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Cornea Flashcards

1
Q

what is the refacting power of the cornea

A

40D, avg ref power is 60D

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2
Q

what are the horiz and vert dimensions of the cornea

A
  1. 6mm vert

11. 6 horiz

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3
Q

what is the central thickness and the peripheral thickness

A

central: 0.53mm
peripheral: 0.7 mm

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4
Q

what can disruption to the basement membrane lead to

A

recurrent corneal erosisions

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5
Q

how many layers are in the epithelium

A

5-7 layers

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6
Q

what are the cells in the epi

A

basal columnar cells

wing cells in 2 or 3 rows

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7
Q

what are the basal columnar cells attached by to the basement membrane

A

hemidesomosomes

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8
Q

what is surface area of the outermost cell increased by

A

microplicae and microvilli to facilitate absorption of mucin

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9
Q

does the epi scar from infl? why

A

no bc it can regneerate

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10
Q

what is the basement membrane secteted by

A

basal cells

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11
Q

how long does the basement membrane take to regenerate

A

6-8 weeks

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12
Q

what happens when bowmnas is damaged

A

acelular structure does nto regnerate when damaged, scars when disturbed

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13
Q

what is the stroma composed of

A

collagen producing fibroblasts, collagen fibrils, ground substance

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14
Q

why do we have extremem transparency of the cornea

A

criss crossing of lamellae in stroma

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15
Q

what is the ground substance that occupies the space in btwn the lamellae composed of

A

proteoglycans

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16
Q

what is dua’s layer

A

aceullular strong layer in pre-descemet’s cornea

separates last row of keratocytes in most cases

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17
Q

what is descemet’s compoased of

A

fine lattice work of collagen fibrils

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18
Q

why are the epi, endo, and escemets transparent?

why is the stroma transparent?

A

bc of the uniformity of their refractive indices

stroma: bc of the special arrangement of collagen fibrils

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19
Q

what provides sensory innervatino of the cornea

A

ophtlamic division of the trigeminal nerve via the long ciliary nerves

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20
Q

how does the cornea get its blood supply

A

conj episcleral and sceral vessels around corneoscleral limbus

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21
Q

what is the source of neo

A

palisades of vogt: contain blood vessels and lymphatics

-denate conj projection into cornea

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22
Q

what contributes to loss of corneal clarity

A
  1. corneal edema (ep edema, stromal edema)
    - scatters light is hydrated 5% more
  2. scarring
  3. corneal neo
  4. corneal injury
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23
Q

what is medicamentosa

A

medicine in eye causes corneal ep

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24
Q

what are some causes of ep edema

A
  1. PMMA contact lense
  2. epi defects
  3. swimming
  4. medicamentosa
  5. angle closure glauc
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25
will ep edema decrease va
yes. significant, PAINFUL halos around light, foggy vision spectacle blur w/ hard and gas perm lens
26
is stromal edema significant
only a mild reduction va and mild glare advanced stromal edema=ep edema *painless*
27
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
28
which layers scar and which do not
scar: bowman's layer and stroma doesnt: epi, descements, endo
29
how to grade scars
nebular: faint macular: translucent leukoma: opaque
30
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
31
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) ```
32
what are the 5 symptoms to think of when evaluating corneal insult
1. pain or discomfort 2. halos 3. impairment of va 4. photophobia 5. lacrimation
33
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
34
why do halos occur
due to diffraction of light as a result of ep edema
35
why does impairment of va occur
loss of central transparency | increaed tearing causes water ot leak into the wound
36
what is photophobia caused by
abnormal strong light induced miosis to an inflamed iris and ciliary spasm
37
what is lacrimation caused by
seondary to reflex stimulatin of corneal nerves | -its degree frequently parallels the severity of photophobia
38
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
39
what is a perforation
it means that the cornea has been penetrated all the way through
40
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
41
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
42
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
43
what is the ultimate event in ulcer formation
enzymatic destruction of the macromolec that make up the collagen of the cornea
44
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
45
what is debridement
removement of damaged dissue | debridement scraping of the ep and basement membrane can improve adhesion after healing
46
when to use anterior stromal puncture
if recurrent erosion in same protion of off-axis cornea
47
what to use on patients with recalcitrant recurrent erosions
``` pthototherapeutic keratectomy (PTK) -excimer laser to ant 2-4microns of bowman's membrane ```
48
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
49
after fb is removed, how to treat
like a corneal abrasion
50
what is fleischer's ring
at the base of a cone in keratoconus
51
what is ferry line
around a filtering bleb (glauc surgery)
52
what is stocker's line
at the head of a ptergygium
53
what is coat's ring
seen after an iron fb is removed
54
what are the 3 most common corneal dystrophies
1. keratoconus 2. fuch's ep-endo dystrophy 3. ep basement membrane disorders
55
what is munson's sign
lower lid looks convex on down gaze
56
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
57
when is keratoconus classified as mild, moderate, and severe
mild K < 48D moderate K48-54D severe K > 54D
58
what are the different types of cones
nipple small: (6mm, may involve over 70% of the cornea
59
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
60
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
61
what does fuch's dystrophy lead to
stromal and epi edema | epi edema can produce subep bullae which can cause pain
62
what instruement is used to measure corneal endo cell density
specular microscope
63
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
64
what is the earliest sign of fuch's
guttata which changes the endo layer which decreases its ability to function as a pump
65
what is the best way to view stroma edema? ep edema?
indirect ill to view the stria | ep=scerotic scatter
66
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
67
when does vision become sig affected in fuch's
when ep edema develops
68
what should you not use to lower iop in fuch's
carbonic anhydrase inhibitors bc it may compromise endo further
69
what are the most common corneal dystrophies
ep basement membrane dystrophy | aka cogan's, fingerprint, map-dot
70
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
71
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
72
what are fingerprints | how are they best seen
basement membrane projecting up and trapping the anteriorly migrating cells best seen in retro
73
what are map-like changes related to
multilaminar thickening of basment membrane w/ extension of the aberrant membrane into overlying ep
74
what are blebs
localized mounds of fibrillogranular protein btwn bowman's layer and the ep basement membrane indenting the basal ep
75
which defects can you see w/ positive staining (ep layer dystrophies)
maps, microcysts when they break through | fingerprint is combo neg and pos
76
why do phenothiazines (antipsychotics) leave fine yellow borwn white deposits in interpalpebral deep stroma
action related to blockage of dopamine receptors in the CNS
77
what does chrysiasis leave on the cornea
yellow deposits in post stroma and descemet's | -effects reversed when drug is stopped
78
what is the corneal affect in retinoids (acutane
fine round sub ep opacities in the central and peripheral cornea

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