CL (Soft CL) Flashcards
Parameters (BBL-CLW) (WRF-TIM)
- Base curve
- Back vertex power
- Lens diameter, optic zone diameter
- Center thickness, edge thickness
- Lenticulation / Edge design
- Water content
- FDA groupings
- Wear schedule approval
- Replacement modality
- Tints
- Inversion markers
- Manufacturing technique
also referred to as Sagittal depth (sag) or Vault
Base Curve
tend to be much flatter than K due to large diameter
Base curve
Base curve typical range
8.00 to 9.20mm
determined by BC, front curve, CT, n
Power
assume that LL is plano for most SCLs
Power
Power: effective power not altered by lacrimal lens (True or False)
True
larger than RGPs in general
Lens diameter/ optic zone
increases stability & comfort
Lens diameter/optic zone
Lens diameter/optic zone typical mm
13.5 to 15mm
creates greater sag, resulting in need for flatter BC’s
Lens diameter/optic zone
decreases tear exchange
Lens diameter/optic zone
thinner than RGPs due to decreased fragility of material (greater flexibility)
Center & Edge Thickness
affects Dk/L
Center Edge & Thickness
Center & Edge Thickness: edge profile may be more important to consider (True/False)
True
Min CT = ______, increases for higher water content materials
0.03mm
- due to large diameter, all SCLs are lenticulated to maintain thin profile
- edge designs vary
Lenticulation/Edge design
water is bound within a hydrophilic polymer matrix to provide flexibility & oxygen permeability
Water content
The amount of _____ determines material characteristics
Water
Water content range
Range: 25% to 74%
Low: <50%
High: >50% (FDA)
Water content (Low) (GLUCEF)
- Good durability & handling
- Fewer deposits
- Lower Dk
- Can be made thinner
- Used more often than daily wear
- Exception: SiHy
Range: Low: <50%
Water content (High) (HUMMP)
- Higher Dk
- Used more often than extended wear
- More deposits
- Poorer durability & handling
- Must be made thicker
Water content: For ___________, less water content means higher silicone content, and therefore higher Dk
Silicone hydrogels
Water content
PureVision:
Focus N&D:
PureVision: 36% water Dk: 110
Focus N&D: 24% water, Dk: 140
Silicone hydrogels: hydrophobic
Silicone
Silicone hydrogels: hydophilic
Hydrogel
What is other name for silicone
Polydimethylsiloxane
Silicone Hydrogels AerGel Technology (WOSH)
-Oxygen
-Water
-Hydrogel matrix
-Silicone matrix
FDA Groupings
Group 1: low water, non-ionic
Group 2: high water, non-ionic
Group 3: low water, ionic
Group 4: high water, ionic
In FDA groupings, what groups are non-ionic
Group 1 & 2
In FDA Groupings, what groups are ionic
Group 3 & 4
In FDA Groupings, what groups are low water
Group 1 & 3
In FDA Groupings, what groups are high water
Group 2 & 4
Water Schedules: wear during waking hours only, no overnight wear
Daily wear
Water Schedules: wear overnight up to 7 days in a row, any lens approved for EW
Extended Wear
Wear Schedules: wear continuously up to 30 days in a row, only for silicone hydrogels
Continuous wear
Replacement Modality (CFD)
- Conventional
- Frequent replacement
- Disposable
lens is replaced when it needs replacing
Conventional
if a lens is lost/damaged, a replacement must be purchased
Conventional
Conventional SCL typically lasts
12 months for a SCL
patient receives one pair of lenses at a time
Conventional
more lens care required, more deposit related complications
Conventional
also called Programmed Replacement
Frequent Replacement
Frequent Replacement: lens is replaced on a regular schedule ___weeks to ____months
2 weeks to 3 months
Lens is reused after removal & disinfection
Frequent Replacement
confusion with various replacement schedules
Frequent Replacement
fewer complications, still requires lens care, more costly
Frequent Replacement
one time use, no lens care, most costly, greatest convience
Disposable
(Disposable) Daily wear:
Extended wear:
Continuous wear:
DW: 1 day
EW: 1 week
CW: 1 month
Tints
- Handling/ Visibility
- Enhancing
- Opaque cosmetic
- Prosthetic masking
can see more easily in case, sink, or counter
Handling/Visibility Tints
light tints to aid in lens handling
Handling/Visibility Tints
not meant to change eye color
Handling/Visibility Tints
can change eye color in light blue irises
Handling/Visibility Tints
virtually all current lenses have __________
handling tints
change eye colors of light irised patients
Color Enhancing Tints
combines with natural eye color to create a new color
Color Enhancing Tints
Color Enhancing Tints: change eye colors of light irised px
- Blue, green, hazel eyes
- Will only darken brown eyes
tints that change dark irises to other colors: “Brown eyes to blue”
Opaque Tints
may see some iris through clear pupil
Opaque Tints
mask underlying iris color, px may notice some blur around the edges
Opaque Tints
mask underlying disfiguration of the eye (Corneal scars & Iris defects)
Prosthetic Tints
Prosthetic Tints: what underlying disfiguration of the eye (CI)
- Corneal scars
- Iris defects
can be clear or occluder pupil lens
Prosthetic Tints
very expensive & long production time, can be painted any color
Prosthetic Tints
Ciba: Special Eyes Program
CooperVision: Prosthetic lenses
Adventure in colors
Crystal Reflections
Prosthetic Tints
- tell a px if a lens is inside-out
- tells you if lens is inside-out on the eye
Inversion Markers
many manufacturers now put letters/numbers on their lenses
Inversion Markers
Lens position & corneal coverage: Vertical & lateral assessments
- Superior-Central-Inferior
- Temporal-Central-Nasal
full corneal coverage is necessary at all times
Lens position & corneal coverage
Lens position & corneal coverage: Assessment is made in primary gaze
- Eyelids in normal position
- Head in normal position
Lens positioning & corneal coverage: Factors affecting lens position (SEL)
- Sagittal depth
- Lens diameter
- Eyelid interaction
an assessment of lens movement induced by the normal blink, assessed in primary gaze
Blink Movement in Primary Gaze
Blink Movement in Primary Gaze acceptable blink movement range ___ to ____mm. At no time should the inferior cornea be exposed during this movement
0.5 to 2.0mm of vertical excursion
the amount of lag movement on upgaze is assessed
Upgaze movement
Acceptable amount of upgaze lag movement range
0.5 to 2..0mm
amount of lens movement on blink while px is looking up should also be made, usually greater than blink movement in primary gaze. How many mm is the acceptable movement up, as long as inferior cornea is not exposed
2.0mm
an assessment of lag movement induced by lateral eye excursions
Lateral lag movement
Lateral lens movement on lateral eye excursions range
0.5 to 2.0mm
Lateral lag movement:
- a _____ fitting lens will not have lateral lag movement
- a ______ fitting lens will lag excessively, exposing some of the cornea
tightly, loosely
this is a supplemental observation
Lateral lag movement
the lower lid can be used to manually push upward on the lens to determine if the lens is freely floating on the cornea
Push-up movement
this test is supplemental
Push-up movement
Factors affecting lens movement (BELLLL)
- Base Curve
- Lens diameter
- Eyelid interaction
- Lens thickness
- Lens modulus
- Lens hydration/dehydration
Dehydration effect on soft lens parameters:
-steeper base curve
-smaller diameter
-slight decrease in lens power
Dehydration effects on soft lens parameters
- steeper base curve
- smaller diameter
- slight decrease in lens power
Over keratometry mires
Auxiliary Observations
(Auxiliary observations) Over-keratometry mires
steep fit:
flat fit:
Steep fit: blur-clear-blur
Flat fit: clear-blur-clear
Blurring of mires can also be due to lens surface drying
Auxiliary observations: Retinoscopy reflex
Steep fit: central distortion
Flat fit: inferior distortion
Auxiliary observations: conjuctival drag: movement of vessels with tight or adhered lens
DDX: Loose conjunctiva
Auxiliary observations: what are the indications for tight fitting lenses (BLV)
- Bubbles at limbus indicate tight fitting lenses
- Vessel blanching & engorgement with tight lenses
- Lens imprint after removal with tight lenses
What are the auxiliary observations
- Over-keratometry mires
- Retinoscopy reflex
- Conjunctival drag
& more
What are the soft lens optics (PLAVE)
- Vertexing
- Lacrimal lens
- Predicting the OR
- Effect of lens on Optics
- Aspheric designs
What are the different tints (POCH)
- Handling/Visibility Tints
- Color Enhancing Tints
- Opaque Tints
- Prosthetic Tints
What are the Soft lens fit characteristics (BULLPA)
- Lens position & corneal coverage
- Blink movement in Primary Gaze
- Upgaze movement
- Lateral lag movement
- Push-up movement
- Auxiliary observations
Vertexing: be sure to vertex any meridian _____ or over
+4.00
the CLP is equal to the vertexed refraction or its ____ equivalent
SPH
assume that for most soft spherical lenses, the LL = _____, regardless of BC or K-reading
plano
LL: if SR = -3.00, the above lens is ______
optimal
Predicting the OR: since there is no LL, the OR is simply the difference between refraction & CLP. Formula for OR
POR = SRv - CLP - LL
Effect of lens on Optics: in steep lens
Steep lens: poor draping, poor VA between blinks
Effect of lens fit on Optics: poor draping, poor VA between blinks
Steep lens
Effect on Lens Fit on Optics: in flat lens
poor draping & excessive movement, poor VA right after the blink
Effect of Lens Fit on Optics: poor draping & excessive movement, poor VA right after the blink
Flat lens
Effect of Lens Fit on Optics: poor hydration & optical quality, poor VA between blinks as lens dries
Dry lens
Effect of Lens Fit on Optics: in dry lens
poor hydration & optical quality, poor Va* between blinks as lens dries*
Aspheric designs: _______ reduce spherical aberration & may increase depth of focus
Aspheric front surfaces
improves optical quality, esp for higher powers
Aspheric designs
may improve vision for low astigmats & early presbyopes
Aspheric designs
What are Aspheric Designs brands
- Ciba Choice AB
- Coopervision Frequency Aspheric
Aspheric design: light rays converge at meeting area rather than a single focal point
Traditional spherical design
Aspheric design: focuses light better to a common focal point
Frequency 55 Aspheric
What is the FDA Group 2 classification for SCL?
High water, non-ionic
Which replacement modality requires least lens care
Disposable
Which type of tint is used to help patients with corneal scars or iris defects
Prosthetic tint
What is the typical diameter of SCL
13.50 to 15.00mm
The term “vertexing” is applied when prescription is
More than +4.00D
Which water content category typically has fewer deposits
Low water content lenses
What range of blink movement is considered acceptable for SCL
0.5 to 2.0mm
Which is true about lenses with higher content
They are more prone to deposits
Which tint is NOT designed to change eye color
Handling/Visibility tint
Which lens fit would result in poor vision between blinks due to poor draping
Steep lens fit
Which parameter primarily affects the oxygen permeability of SCL
Water content
tightly fitting SCL may result in
Conjunctival drag
Which is characteristic of silicone hydrogel lenses
Better oxygen permeability with less water content
What is the main consequence of a poorly hydrated lens
Poor vision between blinks
Which tint is primarily used to darken the eye color of light eyed individuals
Enhancing tint
