Week 3 - Fitting Soft Contact Lenses Flashcards
Inserting contact lenses adversely affect tear lens (change how the tears work).
What 4 changes to do with CLs and fitting CLs can cause this?
- Contact lens surface/ design
- Tear of wearer
- Drops / saline solution
- Indicates px suitability
What 4 things do you do during the slit lamp evaluation?
-overall view of eye - sit lamp illuminations
-tarsal plate assessment (lid eversion)
-FBUT (fluorescein break up time)
-choose appropriate lens design
What do we need to consider when choosing the appropriate lens design? 3
-material (DK/T value)
-lens design (BC/Diameter)
-surface of the lens (surface coats which affect dry eye)
If power is under +/- 4.00D it does not need to be vertexed. T/F
TRUE
what are the 4 steps to designing a soft contact lens?
- Make sure prescription is in MINUS FORM.
- Draw optical cross
- Vertex Lens
- Determine power, base curve and diameter
Determine is the soft contact lens requires a toric or sphere.
What are the 2 conditions?
- The sphere: cyl > 3:1 - the sphere power is greater than or equal to 3 times the cyl power.
- CL RX cyl is < -1.00D - the cyl power is equal to or less than -1.00D.
If both conditions exist then we use a spherical equivalent if NOT go to soft toric
After -/+6.00D the steps go up in 0.50 D increments. T/F
TRUE
-6.50D to -12.00D
+6.50D to +8.00D
BE CAREFUL IN TESTS AS WILL TRY AND TRICK
Toric options for contact lenses are usually found in these powers ………. (5)
-0.75
-1.25
-1.75
-2.25
-2.75
What is the rule of thumb when considering the diameter of a contact lens?
the contact lens should fit 1mm larger than the cornea (overlapping the limbus) although often we are bound to what the manufacture makes
What is the common diameter ranges ?
14.00 mm to 14.50 mm
For a steep cornea, if there is only one BC option should we chose the larger diameter or smaller diameter lens?
Smaller -
the steeper the cornea the smaller the diameter = larger saggital depth
the flatter the cornea the larger the diameter = smaller saggital depth
What do most Base Curves come in? (range)
8.2 - 9.0 mm
The steeper the keratometer reading the lower the base
curve number. T/F
TRUE
BC for steep K (OVER 45.00D) reading?
8.3mm
BC for medium K (42.00D to 45.00D) reading?
8.6mm
BC for flat K (UNDER 42.00D) reading?
8.9mm
What vertex distance do we assume if nothing is specified?
12mm
ALWAYS use an optical cross to determine what CL rx is needed when cyl is present. T/F
TRUE
What material has dominated the CLs market?
Silicone Hydrogel
What are 2 ways to increase DK (oxygen permeability) in a HYDROGEL lens?
- Decrease lens thickness.
- Increase water content.
How is oxygen transported through a HYDROGEL lens?
Through the water channels
What are the 4 groups of material for hydrogel?
- Lower Water content & non-ionic polymers
- High water content & non-ionic polymers
- Lower Water content & ionic polymers
- High water content & ionic polymers
If the K readings have a difference of more then or equal to 2.00D what do we recommend?
Rigid Gas Permeables
More Water Content = more breathable lenses as more oxygen transmission T/F
TRUE
What is a benefit of the Night and Day Lenses (Lower Water content & non-ionic polymers) ?
generally show lower levels of protein deposits
What do you not want to use with the Proclear lens (High water content & non-ionic polymers) ?
sorbic acid found in certain solutions might cause discoloration
What can happen with a Acuvue (High water content & ionic polymers) ? 2
-Highest level of protein deposit
-avoid sorbic acid as
disinfectant due to discoloration
What can happen with a PureVision lens (Lower Water content & ionic polymers)? 2
-Balance Oxygen permeability and durability
-more protein deposits
Ionic polymers are more sensitive to temperature and the composition of care products. T/F
TRUE - they also attract higher levels of deposits from tears
Does a low water content lens have a longer lifespan and less breakage?
YES
What is the disadvantage to a low water content lens?
less breathable lens - more chance of vascularization
The high water content materials have faster adaption with comfort and wearing time. T/F
true
What is a disadvantage to high water content materials? 4 (lifespan/stability/issues?2)
- shorter lifespan
-more deposits
-dry eye issues
-less stable
What are the advantages of THIN HYDROGEL LENSES? 4 (conditions 3/patient)
- Lower incidence of edema
- Reduced lid sensation because of thinner edges
- Reduced limbal irritation because of thinner edges and
larger total diameter - Safer if the patient falls asleep
What are the disadvantages of a THIN HYDROGEL LENSES? 5 (handling, breakage, lifespan, vision, effect on eye)
- Handling is more difficult
- Higher breakage rate then standard thickness lenses
- Shorter life span
- VA may not be as sharp with toric corneas
- Dehydrates on eye
What group does Silicone Hydrogel fall into?
FDA Group V - five
What are advantages of Silicone Hydrogel lenses? 2 (adaption/good for who?)
-high Dks with rapid adaptation
-good for patient with vascularization and mild dry eyes.
What are disadvantages of Silicone Hydrogel lenses? 2 (conditions?3)
-greater incidence of GPC and arcuate
staining in certain materials
-more likely to have mucin balls
The lower the Dk value the less breathability. The more the DK value the more breathability. T/F
TRUE
How do we now if a lens is well fitting? 3
- Good centration with full corneal coverage in all direction of gaze
- Sufficient movement to allow tear exchange under the lens during the blink (0.1 to 0.5 mm is generally
considered optimal) - Satisfactory Push-Up Test
What is a tight fitting lens also known as?
Steep Lens fit
What is a loose fitting lens also known as?
flat Lens fit
When a contact lens is too tight or too steep what should we expect from the movement of the lens during blinking?
insufficient/ no movement during the blink in primary or upward gaze
How will a tight lens react in the push up test if it is too tight? 3
- resist movment
- on upward nudge the lens may remain decentered
- on upward nudge the lens may return slowly to its orginal position
What are 6 signs and symptoms of a tight/steep fitting lens? (centration/comfort/vision3/physical sign)
- Good centration
- Good comfort
- Fluctuating vision between blinks
- Poor visual acuity
- Temporary improvement on blinking
- Blanching/ lens indentation
When a contact lens is too loose or too flat what should we expect from the movement of the lens during blinking?
Excessive lens movement during the blink in primary or upward gaze
How will a loose lens react in the push up test if it is too tight? 2
- Lens will readily move
- Lens may drop back inferiorly quickly
What are 6 signs and symptoms of a loose/flat fitting lens? (comfort/ centration2/ vision2/ physical sign)
- Vision may be blurred after the blink
- Comfort of fit is poor
- Poor centration
- Post blink movement is >0.4mm
- Peripheral edge standoff
- Vision is variable
What could a loose/flat fitting lens be mistaken for?
Inverted lens - check to see if the lens is inverted if signs and symptoms of a loose lens occur.
What can happen to the edges of a loose/flat lens?
edge stand off
What can happen to the edges of a tight/steep lens?
conjunctival indentation
After the characteristics of a well-fitted lens have been satisfied
* Conduct a spherical over-refraction to determine the proper lens power to be dispensed. T/F
TRUE
What is the relationship between saggital depth, and steep/looseness of a contact lens?
Saggital depth –
-greater the depth of the lens - the steeper the lens
- the lower the depth of the lens - flatter the lens
When over refracting what prescription do we start with?
Plano - +0.25D
then
Plano- -0.25D
If we keep the BC the same what do we do to the diameter to steepen the fit?
to steepen the fit we select a larger diameter
If we keep the diameter the same what do we do to the BC to steepen the fit?
to steepen the fit we select a smaller BC
If we keep the BC the same what do we do to the diameter to flatten the fit?
to flatten the fit we select a smaller diameter
If we keep the diameter the same what do we do to the BC to flatten the fit?
to flatten the fit we select a larger BC
