Exam 1 Flashcards
Absolute CL contraindications
- lack of motivation and/or compliance
- diseased eyes (if being fit for purely vision reasons and patient has a diseased eye, the pt is better off with glasses)
Relative CL contraindications
- Lid margin disease (MGD, bleph) that affect the tear film
- Recurrent corneal erosions
- uncontrolled diabetes (decreased wound healing)
- Dirty, dusty enviornment
- active sinus/allergy problems
- poor blinking
- pathological dry eyes
- past ocular infections
- sensitive eyes
Tests in exam for fitting CL
- all normal routine tests plus
- corneal curvature and/or topography
What is the most important part of the history for a CL fit?
-motivation to wear CL
Questions to ask during CL fitting history
- how often will you wear them
- what activities will you do while wearing them
- occupation and hobbies
How does a lot of computer work impact CL
- decreased blink rate which will dry out the front surface of the CL, decreasing the clarity and making the back surface tighter
- makes CL more uncomfortable
Reasons for CL wear
- occluder for VT (ie amblyopia)
- improve color discrimination when color deficient
- occupational concerns
- sports/recreation
- inconvenience of GL
- cosmesis
Contact Lens History
- What type of lenses do they/have they worn?
- Any issues with the CL
- Do you want to change lens types, replacement schedule?
- How long will they wear them
- How often do they replace the lenses
- How old is their current pair
- What care regimen do they use?
- Have they ever had any complications?
Systemic conditions that can cause ocular dryness with CL?
- allergies
- sinusitis
- mucous membrane dryness: eye, nose, mouth
- nocturnal lagophthalmos
- diabetes: retarded wound healing leading to keratitis
- convulsions, epilepsy, fainting
- collagen vascular disorders: Sjogren’s, rheumatoid arthritis
- Prgenancy: 1st and 3rd trimesters
- hyperthyroid: exophthalmos
Systemic medications that can cause ocular dryness
- hormones
- birth control
- antihistamines
- anti-anxiety
Ocular medications and CL
-pt should wait 15 minutes after instilling drops to put in CL
VA and CL fitting
-take aided and unaided before placing CL on eye
How much should you blur a patient during binocular balance?
+2.00 over habitual Rx
Vertex conversion
Fc = Fs/(1-dFs)
Fc is power at cornea
Fs is power of lens
d is the change in distance in m (in the case of CL it is equal to the vertex distance)
ALWAYS do this for an Rx +/-4.00 D or greater in ANY meridian
Vertex conversion trends
- Myopes will take less minus in CL
- hyperopes more plus in CL
Near Add power formula
Add power = (age-35) x 0.1
Keratometry
- measures central 3 mm of cornea
- can be used to evaluate tear film (non invasive TBUT)
- matters for soft and GP lenses, but more so for GP
TBUT for CL exam
- use non-invasive
- NaFl can be absorbed by the contact lens
- when mires blur and break means tear film quality is deminished (longer than TBUT, normal is»_space;15 seconds or first blink)
Flat, steep cornea
- Flat: 40 D, larger mm
- Steep: 48 D, smaller mm
Diopter to radius formula
D = (n'-n)/r r = (n'-n)/D
How to measure corneal curvature
- autok
- keratometer
If mires are missing/distorted:
-corneal topography
When is corneal topography necessary?
- irregular astigmatism
- keratoconus
- post-surgery
- orthokeratology
- corneal trauma
costs more for pt, which is why we usually rely on keratometry
Corneal Topography pros
- measures central and peripheral cornea
- checks for irregularities
- checks for apex displacement
- high cylinder
- irregular keratometry mires
- corneal thickness (Orbscan)
Corneal topograher types
- Placido’s Disc (Reynold’s)
- Orbscan/Pentacam
- Humphrey/Atlas/Reseevit
Placido disc (Reynold’s)
- corneal topographer
- often used with kids
- don’t charge extra
- checks for irregularities or distortion of the reflection of rings on the cornea
Orbscan/Pentacam
- corneal topographer
- gives corneal thickness and other variables in addition to curvature
Humphrey/Atlas/Reseevit
- gives standard mapping
- Atlas is most common in determining CL fit
Slit lamp for CL
-illumination:
medium to low intensity (not high because we need to control tear layer)
direct; 15-45 degree angle
-Mag: 10-16x for global view
never have beam directly into pupil - stimulates macula and reflex tearing
How to check for endothelium changes in the cornea
- sclerotic scatter
- specular reflection
- only necessary if you see a hazy cornea
Tear prism
- flat/convex is good
- concave, narrow or missing means the patient does not produce many tears
Corneal Staining Grades: corneal divisions
-1 is central
-2 is temporal
-3 is nasal
-4 is superior
5- is inferior
Corneal Staining Graes: types
- micropunctate
- macropunctate
- coalescent macropunctate
- Patch
Corneal Staining Grades: extent
- 1-15%
- 16-30%
- 31-45%
- > 45%
Corneal Staining Grades: Depth
- superficial epithelium
- deep epithelium, delayed stromal glow
- immediate localized stromal glow
- immediate diffuse stromal glow
Schirmer Test
- place temporally to avoid scratching cornea
- >10 is normal
Phenol Red Test
-10 to 24 is normal
place temporally
measure with PD ruler
Lid Wiper Epitheliopathy
LWE
- upper lid junction between the cutaneous and conj tissue
- grade the NaFl staining of the junction area
- a lot of irregularity means dry eye problem
Tear Lab
- measures tear osmolarity
- >300 indicates dry eye
CL Slit Lamp: Lids and Lashes
- look for bleph and demodex: if you see bleph twist the lashes to see an animal crawl out. Must treat both before putting a CL on the eye
- evert upper and lower lids to view the palpebral conj:
- look for papillae, follicules, scars and concretions
Zones of lids
- junctional zone (close to fornix)
- middle
- closest to lid margin
- Nasal
- temporal
*zones 1 through 3 are the most important when fitting CL
GPC
giant papillary conjunctivitis
initial zone to get papillae with soft/Si-Hy lenses
-zone 1
as it worsens it will expand into 2 and 3
initial zone to get papillae with GP CL
-Zone 3
as it worsens it will expand into 1 and 2
Mastrota Meibomian paddle
-flat surface used to express meibomian glands
expressing Meibomian glands
- normal tear layer: secretions are clear
- MGD: glands clogged or turbid secretion
CL Slit lamp exam: conj
- limbal injection
- pannus
- edema
- drag
- pinguecula
- pterygium
**most important of these is to look for conj drag
Conjunctival Drag
-young pts will have less drag than older because as we age the connections between the sclera and the conj weakens
HVID
horizontal visible iris diameter
- essentially the size of the cornea
- use PD ruler to measure
-small cornea 13 mm: CL will not stay on the cornea well
Pupil size in CL exam
- taken in normal illumination
- large pupils: cause more halos
- small pupils in presbyopes: does not allow for full use of MF CL
-Small: 7 mm
What type of lid tension is more difficult to adapt to GP lenses?
-tighter
VFW
Vertical fissure width
- usually 8 to 12 mm
- hard to take with PD ruler because patient may blink with ruler close to face
CL Anatomical Mesaurements Required
- HVID
- Pupil diameters in bright and dim
- palpebral aperture height
- lid position
- lid tension
Iris color and corneal sensitivity
-less pigment (lighter) means greater corneal sensitivity
Typical blink rate
- 10-15 blinks per minute
- 2-3 blinks per 15 seconds
best to measure when talking to patient. If you tell them what you are doing it will alter their blink rate
How are GL and CL different?
- power: vertex convert CL; tear film affects GP power
- Accommodative demand and convergence: no prismatic effect with CL
Myope prism induced with GL during reading
- Base in which causes:
- less convergences so less accom
- CL have no prism, so myopes will likely converge and accommodate more with CL
- hyperopes will be the opposite (reason pre-presbyopes like CL more than glasses)
Magnification: CL vs GL
CL:
- Myopes: less minification (larger image with CL)
- hyperopes: less magnification (smaller image with CL)
***CL give more realistic image size
Field of view: CL vs GL
CL has a larger field of view due to:
- no frames
- less aberrations
- no induced prism
- less image curvature
- less oblique astigmatism
When is a screening done?
When you know
- modality: daily/extended wear
- replacement schedule
- type of lenses
Soft CL materials
- Hydrogels (SCLs): made of a polymer and water
- Silicone Hydrogels (Si-Hy): polymer, water, silicone to increase O2 permeability
When can you choose a spherical soft lens?
if the refractive cylinder power is
When can you choose toric lenses?
the refractive cylinder is:
- > -0.75 D AND/OR
- > 25% of the sphere power
Steps for cyl power
in 0.50 D increments
When can you choose GP sphere lenses
Refractive cyl=corneal cyl,
Why do GP CL work for keratoconus
-the pt’s tear layer will fill in the irregulatrites
When can you choose GP toric lenses
-corneal cyl >2.50 D
Options for schedule of CL
- Daily (only while awake)
- flexible (can wear occasionally while sleeping)
- extended wear (lenses worn 3 to 7 days and nights)
- continuous wear (wear up to 30 days and nights)
CL replacement options
- daily
- 1 week
- 2 weeks
- 1 month
- quarterly
- semi-annually
- annual
PMMA
- polymethyl methacrulate
- rarely used
- very durable
- very poor O2 transmission so not healthy for eyes
- may distort or cause an irregular cornea
IEI CL costs
Fit: $90 up to $750
-boxes: $25-55/box up to $220
CLAMO
I prefer to use CLAMUPR
- C: corneal coverage
- L: Lens Centration
- A: Acuity
- M: Movement
- O: Other
- U: Upward movement
- P: Pushup test
- R: Rapid blink test
Start with C. If any of these are wrong, then stop and get a new lens
CL parameters
- base curve: posterior curve on CL
- Diameter (size; overall diameter)
- lens power
- lens thickness (center thickness)
*we can only modify the first 3
Base Curve
one size usually fits all -typically fit 4 to 5 D flatter than the flattest K of the pt -Use: Steepest BC if flattest K>45D Middle BC if flattest K = 41 to 45D Flattest BC if flattest K
Which to choose if the lens comes in 2 BC
- Use steeper BC if the flattest K>45 D
- Use flatter BC if the flattest K is less than or equal to 44
Which BC for hydrogel?
flatter is best due to tightening effect as the lens dehydrates
Which BC for SiHy
steeper due to
- less evaporation of the lenses
- lens is stiffer so if it is too flat it will be more uncomfortable
equation for determining BC for pt
Avg/Flatter K (mm) + 0.8 = soft lens BC
use n’-n/K * 1000 to get the Avg K in mm
Formula for selecting lens diameter
OAD = HVID + 2
needs to extend 1 mm beyond the limbus
Lens diameter requirements
-need the CL to extend beyond the limbus to avoid limbal irritation
OAD used most often
13.8, 14.0, 14.2
when do you use Spherical equivalent for a CL
-cyl power
Residual astigmatism
equals the refractive cylinder
typical vertex distance used
12 mm
You have a pt with -1.00-0.50x180. What CL do you give? What will they overrefract at?
CL Rx: -1.25 DS
overrefract: +0.25-0.50 x180
Effects of soft CL drying on power
-as it dries the lens becomes a little more minus
Residual cyl of soft CL
-occurs when using spherical equivalent
-basically, it is just the cyl power left over in the written Rx.
I.e. -4.00-1.00x180
CL power: -4.50
residual cyl -1.00x180
Overrefraction
-if using a spherical CL, only do a spherical refraction because you know what your residual cyl will be
Time for soft lenses to reach equilibrium
-
equilibriation
-the process of a pt’s tears replacing the fluid in a CL
Steps:
1. stable
2. 50/50 mix of tears and saline in lens = tightest point
3. lens loosens and is stable
When is a CL at it’s tightest point?
- when the CL is 50% saline 50% pt tears (at about 10 minutes)
- due to a differential in osmolarity of the lens itself
Scleral wash
- decenter lens onto temporal sclera
- blink
- look temporal to allow to recenter
this will remedy a lot of discomfort problems because more tears accumulate on sclera than cornea
Where do you check for movement
-inferior nasal quadrant
What governs lens fit
- relationship between sagittal heights of lens and anterior eye (lens>eye)
- anterior eye topography including cornea
- blink induced negative pressure under the lens
- physical properties of the lens
- lid characteristics
- lid/lens interactions
Sagittal height
sag
Using the same diameter:
-shorter sag means flatter BC (looser lens)
-bigger sag means steeper BC (tighter lens)
if we kept the BC the same and wanted a larger diameter, the sag gets larger (so tighter lens)
if we wanted a smaller diameter the sag gets shorter (looser lens)
Corneal coverage
- loose fitting lens will have inferior corneal exposure and edge of CL may flare out
- tight fitting lens will have full corneal coverage
**cannot differentiate between good fit or tight fit with corneal coverage
Lens fit
- good fit: equal nasal and temporal
- loose fit: superior temporal decentration (needs larger OAD or steeper BC
- tight fit: equal or low (needs flatter BC or smaller OAD)
Acuity
-vision should be stable when blinking
-loose CL:
blurry immediately after blink then clears with eyes open (loose, blur, clear = LBC); the blink pushes the edges and bunches up the middle
-tight CL:
clear immediately after blink but blurry with eye open (tight, clear, blur=TCB); the blink pushes the CL against the eye
*this IS a good way to differentiate between good fit and tight fit
What controls CL movement
- thickness of the lens
- tautness of the lids
thin lenses don’t move much
-plus lenses have thin edges so the lens may not move as much because the lid can’t grab it
How much movement will a 0.035 mm thick CL have? 0.06 mm? 0.12 mm?
- 0.035 mm: perceptible movement
- 0.06 mm: should be about 0.25-0.50 mm movement
- 0.12 mm: 0.50-1.0 mm movement
Normal measurements of a CL and how to tell how much it moves
- HVID is 12 mm
- OAD is 14 mm
so, distance between CL edge and limbus is 1 mm if lens is well centered
-if the lens moves halfway to the limbus it is 0.50 mm movement
How much does a loose fitting lens move? Tight?
> 0.25-0.50 mm
-less movement, unless really tight then it moves more
Determining CL fit from pushup test
- good: easy movement
- loose: way too easy; edge of lens may lift up
- tight: difficult to move
Good fit lens summary
- well centered
- lens moves easily on push up test
- perceptible movement seen with blink
- easy to move with push up test
Tight fit lens summary
- centered on the cornea
- good coverage
- difficult to move with push up test
Loose fit lens summary
- push up test is way too easy; lens almost pushes off eye
- full blink makes CL move significantly more
- lens may or may not decenter
- if decentered it wil move superior temporally
- Loose, blurry then clear
- will be more uncomfortable for pt
Rapid blink fits
good: easy movement, more, cornea covered
loose: easy movement, cornea exposed
tight: little movement
Vessels and lens fits
- good: no blanch, may see drag
- loose: no blanch
- tight: may see temporally
- very tight: leads to adherence which makes it very hard to dislodge (use artificial tears to lubricate for removal)
Retinoscopy and lens fits
- Loose: edges are fuzzy, especially on top and bottom
- tight: fuzzy center
- dirty lens: spotty reflex
Over-keratomertry
over K = K + CL power
ex. K= 43.00, CL power = -2.50
over K = 43.00 + (-2.50) = 40.50
What is your goal for ordering CL
-order loosest, smallest lens that is stable with good VAs
What do you specify on CL order
- brand
- base curve
- size
- power
- color
- # of boxes
- replacement schedule
- name
- how to contact them
- type of care product
How to document CLAMO for good fit lens
- C: full coverage
- L: equal
- Acuity: stable
- M: perceptible to 0.50 mm
- O: easy pushup
Clamo tight fit
o Corneal coverage: full
o Lens centration: equal
o Acuity: fluctuating (CBS) – clear right after the blink, then blurry
o Movement: none, blanching
o Other: push-up difficult, rapid blink no movement
o ***Correct for a tight fit using a CL with flatter BC or smaller OAD
8.4 – 8.7 with same size
14.0 – 13.8 with same BC
CLAMO loose fit
o Corneal coverage: inferior exposure
o Lens centration: decenters high, temporal
o Acuity: fluctuating (LBC) – worsens immediately after blink
o Movement: > 0.75 mm or erratic
o Other: push up displaces, edge lift
o ***Correct for a loose fit using a CL with steeper BC or larger OAD
8.6 – 8.4 with same size
13.8 – 14.2 with same BC
Why do you not put fluorescein on a soft CL
-good environment for pseudomonas to grow, which affects the cornea
Soft CL disadvantages
- increased risk of infection (main)
- prone to deposits
- not as durable
- less quality of vision
- poor O2 transmission of hydrogel
- can’t modify/verify
- preservatives
- limitation of correction
Why are SiHy CL used the most
-high O2 permeability
Modulus of Elasticity (MPA)
a material's ability to keep it's shape when stressed High: -stiffer -easier to handle -feels thicker; less comfortable -can be cut thinner
Low: (high water content
- floppier
- less strong
Wetability
- keeps CL surface clear and comfy
- slows evaporation (can be done by surface treatments or wetting agents added into material)
Ionic charge and solution compatibility
-negative ionic charge: causes greater reaction to solutions than positive (ie negative makes solution preservatives stay on CL so pt may have more irritation
**ionics absorb more proteins
Low water content
High water content
> 50%
*58% is common
O2 transmission and water content
Soft lenses:
-greater transmission for high water content
SiHy lenses:
-greater transmission for low water content
Water content formula
weight of water/weight of hydrated gel x 100
CL inventor
Otto Wichterle (Czech)
FDA groupings of hydrogels
Group 1: low water, non-ionic Group 2: high water, non-ionic Group 3: low water, ionic Group 4: high water, ionic Group 5: SiHy
Which group of hydrogels can you not use heat to disinfect?
Group 4
FDA SiHy groupings
Group 5
-usually similar to hydrogel group 1 or 3 (ie low water)
Dk value
Units: Barrer
- higher means more O2 permeability
- increase logrithmically with water content increase for hydrogel, decreases for SiHy
First SiHy daily disposable lens?
-Acuvue TruEye
Dk/t
transmissibility
Fatt Dk/t units
-permeability divided by thickness
-a material always has the same permeability, but if the lens is thicker, less O2 is trasmitted
-this value more important for knowing how much O2 makes it to the eye
largest O2 supplier to the cornea?
limbal capillaries (this is the reason for neovascularization with bad CL)
O2 permeability formula
x 10^-11 (cm2/sec) x (mL O2/mL x mm Hg)
D is the coefficient of O2 movement
K is the solubility of O2
Dk/t minimums
- 87 x 10^-9 overnight swelling
- 125 x 10^-9 No overnight swelling
- 34 x 10^-9 for compromise (
Dk/t for no stromal anoxia with extended wear
75 to 125
SiHy vs hydrogel O2 Dk/t
-SiHy VERY close to being like not wearing a CL at all
Second generation SiHy
- AVO and AV advance
- need no surface treatment
- use PVP as a wetting agent
- intrinsically wettable
Third generation SiHy
- only use macromers
- no surface treatment
- no wetting agent
AO and biofinity
Stiffer SiHy lenses
-more silicone, more O2 transmitted
Methods of making CL
- Spin cast
- Lathe cutting
- Cast molding**
Spin casting
- original method
- liquid spun in mold
- polymerized with UV light
*could not determine BC
Rate of spin determines power:
more liquid towards edge is minus, less is plus
Lathe cutting
- Soft and GP lenses
- button of solid plastic cut to specific curves
- steeper, smaller and more minus
- lens hydrated to expand and flatten
- more expensive, less reproducible
- allows for BC selection
Cast molding
METHOD USED TODAY
- Liqud polymer injected between forms
- UV polymerization
- lens hydrated and packaged
*least expensive, highly reproducible
Big 4 companies and their specialties
- Alcon: O2
- B&L: Optics
- Cooper: wide range of products
- J&J: comfort
Manufacturer’s replacement recommendation for CL
-rule of thumb: it is the MAXIMUM
How long should patient’s be wearing their CL before they come into the office
4 hours
How often should you replace a CL case
3 months
Organic scratches
- scratch by a fingernail
- takes longer to heal
Chemical disinfection
Pros:
- convenient
- simple
- may increase compliance
Cons:
- preservatives
- soaking time
- cost
- some have little effect on acanthamoeba
most are max storage 30 days
Patients with sensitivity to polyquanternium
should not use BioTrue or Revitalens
Oxidative disinfection
- non preservative
- uses H2O2
Pros:
- rapid kill rate
- effective
- no preservatives
- cleans and bleaches
Cons:
- expensive
- SPK if not completely neutralized
- replace catalytic disc
- H2O2 decreases rapidly
Types: peroxiclear (4 hr) clear care (6 hr)
CL deposits
- Protein: white/opaque
- lipid: greasy
- jelly bumps: combo of protein and lipid
lipid is more common with SiHy because they adhere to silicone easily (few proteins)
protein more common with hydrogel (few lipids)
Surfactant Cleaners
- not used much anymore
- used for CL worn longer than 1 month
- rub lens and rinse it
Enzymatic cleaners
-use enzymes to break down proteins
How much stuff is removed with rubbing and soaking
> 90%
No rub lenses
-require 15 second stream of saline rinse
non-wetting surface
- increases deposits
- SiHy are more hydrophobic than hydrogels
bacteria most likely to cause SPK in CL wearers?
pseudomonas aeruginosa
Most common bacteria to cause SPK in non CL wearers
staphylococcus epidermidis
Gold star H2O2
3% to kill acanthamoeba
H2O2 disinfection time
- 3 hours in 3% to kill everything
- acanthamoeba can take 3 min to 9 hours
BUT need 4-6 hours to neutralize
Pt instruction if fit is not perfect
-tell pt to remove after 4 hours (this is when a problem will occur)
thermal conductivity of CL
-thicker lenses may feel hot due to decreased flow from the cornea
Lid adaptation to CL
- lids keratinize
- get stronger with more wear, specifically GPs
- sensitivity increases in 7 days, then decreases over the next 3 weeks
- if worn occasionally pt may never adapt, so they should wear them all the time for a while
CL rotation due to blinking
- CCW in right eye
- CW in left
lower lid moves in towards nose
How do eyes respond to decrease in O2 sleeping and CL wear
- 2-4% swelling in cornea upon awakening
- 5-8% with sleep – okay to wear CL
- 8-10% with sleep – questionable CL wear
Edema with soft/SiHy lenses vs GP
- soft/SiHy: overall edema; vertical striae lines
- GP: cloudy center, clear periphery
vertical striae
OCCUR WITH >5% EDEMA
- occur with soft/SiHy due to decreased O2 and corneal edema
- mistaken for nerves often
- nerves bifurcate
- pressure to globe will eliminate striae
spectacle blur
- blur that occurs for more than 15 minutes with GL after removing CL
- indicates edema
R/G duochrome
- Red clearer increase minus
- green clearer increase plus
GPC
giant papillary conjunctivitis
*Type I and IV hypersensitivity rxn
-seen with everted lids
-pt needs to clean lenses better
-autoimmune reaction to coatings on lens surfaces
OR
-mechanical irritation due to lens edge (ie GP lenses)
Signs:
early: papillae near tarsus not near margin
excessive lens movement and coating
papillae on tarsal plate
jelly bump
-lipids and mucin deposits
haze on CL
proteins
allows for microbial growth
vessel engorgement
Not really a problem
vessels engorge due to toxicity to increase O2 flow
fixes itself
Neovascularization
- more than 1 mm vessel growth into cornea
- vessels stay when cornea is fixed vs engorgement which goes away
corneal infiltrates
- inflammation usually near limbus for solution related problems
- hazy, white accumulations
risk factors:
-use multipurpose solution rather than peroxide**
-
microbial keratitis
-infection
risk factors:
- trauma
- poor CL hygeine
- immune compromised
Corneal ulcer
infection with excavation, infiltration and tissue necrosis
symptoms:
mucopurulent discharge
typically unilateral
Toric lens design options
- front toric
- back toric
- thin zone
- prism ballast
LARS
applies if greater than 10 degree but less than 20 degrees
Rotated to doctors left=add axis
rotated to doctors right=subtract axis
When to Rx toric lens
->0.75 D refractive astig
AND
->25% of sphere power of refractive astig
if only one is met, try SE first
toric CL OAD vs sphere CL
typically larger because the lens needs scleral support to stabilize
What will increase toric CL rotation
- tight lids
- high lower lid
- dried lens
Becherer Twist Test
sensitivity to axis fluctuations and rotations
- have sphere/cyl refraction in phoropter
- twist the best cyl correction until pt reports blur in vision
- determine # of degrees the cyl can be off axis without bluriness
*less than 5 degrees indicates high sensitivity and may not be a good candidate for soft torics (only
Order to select for CL
- Axis
- Cyl
- Sphere
*always round down for cyl power
Back surface toric CL
-better for pts with significant corneal cyl (about 2.00 D)
high modulus toric lenses
-hold shape better but rotate more
How to stablize torics
- prism ballast
- dynamic stablization with double thin zones
- accelerated stablization
- peri-ballast
- eccentric lenticulation
- back surface toricity
- reverse prism
- lid force holds lens in place
- watermelon seed: lid against cornea pushes CL down, increasing the mass to keep in place
Prism ballast
- bottom of lens thicker than top
- markings on inferior part of lens
- 1 to 1.5 prism diopters base down
Cons:
inferior discomfort
less O2 in thicker parts
Dynamic stablizations with double thin zones
- double slab off
- top and bottom are thinner
- thin zones interact with lids to stablize (dynamic)
- markings at 3 and 9
- vertical striae will be in center of lens because it is the thickest part
Pros:
more comfy due to thinner lens
Peri-ballast
- edge thickness equal at top and bottom
- thick above the edge of the lens
Dk/t for torics
- better to use average lens thickness
- WTR have lower avg than ATR in prism ballast
- hypoxia conditions more likely due to increased lens thickness
How to choose prism types
- corneal cyl: back surface toric more stable (CL doesn’t bend)
- spherical cornea: front surface toric
- tight lids: thin zone design (if VFW is 9mm and lids aren’t too tight)
- ATR cyl: prism ballast or thin zone
appropriate CL BC
flattest that is stable
average toric lens rotation
-5 to 19 degrees nasal (CCW for OD, CW for OS)
Bad fit toric lens
rotation greater than 20 degrees
Compensated toric lenses
- lens will still have the markings away from 6 position, but you compensate for the lens rotation by giving the pt a new axis
- usually improves VA by about 1/2 line (20/25+ to 20/20)
induced cylinder power
- 1/2 the contact lens cyl when rotated 15 degrees
- ie -1.00-2.00x018 rotated 15 degrees induces -1.00 cyl
Visual success of CL
- within one line of spectacles
- if within two, use best judgment
- List 5 causes of reduced vision with SiHy lenses. (page 2, slide1)
a. Lens deposits (usually lipid)
b. Lenses could be switched (right and left)/incorrect prescription
i. How can you tell they are switched?
1. Over-refraction would be equal but opposite
ii. Re-instruct them to insert right lens first then the left one to avoid switching them accidentally
c. Uncorrected refractive error (especially if you used spherical lenses and they had residual cylinder present)
i. How do you determine the un-corrected refractive error?
1. Balanced over-refraction
d. Toric lens rotation
e. Damaged/defective lens
f. Lens inversion= flipped the lens inside out
i. Least common
- What should you do if deposits are visible on the lens? (page 2, slide 3)
a. Protein deposits
i. Change to a solution with additional sequestering/chelating
ii. Consider Rewetting agents with cleaning action
b. Lipid deposits
i. Address lid hygiene
ii. Change to a product with more surfactant
iii. Consider adding a separate surfactant cleaner
c. For both, consider frequency of replacement
d. Review rubbing the lens with the patient
- What can cause vision to be reduced with lenses off? (page 2, slide2)
a. Corneal hypoxia or infection
- What is cause of OR being same value, opposite sign? (page 3, slide 1)
a. Lenses are switched between the eyes
- How do you treat spectacle blur? (page 3, slide 2)
a. Def- blur even after you have had your contacts off for 30 minutes
b. Tx= change material to increase oxygen, change stabilization method, reduce wearing time
c. To determine if they have it, make sure the pt’s glasses are their current SRx and not an old one.
- List 5 causes of lens discomfort. (page 3, slide 3)
a. Damaged lenses
b. Deposit or debris on lenses
c. Solution sensitivity
d. Corneal abrasion/ulcer/staining
e. Infection
f. Poor fit
g. Corneal edema
h. Trapped foreign body
i. Improper solution use
- What’s the usual cause of a central lens defect? (page 4, slide 1)
a. Improper/aggressive removal of the lens
b. Action should be like picking lint off a sweater
- What’s the usual cause of a lens edge defect? (page 4, slide 1)
a. Defects
i. Case-dependent/related
- List 5 causes of lens dryness (page 4, slide 3)
a. Poor tear quality or quantity
b. Solution sensitivity
c. Medication related
d. Pregnancy
e. Computer use/lack of blinking
f. Systemic disease
g. Environmental conditions
h. CL material type
- List 5 treatments for lens dryness (page 5, slide 1)
a. Solution that provides wettability
b. Hydrogen peroxide care system
c. Lens material with increased wettability
d. Lens lubricants
e. Lid scrubs
f. Fish oil supplements
g. Punctal plugs
- List 3 reasons for excessive lens movement (page 5, slide 2)
a. Flat lenses, deposited lenses, inverted lenses
b. Example: patient is wearing an 8.6 BC and need a tighter fit= put them in an 8.4
c. Inverted lens= remove and flip it the right way
i. Re-teach them the proper way to put the lens on
1. TACO test
- What is the purpose of blinking?(page 7, slide 2)
a. Maintain pre-corneal tear film, remove intrinsic and extrinsic matter, facilitate tear exchange
- List 5 complications of abnormal blinking
a. Visual degradation= pt can’t see as well/vision is reduced
i. Some parts of the lens is wet and other parts are dry so not looking through the same medium throughout the lens
b. Prolonged lens settling
c. Epithelial dessication
d. Post-lens tear stagnation
e. Hypoxia
f. Soft lens staining
g. Lens surface drying and deposition
i. Use artificial tears
- List 5 signs and symptoms of GPC (page 9, slide 2)
a. Signs
i. Papillae on tarsal plate
ii. conjunctival hyperemia
iii. excessive lens movement
iv. excessive lens coating
b. Symptoms
i. Feel the lens/lens awareness
ii. Itching
iii. Blurry vision
iv. Mucous strands/coated lens
v. Dry eye
- Describe the mechanical cause of GPC (page 10, slide1)
a. With each blink, the antigen-coated lens mechanically traumatizes the tarsal conjunctiva which causes release of mediators
- Describe the immunological cause of GPC (page 10, slide 1)
a. Antigen recognition and events leading to increase in IgE, IgG and C3 in tears. These factors interact with the mediators released by trauma, causing release of vasoactive amines
- List 5 antihistamine/mast cell stabilizer drugs (or combos) for GPC (page 10, slide 3)
a. Olopatadine 0.1 or 0.2%
i. Patanol, Pataday
b. Epinastine HCl 0.05%
i. Elestat
c. Lacaftadine
i. Lastacaft
d. Bepostastine
i. Bepreve
e. OTC Zaditor, Alaway
- List 2 ‘soft steroids” for GPC (page 10, slide 3)
a. Loteprednol 0.5%
i. Lotemax
1. Coupons available to help with cost
b. Loteprednol 0.2%
i. Alrex
- What is & how do you treat mild (stage 1-2) GPC? (page 11, slide 1 and page 12, slide 1)
a. Mild to moderate mucus discharge, itching, mild CL coating, blurred vision after hours of wear
b. Tx= nightly ocular irrigation, more frequent lens replacement and cleaning, mast cell stabilizer/antihistamine
c. Can they still wear lenses with GPC?
i. Technically yes, but it will heal better if they don’t wear their lenses for awhile
- Describe stage 3 GPC and the treatment. (page 12, slide 2 and page 13, slide 1)
a. Moderate to severe mucus discharge, variable itching, increase in lens movement, moderate blurring of vision, conjunctival erythema and edema, papillae
b. Tx= no lens wear, irrigation, steroid, mast cell stabilizer, anti-allergy, antibiotic if corneal staining
- What is the cause & Tx of arcuate staining? (page 15, slide 2)
a. Corresponds to lens edge, may be 2-3mm from limbus
b. soft and GP wearers are affected
c. tx (on page 21, slide 1)= high water change to thicker lens or lower water design, silicone hydrogel change to HEMA, increase replacement frequency, discontinue wear until healed
i. can use ATs to help with dryness while healing
- Cause & TX of redness & compression staining. (page 17, slide 1)
a. Compression staining is due to a tight fight
i. Tx= find a better fitting lens or change to a lens with a different edge design
b. If redness occurs:
i. Immediately upon insertion then cause:
1. Toxic or atopic response to solution
2. Treatment options:
a. Change to a preservative-free care system, change to a system with a different preservative or lesser concentration of that preservative, add a saline rinse
ii. At the end of the day
1. Causes: lens dehydration or deposition
2. Tx= add rewetting agents with or without cleaning action, consider different lens material group
