7 - Contacts2 Flashcards Preview

KMK - Physiological Optics > 7 - Contacts2 > Flashcards

Flashcards in 7 - Contacts2 Deck (22)
Loading flashcards...
1

Aspheric design

Flattens toward the periphery - mimics cornea

Better centration and comfort
Decr magnitude of spherical aberrations

Primary disadvantage = decr tear exchange

2

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

3

Super basic difference bw flexure and warpage

F = on eye only

W = on or off eye

4

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

5

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

Hyperopes/plus GPs

Myopes/minus GPs with center thickness >0.13mm

6

Flexure
-how you find/measure

Keratometry
-if read toric = flexure

7

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

8

Warpage
-main cause
-effects

Excessive digital cleaning

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

9

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

10

Calculating total amount of gas that actually passes thru a lens

Transmissivity = Dk/t

Where t is thickness of lens in cm

11

Soft lenses
-which surface is usually toric

Front

12

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

13

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

14

Soft lenses
-how to pick diameter of lens

HVID + 3mm

Ensures 1.5mm extension beyond limbus for 360 degrees

15

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

16

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

17

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

Incr stiffness with:
-incr modulus
-incr thickness
-decr water

18

Soft lenses
-benefits of high-modulus sihy lenses (3)

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

19

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

20

Contact lenses vs spectacles
-accommodation of hyperopes vs myopes

H accomm less with CLS

M accomm MORE with CLS

21

Contact lenses vs spectacles
-magnification of hyperopes vs myopes

H have smaller mag with CLS

M have MORE mag with CLS

22

Contact lenses vs spectacles
-convergence of hyperopes vs myopes

H converge less with CLS

M converge MORE with CLS