The Cornea Flashcards
describe the functional anatomy of the cornea
- transmission of light:
-optical transparency
-major refractive medium of the eye - defense: barrier between eye and environment
describe cornea microscopic anatomy
- (precorneal tear film) not really part of cornea but SO IMPORTANT
- surface epithelium
-surface epi has no basement membrane! - stroma: collagen and protein, 90% of thickness of cornea
-richly innervated, especially superficially
-superficially corneal ulcers are PAINFUL
-optically transparent for light transmission!! (avascular, non-pigmented, relatively dehydrated, regular collagen fibril arrangement) - Descemet’s membrane: basement membrane of corneal endothelium
- endothelium: innermost layer
-single layer of cuboidal cells (technically epithelium but on inside)
-monolayer squamous epithelial layer lining the posterior/inner corneal surface
-post mitotic!! non-regenerative!!
-maintains corneal dehydration
describe the surface epithelium
- surface epi has no basement membrane!
- refraction: tear film smoothens refractive surface of epi
- mechanical barrier to fluid imbibtion by stroma; corneal edema develops in areas of corneal ulceration (epi loss or absence)
- lipophilic/hydrophobic; does NOT retain fluorescein, barrier to drug passage
describe the stroma
- richly innervated, especially superficially
- superficially corneal ulcers are PAINFUL
- optically transparent for light transmission!! (avascular, non-pigmented, relatively dehydrated, regular collagen fibril arrangement)
describe corneal deturgescence
- corneal stroma is maintained in relatively dehydrated state (despite being bathed in tears and aqueous humor = deturgescence
- how deturgescence
-evaporation and salinity of tears: hypertonicity is minor contribution but draws some fluid out
-EPITHELIUM: mechanical, hydrophobic barrier to fluid imbibition
-ENDOTHELIUM: mechanical hydrophobic barrier AND sodium potassium ATPase pumps actively pump fluid out into anterior chamber
-avascularity
describe the endothelium
-monolayer squamous (heaxgon shaped) epithelial layer lining the posterior/inner corneal surface
-post mitotic!! non-regenerative!!
-maintains corneal dehydration
describe corneal wound healing
epithelial: relatively easy
stroma: complicated and takes a lot!
-neutrophil invasion
-wound margin karatocyte transform into fibroblasts that invade wound
-collagen and GAG synth, reorganization, return of tensile strength (steps not important!!)
-process occurs through/enhanced by angiogenesis (vascularization)= IMPORTANT
describe corneal eval/exam
- retroillumination
- diffuse direct and transillumination (+/- mag)
- focused slit beam or small spot:
-project obliquely to form optic cross section
-parallel-piped of light at changes of media: purkinje images
-allows lesion localization
-ALLOWS lesions DEPTH determination
–front beam of slit follows cornea; if lose thickness of cornea, front beam gets closer to back beam and can gauge depth
describe diagnostic tests for the cornea
- schirmer tear test: and tear film wuality tests
-intimate relationship of tear film and cornea/corneal health - flueorescein (rose bnengal) stain: epi defects/mucin deficiency
- cytology: if/for infiltrate
- culture: if/for suspected infectious
- response to therapy!
describe corneal opacities/colors
- red: vessels, hemorrhage
- white:
-sparkly/chunky: deposit
-wispy: fibrosis (scar) - yellowish-white: cellular infiltrate
- blue(ish) white: edema
- tan: keratic precipitates: uveitis indicator
- brown/black: pigment, foreign body, sequestrum
describe corneal vascularization
if you have corneal vascularization, you have chronic corneal irritation (keratitis) of some cause
superficial: extension of conjunctiva (FYI)
1. vessels cross limbus
2. tends to be dendritic
3. indicates ocular surface disease
deep: extension of scleral vessels? (FYI)
1. deeper in stroma
2. brush border (hedgerow)
3. indicates intraocular disease (uveitis, glaucoma)
hemorrhage:
1. intra-corneal/stromal
2. indicates vascularization
describe corneal deposits
- lipid (cholesterol) or mineral (Ca2+)
- crystalline/opalescent (lipid) or chalky/chunky (calcium)
- usually well-delineated edges
describe corneal scars
- wispy grey to dense white
- inactive with usually quiet eye
- history supports
describe corneal cellular infiltrate
- yellow-white creamy/soft to dense white
- inflammatory cells:
-infection and cells responding
-sterile: immune-mediated - neoplastic cells
- may be associated with stromal loss or thickening
- cytology +/- culture indicated
active! cells present that shouldn’t be!
-context help differentiate from scar
describe corneal edema
blue opacity!
- hazy grey to dense blue with severity
+/- cobblestone appearance - thickens cornea (visible with purkinje images) +/- forms bullae
- indicates:
-epithelial defect: fluorescein stain in for ulcer
-endothelial defect/dysfunction (itis, glaucoma, dystrophy, or degeneration)
-corneal vascularization
