Review of CL I and II Flashcards
Which type of optics has a varying curvature across the surface of the lens to counter spherical aberration
Aspheric optics
What are the 2 types of BCL?
acuvue oasys, air optix night and day
What must the power of the lens be to be considered a true BCL?
plano
is the Dk of SiHy >/< Hydrogel?
SiHy > Hydrogel
Since SiHy has a higher Dk, what type of lenses is it used in?
extended wear lenses
What happens to the following properties of a hydrogel contact when water content is increased?
* durability
* Dk
* deposit formation
* dry eye symptoms
All increase except for durability
What happens to the Dk of a SiHy contact when the water content is increased?
decreases; silicone content is what increases the oxygen permeability
A low/high modulus resists deformation, holds shape better, is easier to handle and provides better visual acuity
high
Does a low or high modulus lens experience more edge lift, fluting, superior epithelial arcuate lesions, mucin balls, GPC?
high modulus
How do we determine the diameter of a SCL?
HVID + 2
What happens to the sag height of a SCL as the diameter increases assuming a fixed base curve radius?
increases
Which BC do we start with when fitting SCL if there is more than one available?
steep
Is LARS calculated from the patient or doctors perspective?
doctor’s perspective
Fill in the blanks
A. Spherical RGP
B. Front Toric RGP
C. Back Toric RGP
D. Bitoric RGP
E. SPE Bitoric
F. CPE Bitoric
A GP lens moves along the direction of most/least resistance
least
Where is the GP lens the loosest?
Where the cornea is the steepest
How much movement is normal in a GP lens?
1.0-1.5 mm
How do you increase edge lift of a GP lens?
increase PC width (must narrow OZD or increase OAD)
For every _____ mm change in BC, you must change the power by ______ D
0.10 mm; 0.50 D
What are the clinically meaningful parameter change values for BCR, OAD/ OZD, PCR, PCW and CT?
- BCR: 0.1 mm (0.50 D)
- OAD/ OZD: 0.3 mm
- PCR: 0.5 mm
- PCW: 0.2 mm
- CT: 0.02 mm
How is SPE bitoric special in regards to rotation?
Vision is unaffected by rotation of the lens on the eye; acts like a spherical lens- can rotate while centered
When does residual astigmatism occur?
When refractive astigmatism does not equal corneal astigmatism
What is unique about writing the prescription for a back toric GP?
Only have to specify power in the most plus meridian
When might you need toric peripheral curves?
When edge lift is not equal but it is symmetric
How is a front toric GP stabilized?
BD prism (0.75-2.00 BD); can truncate if a slight adjustment is all that’s needed
What Dk do you order if prism is added?
higher Dk
What does simultaneous aspheric mean in regards to multifocal contacts?
change in power from center to periphery; SCL: center near or center distance; GP: mainly center distance
Who are the best candidates for aspheric GP’s?
low lower lid (and/or loose lids); smaller- average pupil size; low-medium adds; critical vision not essential; computer; athletes
Which aspect of fit is critical when fitting aspheric GP’s?
centration; optics should be over the pupil
What should be modified if the aspheric GP is decentered or moves excessively?
steepen base curve (0.10 mm); or increase lens diameter (0.50 mm)
Which type of GPs are segmented like bifocal glasses and use prism ballasting to promote proper orientation?
translating
Where should a translating GP rest in primary gaze?
on or near the lower lid
What amount of nasal rotation may be helpful for reading?
<15 degrees
Where is the segment line on a translating GP?
at or near lower pupil margin
