornea Flashcards
what is the refacting power of the cornea
40D, avg ref power is 60D
what are the horiz and vert dimensions of the cornea
- 6mm vert
11. 6 horiz
what is the central thickness and the peripheral thickness
central: 0.53mm
peripheral: 0.7 mm
what can disruption to the basement membrane lead to
recurrent corneal erosisions
how many layers are in the epithelium
5-7 layers
what are the cells in the epi
basal columnar cells
wing cells in 2 or 3 rows
what are the basal columnar cells attached by to the basement membrane
hemidesomosomes
what is surface area of the outermost cell increased by
microplicae and microvilli to facilitate absorption of mucin
does the epi scar from infl? why
no bc it can regneerate
what is the basement membrane secteted by
basal cells
how long does the basement membrane take to regenerate
6-8 weeks
what happens when bowmnas is damaged
acelular structure does nto regnerate when damaged, scars when disturbed
what is the stroma composed of
collagen producing fibroblasts, collagen fibrils, ground substance
why do we have extremem transparency of the cornea
criss crossing of lamellae in stroma
what is the ground substance that occupies the space in btwn the lamellae composed of
proteoglycans
what is dua’s layer
aceullular strong layer in pre-descemet’s cornea
separates last row of keratocytes in most cases
what is descemet’s compoased of
fine lattice work of collagen fibrils
why are the epi, endo, and escemets transparent?
why is the stroma transparent?
bc of the uniformity of their refractive indices
stroma: bc of the special arrangement of collagen fibrils
what provides sensory innervatino of the cornea
ophtlamic division of the trigeminal nerve via the long ciliary nerves
how does the cornea get its blood supply
conj episcleral and sceral vessels around corneoscleral limbus
what is the source of neo
palisades of vogt: contain blood vessels and lymphatics
-denate conj projection into cornea
what contributes to loss of corneal clarity
- corneal edema (ep edema, stromal edema)
- scatters light is hydrated 5% more - scarring
- corneal neo
- corneal injury
what is medicamentosa
medicine in eye causes corneal ep
what are some causes of ep edema
- PMMA contact lense
- epi defects
- swimming
- medicamentosa
- angle closure glauc
will ep edema decrease va
yes.
significant, PAINFUL
halos around light, foggy vision
spectacle blur w/ hard and gas perm lens
is stromal edema significant
only a mild reduction va and mild glare
advanced stromal edema=ep edema
painless
what is descemet’s stripping surgery endo keratoplasty (DSAEK)
damaged endo cells replaceed by donor cells for stromal edema
- used if endo is not working
- only descemets and endo is replaced
which layers scar and which do not
scar: bowman’s layer and stroma
doesnt: epi, descements, endo
how to grade scars
nebular: faint
macular: translucent
leukoma: opaque
what are scars a result of
insult to the stomral matrix, activating keratocytes cells to gather at the site of insult and synthesize new collagen
it the pathology is located to the superficial 50-75 microngs, what to use for treatment of scars?
ant third?
phototherapeutic keratectomy (PTK) superficial ant lamella keratoplasty (SALK)
what are the 5 symptoms to think of when evaluating corneal insult
- pain or discomfort
- halos
- impairment of va
- photophobia
- lacrimation
why is pain felt in the cornea
bc the cornea is richy supplied by sensory nerve endings via first division of trigeminal nerve
-has a subep plexus and stromal plexus
why do halos occur
due to diffraction of light as a result of ep edema
why does impairment of va occur
loss of central transparency
increaed tearing causes water ot leak into the wound
what is photophobia caused by
abnormal strong light induced miosis to an inflamed iris and ciliary spasm
what is lacrimation caused by
seondary to reflex stimulatin of corneal nerves
-its degree frequently parallels the severity of photophobia
when the whole ep is denuded such as in a chemical burn, re-ep occurs from migratino of conj cells from…
palisades of vogt’s
what is a perforation
it means that the cornea has been penetrated all the way through
what test can you use to see if there is an abrasion
seidel test
- see if any aq fluid leaking out
- with positive seidel can see clear aq running through the yellow stain
what is the diff btwn ulcer and abrasion
ulcer goes beyond bowman’s layer, and surrounded by WBC in the stroma, takes up NaFl and it diffuses into the stroma, lotsa red & purulent dischage, circumlimbal flush *sight threatening condition
abrasion rarely goes beyond bowmans, NaFl stays w/in the wound w/ a small circomescribed halo, usually none or small infiltrate, redness is localized w/ no discharge
infected abrasion can lead to an ulcer
what is a corneal ulcer
a superficial loss of corneal tissue as a result of infection, infl which leads to nerosis
-affects the ep and stroma
what is the ultimate event in ulcer formation
enzymatic destruction of the macromolec that make up the collagen of the cornea
what does anesthetic do to the cornea
slows corneal healing so its easier for the cornea to slough off
-only use it to view cornea if you cannot view it w/o
what is debridement
removement of damaged dissue
debridement scraping of the ep and basement membrane can improve adhesion after healing
when to use anterior stromal puncture
if recurrent erosion in same protion of off-axis cornea
what to use on patients with recalcitrant recurrent erosions
pthototherapeutic keratectomy (PTK) -excimer laser to ant 2-4microns of bowman's membrane
how to treat an abrasion
- antibiotic to protect cornea
- cycloplege w/ any sig abrasion to prevent refelxive iritis
- pressure patch rare if area greater than 10mm
after fb is removed, how to treat
like a corneal abrasion
what is fleischer’s ring
at the base of a cone in keratoconus
what is ferry line
around a filtering bleb (glauc surgery)
what is stocker’s line
at the head of a ptergygium
what is coat’s ring
seen after an iron fb is removed
what are the 3 most common corneal dystrophies
- keratoconus
- fuch’s ep-endo dystrophy
- ep basement membrane disorders
what is munson’s sign
lower lid looks convex on down gaze
what does a sudden break in descemet’s membrane from keratoconus result from?
how to treat?
when does it resolve?
too much stroma edema (corneal hydrops) => aq leaks into stroma
- edema can inc the size of the cornea 2-3x
- accompanied by rapid decrease in vision and pain
- treat w/ cycloplegics and hypertonic sol’n (if breaks into ep) and aq suppressors
- usualy resolves ina couple month s
when is keratoconus classified as mild, moderate, and severe
mild K < 48D
moderate K48-54D
severe K > 54D
what are the different types of cones
nipple small: (6mm, may involve over 70% of the cornea
in the us, cornel collagen cross linking is performed how
epi off, removing the corneal epi and applying riboflavin drops to the eye, then exposed to uva light which produced reactive oxygen molec which forms chem bonds btwn the corneal collagen fibrils
what is fuch’s epi-endo dystrophy
the rate of cell loss of functioning endo cells is accelerated
-below 500 cells/ mm^2 the cornea beings to swell and vision is blurred
what does fuch’s dystrophy lead to
stromal and epi edema
epi edema can produce subep bullae which can cause pain
what instruement is used to measure corneal endo cell density
specular microscope
why is the endo important
acts as a barrier to the movement of salt and metabolites into the stroma actively pumping bicarbonate ions out of the stroma and back to the aq humor
what is the earliest sign of fuch’s
guttata which changes the endo layer which decreases its ability to function as a pump
what is the best way to view stroma edema? ep edema?
indirect ill to view the stria
ep=scerotic scatter
why do fuch’s pt have a higher inciddence of glauc
bc whatever causes the problem w/ the endo also tends to cuase probs w/ trab meshwork
when does vision become sig affected in fuch’s
when ep edema develops
what should you not use to lower iop in fuch’s
carbonic anhydrase inhibitors bc it may compromise endo further
what are the most common corneal dystrophies
ep basement membrane dystrophy
aka cogan’s, fingerprint, map-dot
what are the findings in ep layer dystrophy caused from
problems w /the basement membrane
-thickens and it interferes w/ the anchoring of the ep to the stroma
in ep layer dystrophy, the dots are what
intraep microcysts that contain nuclear debris, cytoplasmic debris and lipids
-are prob inverted basal cells which continue to proliferate
what are fingerprints
how are they best seen
basement membrane projecting up and trapping the anteriorly migrating cells
best seen in retro
what are map-like changes related to
multilaminar thickening of basment membrane w/ extension of the aberrant membrane into overlying ep
what are blebs
localized mounds of fibrillogranular protein btwn bowman’s layer and the ep basement membrane indenting the basal ep
which defects can you see w/ positive staining (ep layer dystrophies)
maps, microcysts when they break through
fingerprint is combo neg and pos
why do phenothiazines (antipsychotics) leave fine yellow borwn white deposits in interpalpebral deep stroma
action related to blockage of dopamine receptors in the CNS
what does chrysiasis leave on the cornea
yellow deposits in post stroma and descemet’s
-effects reversed when drug is stopped
what is the corneal affect in retinoids (acutane
fine round sub ep opacities in the central and peripheral cornea
