UNIT FIVE - GP Flashcards
What are the three lens design goals necessary for GP lenses?
Optical ( clarity & stability)
Physiological ( maintain ocular integrity)
Comfort
What are some key factors when looking at the optical design goal for GP lenses?
Good centralization Minimum post blink movement Adequate optical zone Minimum lens flexure Deposit resistance
What are some factors when looking at the physiological design goal for GP lenses?
Adequate transmissibility
Sufficient movement ( waste products & oxygen
Minimum corneal bearing
What are some factors when looking at the comfort design goal for GP lenses?
Minimum lid interaction
Tear layer thickness ( Vault)
CPC (B.C. Radius)
POZ diameter
Power of Tear layer ( lacrimal lens)
SAM - steeper add minus
FAP - flatter add plus
What does the acronym SAM stand for?
Steeper add minus
( when referring to the lacrimal lens or power of tear layer) 
What does the acronym FAP stand for?
Flatter add plus
(when referring to the lacrimal lens or power of tear layer)
Why is a peripheral curve necessary?
Allows fresh reservoir of tears to collect around the lens between blinks.
Allows tear exchange between blinks.
Permits lens to glide over flatter peripheral regions of cornea.
What are some of the determining factors for peripheral curves?
Lens diameter, POZ diameter, CPC radius, corneal shape.
What does center thickness effect?
Transmissibility
Centering and movement (gravity)
Lens Flexure
Edge Thickness (hyperflange, myoflange) 
What are some of the determining factors for center thickness?
Prescription
Lens diameter
Lens material
Lens design
What are the General rules for rigid lens design? (3 total)
CPC OR BC
1) as the degree of astigmatism increases, a steeper base curve is needed for centralization.
2) as the size of the OZ increases, The CPC must be made flatter to maintain the correct vault.
3) increasing the vault causes the lens to fit tighter and reduces movement.
What are the General rules for rigid lens design? (3 total)
LENS DIAMETER
1) large (11.5mm), flat (<42.00D) corneas require large lenses.
2) Large palpebral apertures (>10mm) require larger lenses.
3) less than a +2mm upper lid position may require a larger lid attachment design or an inter-palpebral design.
What are the General rules for rigid lens design? (2 total)
OPTICAL ZONE DIAMETER
1) large pupils (>4mm) require larger optical zones.
2) the optical zone usually varies with the lens diameter.
What are the spherical rigid power rules ? (5 steps)
1) Transpose into - cyl
2) compare RX cyl to K readings and calculate residual astigmatism
3) if residual astigmatism is 1.00D or less, IGNORE. (CAP)
4) compensate for vertex is > +/- 4.00D
5) compare CPC in diopters to flat K and adjust power by difference (FAP or SAM)
SPHERICAL RIGID LENS POWER RULES EXAMPLE !!!!
Rx: -3.00 +1.00 x 090
K reading: 42.00/43.00 @90
1) Convert to - cyl:
- 2.00 -1.00 x 180
2) Both RX and K are at 1.00 WTR ( difference between 43 and 42) ( -1.00 cyl @180)
3) CRA (residual astigmatism) is the difference between 1.00 WTR for both so 1.00-1.00= 0 CRA
4) CPC = 0.50D steeper than Flat K (flat K is 42) so CPC= 42.00+ 0.50 = 42.50
5) order lens power : -2.50 ( 0.50 steeper than -2.00)
Paragon spherical GP design steps
1) lens diameter
2) CPC or BC
Paragon Nomogram:
Use the nomogram to find the correct Lens diameter for:
K: 42.00/42.50@90
9.0–9.5 mm
If flat K is 42.00D, The guide indicates a diameter of 9.0–9.5 mm
Paragon Nomogram:
Use the Nomogram to determine the CPC or BC for:
K: 42.00/42.50@90
Corneal cylinder: 0.50D
Diameter: 9.0-9.5mm
Flat K or 0.25D steeper
(first you must find the diameter in millimeters based off the flat is K, then you must find the corneal cylinder. Based off of those two numbers, the monogram shows the guided recommendations for the spherical GP design.)
Summit Aspheric Periphery Design:
Using the summit table, convert BC to radius of curvature of:
K: 42.00/42.50@90
Corneal cylinder= 0.50D
8.08mm
First find the initial BC: 42.00 - 0.25: 41.75 (0.25 flatter than K) Use the formula to convert: r=337.5/D r=337.5/41.75 r=8.08mm
What are the three steps for diagnostic lens fitting?
1) Select diagnostic lens (CPC, POZ, and diameter are most important. Power should be within +/- 2.00D of Rx)
2) Inspect & Insert diagnostic lens.
3) Evaluate position & movement. (Interpalpebral and lid attachment)
For diagnostic lens fitting, what should the power parameters be within?
+/- 2.00D of RX
What are the steps when we are evaluating the lens and corneas relationship?
1) install fluorescein ( add color)
2) check the lens periphery
3) check for corneal patterns/CPC
(Alignment, steep, or flat)
4) problem solving
What is the point of using fluorescein when evaluating the lens and cornea relationship?
The use of color or fluorescein can detect corneal patterns.
( alignment, steep, or flat cornea)
What type of attachment is this ?
Lid attachment
What type of attachment is this?
Interpalpebral
What type of attachment is shown ?
Alignment GP pattern Spherical cornea
Looks smooth
What type of attachment is shown ?
Steep GP Pattern Spherical Cornea
What attachment is shown here ?
Flat GP pattern spherical cornea
What type of attachment is this?
Alignment WTR
What type of attachment is shown?
Steep WTR
What are some problems that need solving when it comes to contact lenses?
Tight lens No movement Loose lens Low/high riding lens 3-9 staining Flare Poor VA (Flexure)
PROBLEM SOLVING BREAKDOWN SHEET
What kind of problem does this image show ?
Low riding / loose
What kind of problem does this image show ?
3:00 & 9:00 staining with Dellen
What kind of problem does this image show ?
Flare
