Lecture 2: 11/10 Flashcards
what is the groove structure between the junction of the cornea and sclera?
called a sulcus (external and internal parts)
what is unique about the external sulcus of the cornea?
can’t see it because that groove is filled over with conjunctiva
what important structure is in the inside sulcus of the cornea?
trabecular meshwork
what is the trabecular meshwork important for?
for drainage of the fluid in the anterior portion of the eye
central cornea thickness
0.50 - 0.70 mm
peripheral cornea thickness
0.74 - 1.10 mm
average thickness of the cornea
0.56 mm
anatomical measurement of cornea is
direct, postmortem on dead cornea
physiological measurement of the cornea is
thickness in living human using ultrasonic device
which thickness measurement is more representative: anatomical or physiological?
physiological is better because the cornea is functioning and living, post-mortem the cornea starts to swell
to measure corneal thickness, what device can be used?
pachometer
anterior cornea values for horizontal and vertical diameter
horizontal: 11.7 mm
vertical: 10.6 mm
posterior cornea values for horizontal and vertical diameter
horizontal: 11.7 mm
vertical: 11.7 mm
3 possible reasons for the elliptical shape of the anterior cornea
- embryology
- blinking
- eyelids
what is a micro cornea and what can cause it?
when cornea is smaller than normal and horizontal diameter is less than 11mm
(result of embryology)
what is a meglocornea and what can cause it?
when horizontal diameter is greater than 12.5 mm, most likely the result of congenital glaucoma
congenital glaucoma is
when you are born with high intraocular pressure, can be caused by ciliary body and iris blocking off trabecular meshwork
treatment of congenital glaucoma is
surgery which can take care of anatomical blockage to open trabecular meshwork and allow drainage
central anterior radius curvature cornea
7.8 mm
posterior radius of curvature cornea
6.5 mm
edema of the cornea results in
changes in the anterior radius of curvature because collagen fibers aren’t elastic enough to give and cornea tends to flatten
what is the base of cornea anatomical measurement
hypothetical line from one end of the cornea to the other
how do you measure the vault of the cornea?
take measurement from base of cornea hypothetical line to anterior surface of the cornea
vault value for the cornea is
2.6mm
temperature of the cornea is usually
90 degrees
why does the cornea have a cooler temperature than the core of the body?
- tear evaporation
- it is an external surface
- avascular
davson experiment results:
corneas in 27C became cloudy, when placed back in 37C, they cleared up again
conclusion of the davson experiment
turning down the temperature slowed down metabolism and the cornea swelled and took on water, pumps slowed down, but speed back up with temperature increase
the dehydrated state of the cornea is called
deturgescence
describe the process of cornea edema
collagen fibers interrupted by the water which disturbs fiber precise arrangement leading to cornea opaqueness from pump slowing
3 things that can cause cornea edema
- oxygen deprivation
- trauma
- IOP
average IOP values
15-20 mmHg
dilated patients can have increased pressure up to what values?
40-50 mmHg
2 aspects of the cornea are
central (cornea proper) and limbus (transition zone to sclera)
list of the 5 layers of the cornea proper, from anterior to posterior
- anterior epithelium
- bowman’s membrane
- stroma
- descement’s membrane
- endothelium
width of the limbus transition zone
1.5-2.0mm wide
purpose of the anterior epithelium
to present smooth surface for that refracting element of the eye
thickness of the anterior epithelium is
5-6 cells thick
histology of the anterior epithelium
- wet
- stratified (3 types of cells in this layer)
- squamous (anterior surface cells are flat and plate like)
list 3 cell types found in anterior epithelium
- basal cells
- wing cells
- surface cells
describe the anterior epithelium cell type: basal cells and their attachments
most interior, attached to basement membrane via hemi-desmosomes (not a strong attachment)
why is the basal cell layer important?
it is the germinal layer for epithelial cell, highest rate of mitosis in the cornea, cells are formed here and work their way up to the surface
wing cells appearance and layer details
cells that are starting to flatten out, contain the next 3 layers of cells
apex and base of wing cells are
- convex on top surface
- concave on bottom surface
purpose of wing cells
help ad mass to anterior epithelium
surface cells have low many cell layers and what kind of histology
1-2 layers
-plate like, squamous, pretty flat and wide
surface cells have projections called
microplicae
on surface cells, what are the microplicae projections useful for?
thought to have a base for tears to attach and spread out
surface cells are attached via
demosomes
a lot stronger
whole anterior epithelium of the cornea is how thick?
50-100 microns
anterior epithelium represents what percentage of the thickness of the cornea?
10%
