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CL > fall MT > Flashcards

fall MT Flashcards

1
Q

what are the cornea layers–epithelium?

A
  1. superficial cells–microvilli/desmosomes, gap junction
  2. wing cells–desmosomes + gap junctions
  3. basal cells– desmosomes, hemidesmosomes + gap junction, junctional complexes
  4. BM= type 4 collagen + laminin
  5. ** optically smooth, protective against microbial invasion and chemicals, adherent surface for tear film, barrier against influx of water—peripheral langerhand cells
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2
Q

what’s in Bowman’s layer?

A
  • type 1, 3, collage fibers + proteoglycans
  • collagen fibers continuous with stroma
  • does not regenerate after injury
  • maintains epi struction
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3
Q

what’s in the Stroma?

A
  • 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
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4
Q

what’s in descemet’s membrane?

A
  • condensation of Type 4 collage + maninin
  • adhere to stroma
  • *BM of endo
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5
Q

what’s in the endothelium? what’s average # cells in young adult?

A
  • 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
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6
Q

what is the average corneal thickness centrally and peripherally?

A

overall= 500-550microns @ center, 660 @ periphery ( thicker @ periphery)

  • epi= 50 microns
  • stroma=thickest @ 450microns
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7
Q

what is the average corneal diameters (aka horizontal visible iris diameter (HVID)?

A
  • horizontal 10-13mm–> average is 11.7mm
  • vertical 9-11mm (veritcal is slightly smaller)
  • determines the over all diam. of the CL needed
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8
Q

what’s in the Palp conjunctiva vs. the Bulbar conj? what is generally found on the conj?

A

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
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9
Q

on the eye lid, what are the various parts and how do they adhere to the eye?

A
  1. out skin= loosely adherent to underlying muscle
  2. inner lid= TIGHTLY adherent to tarsal plate & palp lined
  3. tarsal plate= 0.75mm thick || densely packed collagen fibers
  4. meibomian glands= inside tarsal plates
  5. Glands= Zeiss + Moll @ the lash line
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10
Q

how do you measure the palp aperture height (PAH)? how is this used in CL assessment? Max/min values?

A
  • 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
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11
Q

how does lid POSITION affect CL assessment in fit?

A
  • 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)
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12
Q

what is likely to happen in a TIGHT lid vs. a LOOSE lid in lid tension for RGP fit?

A
  • tight lids= pull a lens upwards or squeeze it downward (watermellow seeds effect)
  • loose lids= move the lends downward (drops easily)
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13
Q

what is a normal blink rate? and how does it affect CL fit?

A
  • avg. blink rate= 10-15 blinks/min

- determines lens material to be used

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14
Q

what produces lipids in tears? aqueous? mucin? what is total tear film thickness?

A
  • *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
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15
Q

how does pupil diameter in DIM illumination help with CL adjustment?

A
  • the optic zone diameter of an RGP is based on pupil diameter
  • too small OZ= flare/glare @ dim light like driving at night
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16
Q

what would an interpalp fit usually indicate in terms of lids?

A
  • 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.
17
Q

what would a lower lid fit usually indicate in terms of the possibility in pt. eyes? what about in lids?

A
  • possible keratoconus, post surgical
  • lids are loose so lens falls–least comfortable
  • *type of lens likely BF, high torics
18
Q

what is eccentricity? how does it relate to Cl? what is AVERGE corneal eccentricity?

A
  • rate of change or flattening in curvature from apex to the periphery (limbus)
  • steep cornea= high exccentricity
  • average is e=0.50
19
Q

how does the normal cornea move with aspherical shape?

A

-center is steepest and flattends out in periphery-slowly @ apex and fast @ limbus

20
Q

what is shape factor and what’s the equation?

A

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

21
Q

what is indicative of a high eccentricity or high shape factor

A
  • lots of corneal curvature

- possble kerotoconus

22
Q

can you have same K’s and difference eccentricity? why/whynot

A
  • yes!

- k’s only measure central 3mm, there can still be a lot of peripheral astig

23
Q

what is toricity?

A
  • meridional changes in curve

- the radius can have different radii of curvature in different meridians

24
Q

what does the corneal apex measure usually

A
  • steepest part of the cornea and where CL usually center

- can be @ middle usually, but may not and can change with kerotoconus

25
Q

does the cornea have asphericity?

A
  • yes
  • radius of curvature is changing and ranges from 40-48D with avg @ 43.00D K’s
  • center curve may NOT be on the visual axis
26
Q

what’s the difference between regular astig and irregular astig?

A
  • regular astig can be corrected via Rx vs. irregular cannot–like keratoconus
  • irregular corneas= 2 principal meridians are NOT at right angles from each other

**due to degeneration, disease, injury

27
Q

how does the transition zone (LIMBUS) change?

A
  • cornea to limbus= more steep & curved
  • curve will flatten @ sclera
  • *topography can change a lot in the limbal area
28
Q

how does the transition zone (LUMBUS) change?

A
  • cornea to limbus= more steep & curved
  • curve will flatten @ sclera
  • *topography can change a lot in the limbal area
29
Q

how does the sclera look vs. cornea?

A

sclera is sig. flatter than cornea–affects sclera lenses

**avg. radius of curve= 11mm

30
Q

how is a placido disk used?

A
  • craetes “ring” cut outs of the reflected corneal pict
    con: if you have really steep cornea, these rings can double up and you get a “dead zone” which are inacurrate readings of the curve due to getting an “Avg” of the rings rather than what each ring depth is
31
Q

how is a placido disk used?

A
  • craetes “ring” cut outs of the reflected corneal pict
    con: if you have really steep cornea, these rings can double up and you get a “dead zone” which are inacurrate readings of the curve due to getting an “Avg” of the rings rather than what each ring depth is
32
Q

what is difference between axial and tangential maps?

A
  • axial =1 central reference sphere

- tangential= curves from relative to normal at each point (each part has its own reference sphere)

33
Q

what is difference between axial and tangential maps?

A
  • axial =1 central reference sphere

- tangential= curves from relative to normal at each point (each part has its own reference sphere)

34
Q

what is the difference between using a (-) carrier lenticular vs. a (+) carrier lenticular?

A

(-) decreases CT @ low myopes and increases lid attachment

(+) lenticulars decreases edge thickness in high myopes (over -.600)–makes lens more ‘curved’ on the edges

35
Q

if a patienthas internal astigmatism, how does a LL affect that?

A
  • internal astig= lenticular astig

- you will get RISIDUAL astig

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