Soft toric lens design clinical perspective

Question 1

incidence of astig. in general pop.

Answer 1

0. 75 = 45%
1. 00 = 34%
2. 50 = 20%
3. 00 = 10%

Question 2

spheroequivalent complacency

Answer 2

use toric when refractive cyl is 0.75 or greaater

use torics when BVA with spherical hydrogels is one or more lines less than best spec acuity

Question 3

toric cl lens principles

Answer 3

lens conform to shape of cornea

correcting cyl provide proper in vivo meridonial powers

lens should remain in correct orientation and relocate rapidly

Question 4

toric lens fitting criteria

Answer 4

criteria

• full corneal centration and coverage
• lens edge and conforms to eye shape
• movement in primary and upward gaze, approx 0.5mm
• keratometric mires => clear stable
• comfort => good
• VA => good, stable
• rotation and stablity => stable rotation with consistent return after off axis rotation

Question 5

spherical vs. toric proper fits

Answer 5

spherical:

• proper movement
• proper centration

toric:

• proper movement
• proper centration
• base mark stability

Question 6

fitting from dx lens

Answer 6

• base mark position
• lens comfort
• equilibration
• proper drift axis

Question 7

prism base

Answer 7

prism base marks axial realignment

3 base marks, 30 degrees apart
-center is primary

Question 8

fitting toric lens

Answer 8

select closest to pt’s rx

• cyl within 10 deg
• sphere within 1D

allow lens to equilibrate for 2-3 min

Question 9

fitting procedure

Answer 9

1. meet basic criteria?
   - good centration
   - adequate mvmt
   - corneal coverage
   - stability on eye in lateral and upgaze
   - rotational stability of base mark
2. over-refraction
   - perform spherical over-refraction and measure VA
   - determine final lens spherical power
3. compensate for axial realingment
   - locate toric base mark
   - estimate rotational displacement from center line
   - compensate axis of spec rx to determine correct toric soft lens axis

Question 10

lars formula

Answer 10

LARS
left
add
right
subtract

CW
add
CCW
sub

Question 11

axis compensation

Answer 11

optical principle that ensures toric lens, in natural position, keeps CL toric axis aligned with patient’s spec axis

cyl axis only correct if lens continue to orieent at position compensated for

do not expect compensated toric lens will have base mark appear at 6 oclock = NOT COMPENSATION

Question 12

use clockwork

Answer 12

each hour = 30 degrees

Question 13

refractive considerations

Answer 13

spherical overrefraction

spherocylindrical overrefraction

dec. cyl to dec. variable vision

importance of refractive components:

• axis
• cyl power
• sphere power

vertex must be calculated for each power meridian

Question 14

undercorrect cyl power why?

Answer 14

undercorrecting cyl is often needed simply due to vertex consideration

vertex applies to RX > 4D

additional slight undercorrection in cyl also beneficial => less distortion if lens rotate away

Question 15

toric lens observation

Answer 15

full corneal coverage, with 0.25 - 0.5 mm movement

• good fit: quick return to axis
• tight fit: slow return to axis

loose fit: lens orientation unstable and inconsistent

Question 16

tight fit toric

Answer 16

show large degrees of angular mislocation > 20 degrees

little to no movement with blink

dont bother compensating for rotation if drift angles large

Question 17

diagnostic lens method toric fitting

Answer 17

advantages:
immediately observe lens behavior
-result in BVA in difficult-to-fit pt

Question 18

problem solving toric lens

Answer 18

fitting consideration

refractive considerations

Question 19

when lens moved out of position, does it return to original position?

Answer 19

1) check base mark position

2) if not where anticipated => rotate to proper position

Question 20

refractive considerations (SCO) spherocylindrical overrefraction

Answer 20

reduced VA response

accurate SCO improve VA means CL power is off, spec rx is off, lens rotate

SCO does not improve VA means fit of lens is poor, quality of lens is poor, must rule out pathology

overrefraction results

OR axis = refraction axis -> inc. lens cyl power

OR axis = 90 deg away -> dec. lens cyl power

OR sph/cyl at oblique -> adjust axis

OR cyl = lens cyl power -> lens 30 deg off

OR cyl = 1/3 lens cyl power -> lens is 10 deg off

Question 21

checking lens optics

Answer 21

if reflex bad:
optics bad, defective lens -> reorder

if reflex good:
blur cause unknown -> check refraction, tear quality, new lens

Question 22

why do toric hydrogels mislocate

Answer 22

natural vector forces of the lids

lens fit too tightly or too loosely

effects of nonuniform meridonal edge thickness

excessive inferior edge thickness

effects of tight lids/narrow palpebral apertures

Question 23

prism ballast

Answer 23

increases likelyhood of rotation
-balanced by bottom weighting

-blink stabilized design: balanced with four zones of stability

Question 24

rotation dependent

Answer 24

on differences in meridional edge thickness -> rotats to thicker meridian

Question 25

stabilization methods and design

Answer 25

prism ballast truncation with prism ballast thin zone slab-off periballast and eccentric lenticulation combination

Question 26

prism ballast

Answer 26

method of stabilixation -addition of 0.75 - 2.0 D base down prism reducing rotation -require inferior chamfering or slab-off for good comfort

Question 27

chamfer or lenticulation

Answer 27

provides nearly equal thicness around lens periphery - reduces torsional effects from differntial lens thickness provides better comfort minimizes lens compression at periphery

Question 28

disadvantages of prism-ballas

Answer 28

thickness variation lens mass localized pressure on cornea @prism base resulting: inc. centra, temporal, and inferior corneal thickness

Question 29

eccentric lenticulation

Answer 29

material removed from anterior lenticular surface upper and lower thin zones equal thickness edge thickness uniform thorughout lens circumference high cyl and oblique axes

Question 30

combination stabilization

Answer 30

incorporates eccentric lenticulation, thin zones, and back surface toricity edge thicness uniform throughout lens circumference no prism in optic zone minimal rotation allows empirical fitting

Question 31

modern stabilization method

Answer 31

blink stabilized - balanced with four zone of stability - more gaze independence - accelerated slopes: more lid power - symmetrical weighting : limit gravity - thin lens

Question 32

toric brands

Answer 32

cooper: biofinity toric, avaira toric, and proclear toric J&J: acuvue oasys for astig B+L: purevision toric alcon: air optix for astigmatism

Question 33

acuvue oasys for astig

Answer 33

silicone hydrogel 2 week replaceent scribe marks vertical comes in 0.75, 1.25, 1.75, 2.25, 2,75 cyl powers

Question 34

pure vision toric

Answer 34

anterior aspheric optics to reduce inherent and induced spherical aberration prism ballasting geometry with 360 comfort chamfer for enhanced rotational stability across all powers balanced vertical thickness profile for excellent axis stabilization and exceptional vision

Question 35

air optix for astig

Answer 35

powers: +6 to -6 in 0.25 step - 6.50 to -10 in 0.5 steps cyl: 0.75,1.25,1.75,2.25 axe: 10 deg steps material lotrafilcon B bc 87 dia: 14.5 water content 33% DK, Dk/t: 110, 108 @ -3.00 surface: permanet plasma treatment back surface: toric

Question 36

proclear XR | preference XR

Answer 36

extended range torics offered by cooper vision cost higher 4 pack options

Question 37

improvement in hypoxia related signs of corneal health

Answer 37

silicone hydrogel toric lens offer high oxygen transmissibility to help protect patients from signs and symptoms of corneal oxygen deficiency for whiter healthy-looking eyes

Question 38

customized lens

Answer 38

specialeyes corp will make custom spherical or custom toric great for oblique axes or high powers not avaialble

Question 39

daily disposable torics

Answer 39

clearsight 1day aqua comfort plus toric dailies 1 day acuvue moist for astigmatism B+L purevision daily disposable for astigmatism

Question 40

proclear multifocal toric

Answer 40

bc 8.3 to 8.0 spher pwoer -20 to +20 cyl -0.75 to -2.75 add powrs: +1.00 to +3.5

Question 41

custoom toric multifocals

Answer 41

intelliwave multifocal and multifocal toric - supply keratometr readings - spec refraction including spher, cyl, axis and add HVID dominant eye; pupil diameter in normal light Sihy-any rx