7 - Contacts2

Question 1

Aspheric design

Answer 1

Flattens toward the periphery - mimics cornea

Better centration and comfort
Decr magnitude of spherical aberrations

Primary disadvantage = decr tear exchange

Question 2

Multifocal GPs

• simultaneous design
• translating design

Answer 2

S: both D + N located within pupil at same time

• centration is critical
• like PAL

T: segmented
-like flat-top BF

Question 3

Super basic difference bw flexure and warpage

Answer 3

F = on eye only

W = on or off eye

Question 4

Flexure

-factors that incr (5)

Answer 4

THINNER center thickness
More CORNEAL ASTIGMATISM (1.50 or more)
INCR OZD = incr sag = incr flexure
Material - HIGH/HYPER DK materials
STEEPER BC

Question 5

Flexure

-who will tend to have lenses that maintain shape/resist flexure

Answer 5

Hyperopes/plus GPs

Myopes/minus GPs with center thickness >0.13mm

Question 6

Flexure

-how you find/measure

Answer 6

Keratometry

-if read toric = flexure

Question 7

Flexure

-when it can actually be helpful

Answer 7

May minimize residual astig in pts with WTR astig

-counteracts the avg internal lenticular astig of -0.50 x 090

Question 8

Warpage

• main cause
• effects

Answer 8

Excessive digital cleaning

Modifies BC -> alter magnification, incr effects of marginal astig

Question 9

GP gas permeability

Answer 9

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

Question 10

Calculating total amount of gas that actually passes thru a lens

Answer 10

Transmissivity = Dk/t

Where t is thickness of lens in cm

Question 11

Soft lenses

-which surface is usually toric

Answer 11

Front

Question 12

Soft lenses

-stabilizing techniques (5)

Answer 12

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

Question 13

Soft lenses

-describe LARS

Answer 13

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

Question 14

Soft lenses

-how to pick diameter of lens

Answer 14

HVID + 3mm

Ensures 1.5mm extension beyond limbus for 360 degrees

Question 15

Soft lenses
-gas permeability
—traditional hydrogel vs silicone hydrogel

Answer 15

TH: incr water = incr Dk (high permeability)

SiHy: incr water = decr silicone = decr Dk (low permeability)
-silicone transports O2 more quickly than water

Question 16

Soft lenses

-FDA classifications (ions, water)

Answer 16

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

Question 17

Soft lenses
-rigidity/stiffness
—modulus
—thickness
—water

Answer 17

Incr stiffness with:

• incr modulus
• incr thickness
• decr water

Question 18

Soft lenses

-benefits of high-modulus sihy lenses (3)

Answer 18

Better handling
Easier application/removal
Easier to determine if it’s inside out

Question 19

Soft lenses

-drawbacks of high-modulus sihy lenses (5)

Answer 19

GPC (giant papillary conjunctivitis)
SEAL (superior epithelial arcuate lesions)
LEH (limbal epithelial hypertrophy)
Mucin balls
Edge fluting

Question 20

Contact lenses vs spectacles

-accommodation of hyperopes vs myopes

Answer 20

H accomm less with CLS

M accomm MORE with CLS

Question 21

Contact lenses vs spectacles

-magnification of hyperopes vs myopes

Answer 21

H have smaller mag with CLS

M have MORE mag with CLS

Question 22

Contact lenses vs spectacles

-convergence of hyperopes vs myopes

Answer 22

H converge less with CLS

M converge MORE with CLS