week 3 Flashcards
Name one or two examples of aspheric CL brands:
Frequency 55 Aspheric
– Biomedics 55 Premier / Avaira
– PureVision / PureVision2
– Definition AC
soft toric lenses often work well for patients with what kind of astigmatism?
Soft lenses often work well for patients with lenticular
astigmatism and ATR corneal cyl
For ATR corneal astigmatism in soft toric lenses, what kind of decentration is common
lateral decentration is common
For lenticular astigmatism, what is the best type of toric lens?
For lenticular astigmatism, a front surface toric GP is required
Soft Toric Lenses work best for patients with how much astig?
Soft Toric Lenses work best for patients with moderate
refractive astigmatism
T/F: The less the cylinder component is compared to the
spherical component, the better the results
True
Higher myopia correlated with less stability in what kind of designs of toric lenses?
Higher myopia correlated with less stability in prism
ballasted designs
Lower myopia correlated with less stability in what kind of designs of toric lenses?
Lower myopia correlated with less stability in double
slab-off designs
What are the 3 most influential characteristics on lens
stability:
1) Palpebral aperture size
2) Degree of myopia
– Higher myopia correlated with less stability
3) Lid angles
what palpebral aperture size corresponds to greater stability?
Smaller PA correlated with greater stability
what is a positive intercanthal angle and what kind of rotation is it associated with?
Positive angle=temp lid higher than nasal
- correlated with temporal rotation
- *Positive angle more common
what are some of the tolerances and success rates of cyl axes of 20, 15, 10 and 5 degrees?
- Rotation± 20- success rate is 90% for soft torics
- Rotation± 15- success rate is 90% with 2 lenses
- Rotation± 10- success rate is 70% with 3 lenses
- Rotation±5- Patient must accept variable vision with soft torics
where are the thickest edges on a toric WTR soft CL? ATR? oblique?
• WTR: thicker edge at top and bottom
• ATR: thicker edge at nasal and temporal
• Oblique: thicker edge along more minus meridian
• For all: greater edge thickness with greater
myopia, which interacts more with eyelids
T/F: In most modern designs, toricity is limited to the optic zone so that it does not affect the fit or rotation of the lens when on the eye
true
what is prism ballasting?
incorporating 0.75–2.00 D of base down prism into the CL
what is peri-ballasting?
Peri-ballast incorporates prism in peripheral (carrier) portion only, so no optical prism effect. Most modern designs do this instead of full prism ballast
what is the “Watermelon seed effect”?
if a moist, rounded-off wedge is squeezed, it will be expelled towards its base down direction
Acuvue Advance/Oasys for Astigmatism use what method for prism stabilization?
“Accelerated Stabilization Desig”
-Active zones (thicker middle zones that force lens into place when acted upon by lid)
what is eccentric lenticulation?
[method for stabilizing lens] a front surface off center (eccentric) lenticular cut in the direction of the prism apex
T/F: markings on a toric lens indicate the location of the cylinder axis
FALSE
cyl power comes in what power steps generally for standard soft toric lenses?
0.50 D
which is more important for fitting soft torics: the refractive cylinder or the corneal toricity
The refractive cylinder, not the corneal toricity, is the primary concern for fitting soft torics
T/F: The higher the refractive sphere correction, the
greater tolerance for uncorrected cylinder
True
In general, soft toric lens should not rotate more than __
degrees
15-20 degrees
If so, another base curve or lens design should be tried
Lens should not rotate more than –° during the blink
Lens should not rotate more than 5 to 10° during the blink
What is the Challenge test to assess Assess rotational stability?
Challenge test: manually rotate lens to off axis position and see how long it takes to return to original position
**should be less than 30 seconds
