L8 Cornea Anatomy, Physiology, and Imaging

____ with the tear film makes up 2/3 of total refractive power of the eye

cornea

t/f the cornea is a key barrier against infection and damage to deeper ocular structures

true

the cornea is ___-____ mm horizontally ~__mm smaller vertically

11.5-12mm, 1mm

the cornea's anterior refractive power is ___ to ___

43 to 43.50

cornea is ___ shape

prolate

cornea is _____ centrally and _____ peripherally

steeper, flatter

corneal epithelium has ___ junctions between superficial cells

tight

apical projections increase ___ ___ contact

surface area

basal cells are the most

posterior

basal cells have ___ junctions and ____ making it slighly more permeable

gap and zonulae adherens

basal cells are the only epithelial cell capable of ____

mitosis

basal cells are adherent to basement membrane via _____

hemidesmosomes

corneal epithelium complete turnover every ___ -___ days

7-10

basement membranes require _ weeks to reconstruct and heal. during this time overlying epithelium has ___ __ during healing

6, unstable bonds

t/f epithelial stem cells localized to limbal basal epithelium

true

limbal stem cells in the epithelium migrate ___ and ____ to differentiate

apically and centrally

the corneal stroma have fibers aligned in parallel fashion within each ____

lamella

the corneal crystallins within the corneal stroma serve the purpose

reduces forward light scatter

the corneal stroma gives _____ strength

mechanical

t/f peripheral stroma is thicker than central stroma

true

keratocytes in the stroma make up ___% of the volume

10

is the corneal stroma rigid? yes or no

yes

_____ is more rigid compared to the posterior

anterior

the corneal stroma is innervated via

nasociliary branch of V1

cornea is steeper ____ and flatter ____

centrally, peripherally

cornea is thinner ____ and thicker ____

centrally, peripherally

____is a monolayer of cell that flatten to 4mm in thickness in adulthood

endothelium

endothelium contains ___ and ___ junctions

gap and tight

endothelium layer functions to

maintain stromal deturgscence or regulate fluid so there it little to none within the stroma

________cells/mm2 = risk for corneal edema

<500

the physiology of endothelium consists of ___ and ___ pump sites, intracellular ____ anhydrase pathway

Na and K, carbonic

metabolic disorders, hypoxia, toxins, injury, alteration in pH and glaucoma are stressors that causes changed to

endothelium and cell density loss

from __ to ___ hours the cells at edge of defect migrate and spread to cover the defect. fibronectin and laminin protein play a role

minute and 5-6 hours

___ to ___ hours mitosis begins so with basal cells, transient amplifying cells and limbal stem cells

24-30

persistent epithelial defects during wound healing can occur such as damage to ___ nerves which reduces growth factor and substance P AND damage to ___ cells. matrix metalloprotease 9 is thought to play a role... loss of sensation?.

corneal, epithelial

what is matrix metalloprotease 9?

enzyme that helps with wound healing and response to wound heal

what happens if there is an over expression of matrix metalloprotease 9?

it will degrade extracellular matrix leading to tissue destruction

stroma's ___ repair to maintain clarity

avascular

in the stroma, keratocytes are activated which enlarge and _____ to injured area

migrate

keratocytes are triggered by functional ____ basement membrane

epithelial

t/f when the stroma is wound healing it results in opacity of the injured area

true (bc keratocytes ?)

within 1-2 of stromal healing, ____ become involved and increases the expression of MMPs

myofibroblasts

during wound healing the endothelium becomes distorted from injuries anteriorly? yes or no

yes

in the endothelium wound healing, surrounding cells ___ and migrates _-_ days after injury

enlarge, 1-3

____ is the method of measuring the radii of curvature of the two principal corneal meridians by measuring the size of the mire reflections

keratometry

corneal power can be calculated from radius of curvature by

D= 0.3375/r OR r=337.5/D

keratometry is designed to measuere the curvature at a _-_mm diameter within pupil

3-4

list two clinical applications of keratometry

fitting CL

IOL calculations (IOLmaster and lenstar) except refractive sx

___ ____ Is a method of visualizing the power of the corneal surface by videoing anterior corneal images + computer processing giving u a map of corneal surface power distribution

corneal topography

examples of corneal topography (3)

medmont, oculus keratograph, and ziess atlas

corneal topography clincial applications (3)

dx/ manage pathology

evaluating vision (RK/PRK)

screening for refractive sx

keratometry

corneal topography

placido disk based topography works by

reflection based: measuring rings reflected from anterior corneal surface

for the placido disk topography the close spacing of the mires mean ___ areas of the cornea whereas broad spacing of the mires indicate ___ areas of the cornea

steeper, flatter

what is a limitation of placido disk based topography?

sensitive to disruptions of tear film so perform before drop and IOP testing

grid style reflection corneal topography

____ ____ is point to point reconstruction of specular reflection of color LEDs. it offers increased accuracy and precision

grid style target

___ ___ directly measures both anterior and posterior corneal surfaces to calculate the corneal power

corneal tomography

what are the 3 types of corneal tomography

slit scanning, scheimpflug, and OCT

1. uses series of slit beams at regular intervals to capture light scatter from both surfaces. its able to measure corneal shape and thickness, but less accurate on posterior curvature/power

this describes

slit scanning tomography

oculus pentacam is an example of

slit scanning tomography

___ ____ takes saggittal sections of anterior segment imaged using sheimpflug optics. It increases depth of focus, simulataneous images of the cornea, anterior chamber and lens

sheimpflug tomography

Pentacam HR, sirius, galilei G4 are all examples of

sheimpflug tomography

similar to topography, OCT clinical applications are (4)

dx pathology like keratoconus

evaluating vision (RK/PRK)

screening for refractive sx

cataract sx

in topographic maps, _____ indicate steeper curvature or higher dioptric power whereas _____ are flatter curvature or lower dioptric power

warm, cool

t/f the normal cornea is prolate

true

Topographic maps have a scale where smaller intervals equal more ____ and larger intervals ___ irregularities

noise, mask

1. best overview of the corneal power

2. commonly used for routine screening or diagnostic

3. averages to make smooth map

all describes what kind of map

axial curvature topographic map

this map is the most sensitive meaning it the most accurate for individual points

tangential topographic map

this map shows areas of relative elevation or depression based on best-fit-sphere

elevation display topographic map

pachymetry map shows

corneal thickness

____ is a noninvasive, noncontact imaging using interference pattern of reflected light and relies on reconstructed images from cross sectional (A scans)

anterior segment OCT aka AS-OCT

what are the two types of AS-OCT

time domain and fourier domain

___ ____ is a deeper penetration due to longer wavelength. from a light beam

time domain

___ ___ is higher resolution and faster scans than TD OCT

fourier domain

fourier domain has two types which are

spectral domain and swept source

____ _____ has higher resolution and faster scans than FD OCT, improved signal to noise ratio and more structural detail. it also uses a broadband light source. whereas ___ ___ is similar but with a longer wavelength allowing imaging of anterior chamber to posterior lens and used a swept source laser

spectral domain, swept source

refractive surgery, ectasia disorders, s/p corneal grafts, tear film eval, ocular surface tumors, cataract sx and keratitis are applications of _____ ____

anterior segment OCT

what is one limitation of anterior segment OCT

limited visualization of structures posterior to the iris

___ _____ uses high frequency ultrasound waves and direct contact

high resolution ultrasound biomicroscopy

___ ____ works by echoing from tissues at varying depths are recorded at different time intervals to construct the image

high resolution ultrasound biomicroscopy

ultrasound biomicroscopy is useful for evaluatoin of ocular structures posterior to ___ iris and in areas of _____ corneas

posterior, opaque

ultrasound biomicroscopy clinical applications include (3)

deep ocular masses of iris or CB, gluacoma (acute angle closure) and ocular trauma

___ ____ uses light reflection to allow imaging and analysis of the corneal endothelium

specular microscopy

___ ___ provides pachymetry measurement, endothelial cell density, mean cell area, % of hexagonality or pleomorphism and coefficient of variation

specular microscopy

specular microscopy clinical applications include (3)

corneal dystrophies, corneal transplant sx with eval and cataract extraction w IOL

corneal biomechanical assessment include (2)

ocular response analyzer (ORA)

and

Corvis ST

corneal biomechanical assessment clinical application

associated with glaucoma progression

ocular response analyzer is made up of _____ ___ which is viscoelastic damping of the cornea and ______ ___ which is overall resistance of the cornea

corneal hysteresis, corneal resistance factor

___ ___ is noncontact tonometer that uses air pulse to monitor for corneal deformation response

corvis ST

___ ___ ___ is real time high resolution cellular imaging in 4d layer by layer

in vivo confocal microscopy

in vivo confocal microscopy clinical apps include (5)

DED, neuropathic corneal pain, infectious keratitis, demodex, and corneal deposits and dystrophies