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77 Cards in this Set
- Front
- Back
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What percent of all cl wearers wear GP's
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10%
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what type of lenses offer better visual acuity - soft cl or GP?
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GPs
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the incidence of keratitis is much lower with use of soft cls or GPs?
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GPs
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what curve of the gp is known as the fitting curve
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base curve
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what curve of the gp contains the refractive error correction?
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base curve
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the size of the optic zone is dependent on what two variables?
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base curve & pupil size (needs to cover pupil)
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a steeper base curve needs a smaller or larger optic zone?
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smaller
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what is the name of the curve immediately outside the base curve?
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secondary curve
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are intermediate curves found in all gps?
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no, only those with more than 3 curves
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the peripheral curve is sometimes referred to as the _____ curve
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tertiary
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what curve of the gp is responsible for the alignment of lens to cornea?
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base curve
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what curve of the gp is responsible for the transition from the central cornea to the flatter corneal periphery?
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secondary curve
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what curve of the gp is responsible for controlling the edge lift?
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peripheral curve
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what curve of the gp is responsible for allowing tear exchange?
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peripheral curve
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if you order a "standard" tricurve lends, what radius of each curve will be sent?
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secondary curve = BC + 1.5mm
peripheral curve = BC + 3.0mm |
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what is the standard PC radius that is made when a "flat tricurve" is ordered?
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3.5 mm flatter than the BC (BC + 3.5mm)
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when describing edge lift, which term is more commonly used - axial edge or radial edge?
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axial edge lift - which is the Z value
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Z, axial edge lift, is a measurement of what?
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vertical distance from the lens edge to the extension of the base curve
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E, radial edge lift, is a measurement of what?
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the extension of the lens egde perpendicular to the extension of the base curve
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what type of fitting method are you using when you fit according to the Rx and K readings?
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empirical fitting
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what type of cl is best for:
-7.50 -1.00x180 |
soft sph
soft toric soft aspheric GP sph |
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what type of cl is best for:
+6.50 -4.00x090 |
GP bitoric (bc cyl >-2D)
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what type of cl is best for:
+1.00 -4.50x180 |
GP bitoric
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what type of cl is best for:
-1.50 -0.25x090 |
soft sph
GP sph |
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under what conditions are soft torics indicated?
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> -.75D
-0.75D diff btw corneal & refractive astig -Rule of 4s - if cyl is > 25% of the sph, use soft torics -significant amount of CRA |
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under what conditions are GP torics indicated?
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-when cyl >> sph power
-low sph (near plano) -corneal toricity > refractive astig |
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if base curve is steepened, what happens to the sag depth?
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increases
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if the base curve is flattened, what happens to the sag depth?
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decreases
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what happens to the sag depth when OAD is decreased?
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decreases
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for every 0.5mm decrease in OAD, what must we do to the base curve in order to maintain the same fitting relationship?
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steepen it by 0.25D
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if OAD is increased, what happens to the sag depth?
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increases
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for every 0.5mm increase in OAD, what must we do to the base curve in order to maintain the same fitting relationship?
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decrease (flatten) it by 0.25D
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if OZD is increased, what happens to the sag depth?
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increases
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what affect does a change in the peripheral curve have on the sag depth?
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none
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if OZD is decreased, will the lens fit flatter or steeper?
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flatter - so bc must be steepened in order to maintain the same fitting relationship
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what are the four steps in designing a GP lens?
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1.choose appropriate diameter
2.select proper base curve 3. evaluate lens fit 4. select proper power |
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what four things are considered when choosing an appropriate lens diameter?
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1. lid position & palpebral aperature size
2. corneal curvature (steeper corneas need a small diameter) 3. power of lens (thick lenses need small diameter to keep it light) 4. type of lens |
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what size diameter is considered large?
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9.4mm and greater
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what size diameter is considered small?
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9.0mm and less
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what type of fitting style is used when the lids cover the superior limbus?
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superior-central or lid-attached fitting styles
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What diameter is best when fitting a pt whose lids cover the superior limbus?
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large diameter (greater than 9.4)
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what affect does the pupil size have on the optic zone diameter of a lid attached lens?
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none
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what affect does the pupil size have on the optic zone diameter of an interpalpebral fitting lens?
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it determines the optic zone size (pupil <5mm = 7.5 bc, pupil >7 = 8 bc)
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what size optic zones are used with lid attached fitting lenses?
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7.8 - 8.5 (larger than avg)
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how is the bc determined in a lid attached fitting lens?
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flat K or slightly flatter
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how is the bc determined in an interpalpebral fitting lens?
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steeper than flat K, based on corneal cyl
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how much does the OAD have to be changed in order to have a significant effect?
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0.3mm
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steeper base curves - tend to decenter...
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inferiorly
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flatter base curves tend to decenter
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superiorly
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extremely flat base curves tend to decenter...
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inferiorly (fall)
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what two methods can be used to evaluate lens fit?
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slit lamp
burton lamp |
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what are the big disadvantages of the burton lamp?
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(hand held UV lamp held in front of pt)
- magnification can't be varied - cornea can't be inspected |
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the ideal gp lens mvmt
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1.0 - 2.0mm
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what is the importance of good gp lens mvmt?
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-allow for good tear exchange
-flush out metabolic waste -maintain normal corneal metabolism |
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how thick does the tear film have to be in order to fluoresce?
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20 microns
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ideal edge width
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.4mm
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how do we correct an insufficient edge lift?
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flatten PC
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if egde lift is too great, the lens may decenter....
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superiorly
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how do we correct an excessive edge lift?
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steepen bc
steepen pc decrease z value |
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troubleshooting an inferiorly displaced lid attached lens...
OAD, BC, PC, CT |
inc OAD
flatten BC & PC dec CT consider lenticular |
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troubleshooting an inferiorly displaced interpalpebral lens...OAD, BC, PC, CT
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dec OAD
steepen BC & PC dec CT consider lenticular |
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troubleshoot a superiorly decentered lens
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usually only a prob if pupils are large
- steepen BC - increase CT consider thin, sspheric |
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troubleshoot a lateraly decentered lens
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increase OAD
steeper BC consider aspheric back surface (more common on ATR corneas) |
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troubleshoot a lens with flexure..
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inc CT
use lower DK material fit lens flatter |
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initial poor vision in a gp lens could be due to...
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lens not wetting
flexure |
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poor vision that has acquired after a time of wearing GPs could be due to...
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lens warpage
scratched lens lens deposits power change due to aggressive cleaning |
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how much must we change the OAD/OZD to be clinically significant?
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0.3mm
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how much must we change the BC to be clinically significant?
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0.50 D (.1mm)
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how much must we change the CT to be clinically significant?
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0.03mm
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how much must we change the PC radius to be clinically significant? What about the PC width?
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radius - 1mm
width - .2mm |
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the desired edge or center thickness of CL is that of a ____D lens
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-3.00D
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powers greater than _____D should have a plus lenticular design
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-5.00
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what powered lenses should have a minus lenticular design?
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-1 and less
all plus lenses |
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T/F giving a pt colored lenses to differentiate btw OD and OS will change the pts eye color
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FALSE
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what colors can be used for OD lenses to differentiate them from OS?
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Green
Gray (Red in Ortho K only) |
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what colors can be used for OS lenses to differentiate them from OD?
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Blue
(yellow in Ortho K only) |
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what colors are used for the OD and OS ortho K lenses?
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red OD
yellow OS |
