fall MT Flashcards
(35 cards)
what are the cornea layers–epithelium?
- superficial cells–microvilli/desmosomes, gap junction
- wing cells–desmosomes + gap junctions
- basal cells– desmosomes, hemidesmosomes + gap junction, junctional complexes
- BM= type 4 collagen + laminin
- ** optically smooth, protective against microbial invasion and chemicals, adherent surface for tear film, barrier against influx of water—peripheral langerhand cells
what’s in Bowman’s layer?
- type 1, 3, collage fibers + proteoglycans
- collagen fibers continuous with stroma
- does not regenerate after injury
- maintains epi struction
what’s in the Stroma?
- type 1 collagen= regular arrangement and psacing of collagen fibers result in corneal clarity
- glycosaminoglycans= absorb retain water (78%)
- keratocytes= increase GAG
- gives transparency and physical strength with maintence of shape
what’s in descemet’s membrane?
- condensation of Type 4 collage + maninin
- adhere to stroma
- *BM of endo
what’s in the endothelium? what’s average # cells in young adult?
- 3000, 000 cells in normal young adult
- monolayer of endo cells have junctional complexes
- corneal deturgescence via pumping water out of the stroma via ACTIVE transport of ions into ant. chamber
what is the average corneal thickness centrally and peripherally?
overall= 500-550microns @ center, 660 @ periphery ( thicker @ periphery)
- epi= 50 microns
- stroma=thickest @ 450microns
what is the average corneal diameters (aka horizontal visible iris diameter (HVID)?
- horizontal 10-13mm–> average is 11.7mm
- vertical 9-11mm (veritcal is slightly smaller)
- determines the over all diam. of the CL needed
what’s in the Palp conjunctiva vs. the Bulbar conj? what is generally found on the conj?
Palp= several layers of epi cells on substantia propria–adherent to tarsal plate
Bulbar= 6-9 layers of epi cells piled irregularly on the thing basal lamina and stroma= more lookse attached
- conj has goblet cells (for mucin) and accessory lacrimal glands
- blood from ophthalmic artery + facial artery for PALP conj
- blood from anteriod ciliary arteries for BULBAR conj
on the eye lid, what are the various parts and how do they adhere to the eye?
- out skin= loosely adherent to underlying muscle
- inner lid= TIGHTLY adherent to tarsal plate & palp lined
- tarsal plate= 0.75mm thick || densely packed collagen fibers
- meibomian glands= inside tarsal plates
- Glands= Zeiss + Moll @ the lash line
how do you measure the palp aperture height (PAH)? how is this used in CL assessment? Max/min values?
- height between upper and lower lids
- vertical measurement of opening between upper and lower eye lids in RELAXED format.
- ** helps with CL DIAMETER determine**
- larger PAH >/=12mm = larger diameter for max comfort
- smaller PAH </=9mm = smaller diameter
how does lid POSITION affect CL assessment in fit?
- low upper lid that covers a lot of the eye= superior lid attachment in CL
- a high upper lid that does not cover eye= inter-palp lens fit
- high LOWER lid= small lens diameter so it does not scratch the pt’s cornea during blink
- lower lid is a poor candidate for inferior fit RGP’s (RGP BF is bad here)
what is likely to happen in a TIGHT lid vs. a LOOSE lid in lid tension for RGP fit?
- tight lids= pull a lens upwards or squeeze it downward (watermellow seeds effect)
- loose lids= move the lends downward (drops easily)
what is a normal blink rate? and how does it affect CL fit?
- avg. blink rate= 10-15 blinks/min
- determines lens material to be used
what produces lipids in tears? aqueous? mucin? what is total tear film thickness?
- *total tear film thickness=3microns**
- lipids= cholesterol + fat–> secreted via meibomian glands & accessory sebaceous glands of zeiss
- aqueous= electrolyites + proteins–> it’s the bulk of the tear layer and maintains hydration of corneal surface–secreted via glands of Kraus
- mucin=glycoproteins + mucopolysaccharids–> inner most layer that has epithelial mucins that anchor mucins to the microvilli
how does pupil diameter in DIM illumination help with CL adjustment?
- the optic zone diameter of an RGP is based on pupil diameter
- too small OZ= flare/glare @ dim light like driving at night
what would an interpalp fit usually indicate in terms of lids?
- tight lid (holds the lend in place on the eye)= greater adhesion
- a larger or high upper lid that does not go past limbum= hard to get “lid attach” fit.
what would a lower lid fit usually indicate in terms of the possibility in pt. eyes? what about in lids?
- possible keratoconus, post surgical
- lids are loose so lens falls–least comfortable
- *type of lens likely BF, high torics
what is eccentricity? how does it relate to Cl? what is AVERGE corneal eccentricity?
- rate of change or flattening in curvature from apex to the periphery (limbus)
- steep cornea= high exccentricity
- average is e=0.50
how does the normal cornea move with aspherical shape?
-center is steepest and flattends out in periphery-slowly @ apex and fast @ limbus
what is shape factor and what’s the equation?
shape factor is how much eccentricity is happening in lens–> 1- (e squared)
-closer to 0= flatter cornea || closer to 1.0= like a parabola&high curves
what is indicative of a high eccentricity or high shape factor
- lots of corneal curvature
- possble kerotoconus
can you have same K’s and difference eccentricity? why/whynot
- yes!
- k’s only measure central 3mm, there can still be a lot of peripheral astig
what is toricity?
- meridional changes in curve
- the radius can have different radii of curvature in different meridians
what does the corneal apex measure usually
- steepest part of the cornea and where CL usually center
- can be @ middle usually, but may not and can change with kerotoconus
