7 - Contacts2 Flashcards
Aspheric design
Flattens toward the periphery - mimics cornea
Better centration and comfort
Decr magnitude of spherical aberrations
Primary disadvantage = decr tear exchange
Multifocal GPs
- simultaneous design
- translating design
S: both D + N located within pupil at same time
- centration is critical
- like PAL
T: segmented
-like flat-top BF
Super basic difference bw flexure and warpage
F = on eye only
W = on or off eye
Flexure
-factors that incr (5)
THINNER center thickness More CORNEAL ASTIGMATISM (1.50 or more) INCR OZD = incr sag = incr flexure Material - HIGH/HYPER DK materials STEEPER BC
Flexure
-who will tend to have lenses that maintain shape/resist flexure
Hyperopes/plus GPs
Myopes/minus GPs with center thickness >0.13mm
Flexure
-how you find/measure
Keratometry
-if read toric = flexure
Flexure
-when it can actually be helpful
May minimize residual astig in pts with WTR astig
-counteracts the avg internal lenticular astig of -0.50 x 090
Warpage
- main cause
- effects
Excessive digital cleaning
Modifies BC -> alter magnification, incr effects of marginal astig
GP gas permeability
P = Dk
Permeability = diffusivity of the gas in the material * solubility of the gas in the material
High Dk (51-99) = recommended for extended wear (also hyper (100+) Low Dk (25-50) = can be used for daily wear
Calculating total amount of gas that actually passes thru a lens
Transmissivity = Dk/t
Where t is thickness of lens in cm
Soft lenses
-which surface is usually toric
Front
Soft lenses
-stabilizing techniques (5)
PRISM BALLASTING - BD prism at the bottom, greater amount for small diameter, low refr power (thin edges)
PERIBALLASTING - BD prism at bottom outside optic zone only -> decr edge thickness, improved optics
DYNAMIC STABILIZATION - thinning of superior + inferior portions -> thicker horizontal meridian
ECCENTRIC LENTICULATION - periballasting + dynamic stabilization
TRUNCATION - more of a GP thing
Soft lenses
-describe LARS
Left add, right subtract for axis
From dr’s POV and at 6:00 position
-if 12:00, reverse
Adjustments are made from SRX, not CLS
Soft lenses
-how to pick diameter of lens
HVID + 3mm
Ensures 1.5mm extension beyond limbus for 360 degrees
Soft lenses
-gas permeability
—traditional hydrogel vs silicone hydrogel
TH: incr water = incr Dk (high permeability)
SiHy: incr water = decr silicone = decr Dk (low permeability)
-silicone transports O2 more quickly than water
Soft lenses
-FDA classifications (ions, water)
1) Low water, Non-ionic
2) High water, Non-ionic
3) Low water, Ionic
4*) High water, Ionic
5) silicone hydrogels
*group 4 is most likely to have deposits
Soft lenses -rigidity/stiffness —modulus —thickness —water
Incr stiffness with:
- incr modulus
- incr thickness
- decr water
Soft lenses
-benefits of high-modulus sihy lenses (3)
Better handling
Easier application/removal
Easier to determine if it’s inside out
Soft lenses
-drawbacks of high-modulus sihy lenses (5)
GPC (giant papillary conjunctivitis) SEAL (superior epithelial arcuate lesions) LEH (limbal epithelial hypertrophy) Mucin balls Edge fluting
Contact lenses vs spectacles
-accommodation of hyperopes vs myopes
H accomm less with CLS
M accomm MORE with CLS
Contact lenses vs spectacles
-magnification of hyperopes vs myopes
H have smaller mag with CLS
M have MORE mag with CLS
Contact lenses vs spectacles
-convergence of hyperopes vs myopes
H converge less with CLS
M converge MORE with CLS
