Phsiologic Aging Changes Of The Cornea Flashcards
CCT at birth
Full adult thickness
Horistonal diamater of cornea at birth
10mm, 90% of the adult value
Axial length of cornea at birht
Just over 2/3 of adults
At birth, the cornea occupies _____ of eye surface
25%
15% in adults
Corneal aquires adult size at ____ years
3
Sclera gorws until ______ years
10 to 12
What does the sclera growing until 10 or 12 account for
Normal hyperopia among children.
When do most eyes become emmetropic
6 to 8 years
Ag related changes in the cornea and vision
Not detrimental to vision
When will vision be affected with corneal aging changes
If change is central cornea and affects the transparency of the tissue
Where do most age related corneal changes happen
At the periphery
Corneal sensitivity and aging
Decreases
Light scatter and corneal aging
Increases
Corneal curvature and aging
Flattening of the cornea (vertically) causing ATR astigmatism
Bowmans membrane and corneal aging
Stippling
Descemet’s membrane and corneal aging
Thickening
The most common aging change in the cornea
Corneal arcus
Annular yellow-white deposit located within the peripheral stroma
Corneal arcus
What is corneal arcus separated from the limbus by
A zone of clear cornea
What are the deposits in corneal arcus
Cholesterol or cholesterol esters
What does corneal arcus result from
Age or elevated blood cholesterol levels
Arcus extending over time
Can extend anteriorly over time to bowmans layer or into the central cornea
Clinical significance in those with corneal arcus
Non in elderly persons, but in those under age 40, hyperlipidemia should be suspected
What race is corneal arcus more common and pronounced
Blacks
What percent of population has corneal arcus by age 50
50%
What percent of population has corneal arcus by age 80
100%
Is corneal arcus unilateral or bilateral
Bilateral
What layer of the cornea can corneal arcus effect
Bowmans
What should you consider in someone with corneal arcus
Cardiovascular risk factors
Corneal epithelium and aging
Alterations to cellular transmembrane receptors (integrins)
- these form bridges from cell to cell and from cell to ECM
- link cytoskeleton to ECM
- fibronectin
- change results in reduction in the adhesion molecules necessary for intercellular junction construction
Los of intracellular junctions in the corneal epithelium
Causes a breakdown in the barrier function of hte corneal epithelium
Decreased keratocyte density in the corneal epithelium
Can adversely affect wound healing and colllagen fibril degradation produces spaces that can disrupt transparency and create opacities
Iron deposits in epithelial cell cytoplasm, mroe concentrated in basal cells, produce a horizaotnal pigmented line
Hudson-stahli line
Where is a Hudson-Stahli line evident
At the level of the lower lid margin
When does Hudson-Stahli line fade
Usually present between 50 and 70, fades after that
What should you consider with someone who has Hudson-Stahli lines
Hydrochloroquine use
Degeneration of bowmans layer
Lima girdle of Vogt
Where is the limbs girls of vogt found and what color is it
This yellowish white opacity is located at the 3 and 9 o clock positions
Limbal girdle of Vogt type I
A clear interval separating the opacity from the limbus
In type II this is not seen
The area around the Lima girdle of Vogt
May include degeneration of the anterior stroma, calcium deposits, and hypertrophy of the overlying epithelium
Changes in descemets membtane with age
Increases in thickness
Hassall-henle boidies increase in the periphery
Small round peripheral endothelial indentations produced by thickening of descemets membrnae
Hassall-henle bodies
Appear as corneal guttata (peripheral_
Hassall-Hanle bodies
What must you rule out in Hassan-Henle bodies
Fuch’s
What can Hassal-Henle bodies cause
Atypical arcus
When does endothelial cell density decrease
With cell loss
What is a normal endothelial cell density
4000 cells/mm2
Polymegathism
Greater than normal variation in size of the corneal endothelial cells
Pleomorphism
Increases variability in size and shape
Pigment deposits on the posterior cornea with a vertical orientation
Krukenberg’s spindle
What do you need to be careful with the a Krukenberg’s spindle
High IOP
A decrease in corneal sensitivity corresponds to a loss of corneal ____with age
Nerves
Changes in refractive components and in eye size must be well-balanced during childhood growth to allow for
Emmetropization
When does refractive error result
Eye is too short or too long or if the cornea is too flat or too steep
What is refractive error typically due to
Eye length
____ may be a factor when emmetropization does not occur
Scleral tissue
When does myopia usually develop
8-14 years
What is myopia most often cause by
The lengthening of posterior eye, containing the vitreous
Scleral connective tissue components and visual environment
Can change in response to changes in the visual environment
Poor image quality on the retina and scleral tissue components
Poor image quality on the retina can elicit a signal to scleral tissue components to strengthen or weaken in an attempt to move the retina to the best location for a clear image
Sunlight and myopia
- altered light cycles cause eye growth and myopia in animal studies
- a reduced risk of myopia with increased outdoor activity
- reduction in myopia with latitudes near equator
- either do to light intensity or greater object distances
What does scleral remodeling cause
Axial lengthening that occurs in myopia; existing scleral tissue is weakened and thins. In progressive myopia, collagen is degraded, the production of newcollagen is reduced, and matric proteoglycans are lost
Changes of the sclera during myopia development
Changes int he ECM but an additional piece of the puzzle may be the role played by scleral fibroblasts; if stimulated to become myofibrils. They can produce biochemical signals leading to changes in collagen production and degradation of tissue
The progression of myopia caused by axial elongation in a highly myopic eye often causes scleral thinning, particularly at the posterior pole where the collagen fibril diamtere and the bundle size are reduced. As the sclera thins, the tissue can bulge outward causing this
Scleral ectasa
Yellow sclera with age
Fatty deposits
Scleral collagen and elastic fibers in aging sclera
Degenerate
Fibers of the lamina cribrosa and age
Become stiffer and less resilient
-may make the nerve fibers passing through the openings more susceptible to injury, contributing to an increased susceptibility to glaucomatous damage.
