Lens Modification Flashcards
What modifications ARE possible on RGPs?
DD Often Show Pretty Flowering Posies At Events.
Limited power change
Increase or flatten peripheral curves
Reduce: diameter, optic zone, sagittal depth
Alter edge design
What modifications are NOT possible on RGPs?
Little Princess Don’t Step Pretty in Dung, Often Slippery Because Creamy.
CAN NOT :
Large power changes
Decrease or Steepen peripheral curves
Increase: diameter, optical zone, sagittal depth
Alter of Base curve.
POWER: Using the Lensometer to determine power with soft lenses:
Blot with lint free tissue so free of water, but not so dry as to shrink the lens. Concave side down.
DIAMETER; V-Gauge how to measure total diameter:
clean, dry contact lens and clean dry gauge. place lens near the top and tilt the gauge aprox 60 deg and tap the gauge on the counter. the diam is read off the gauge at widest point. Do NOT force.
Diameter: Reticle Magnifier, how to use:
Contact must be dry. Place contact on hold up to light, read markings. (can see other curves also)
Other use for Reticle Magnifier:
To examine the edge of a RGP turn the magnifier around so you are looking through the end containing the scale. This will move the focal plane away from the magnifier so you can view the edge of the lens in profile.
When “evaluation the edge we are looking for:
Contour (thickness, sharpness, edge lift) cracks or chips.
BASE CURVE: How to use the Radiuscope:
Contact must be dry and clean. Add drop of solution and put in contact (concave up) inside must remain dry. Take the lens from the lowest position where the star (real image) is visible, Set scale to ZERO
Raise to higher star target (aerial image), focus sharply
Read scale.
Using radiuscope for toric base contact:
same as spherical except:
Turn mount in circular direction until one of the “spokes” is clearer and continuous along its entire length. (bottom)
Bring up (aerial view) and get same “spoke” clear.
Read scale. Record
Using the FINE FOCUS knob, focus sharply on the spoke 90 DEG AWAY from the first and read curve.
How do you read the scale on the radiuscope:
The gauge is read like a clock. the small hand is the hundreds and it is read on the inside scale: the large hand is the tens and ones, read on the outside scale. 7.92, the small hand will be at the 8 (just before), read on the inside scale, and the large hand will be at 92, read on the outside scale.
DESIGN: Identifying toric lenses:
To check if toric you need to check power on the lensometer and the base curve on the Radiuscope.
Power will show if toric in radiuscope.
Curvature would show two distinctly different curves.
A Back Surface or Bitoric lens is identified by:
Showing toricity on the Radiuscope AND lensometer
A Front Surface toric is identified by:
Showing toricity on the lensometer but not on the radiuscope.
A warped lens is identified by:
Showing toricity on the radiuscope but NOT the lensometer.
What will a flat lens look like in Fx:
Bearing in the middle (dark)surrounded by clearance (bright)
Darkness indicated pressure on the cornea
Smaller darker areas mean even greater deg of flatness
Large amts of movement and de-centration
Lining caused a lot of movement and lens is dropped inferiorly if too flat.
How to correct a flat lens:
Increase the diameter first
Steepen the base curve
Don’t forget to adjust the power to correlate with the changes.
What will a steep lens look like with Fx:
Central area of clearance
More comfortable because they fit tighter to the cornea
Lack of lens movement
Good initial comfort, but complaints of blurry vision or redess and irritation by the end of the day.
Centers well
How to correct a steep lens:
Decrease the diameter first
Flatten the base curve
Adjust the power to correlate with he changes
What pattern should show in the Fx with perfect With the rule alignment?
Classic dumbbell pattern
Flat lens on a with the rule cornea will look like:
A dark flat cookie
A steep lens on a With the rule cornea will look like:
dark ( ) parenthesis
What pattern should show in the Fx with perfect Against the rule alignment?
Classic hourglass pattern
Flat lens on an Against the rule cornea will look like:
a cat pupil (oblong running up and down)
A steep lens on an Against the rule cornea will look like:
turned parenthesis on top and bottom
Why is increasing diameter preferred a first step in modification?
Larger lenses tend to be more comfortable and more stable than small
