Soft toric lens design clinical perspective Flashcards
incidence of astig. in general pop.
- 75 = 45%
- 00 = 34%
- 50 = 20%
- 00 = 10%
spheroequivalent complacency
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
toric cl lens principles
lens conform to shape of cornea
correcting cyl provide proper in vivo meridonial powers
lens should remain in correct orientation and relocate rapidly
toric lens fitting criteria
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
spherical vs. toric proper fits
spherical:
- proper movement
- proper centration
toric:
- proper movement
- proper centration
- base mark stability
fitting from dx lens
- base mark position
- lens comfort
- equilibration
- proper drift axis
prism base
prism base marks axial realignment
3 base marks, 30 degrees apart
-center is primary
fitting toric lens
select closest to pt’s rx
- cyl within 10 deg
- sphere within 1D
allow lens to equilibrate for 2-3 min
fitting procedure
- meet basic criteria?
- good centration
- adequate mvmt
- corneal coverage
- stability on eye in lateral and upgaze
- rotational stability of base mark - over-refraction
- perform spherical over-refraction and measure VA
- determine final lens spherical power - 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
lars formula
LARS left add right subtract
CW
add
CCW
sub
axis compensation
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
use clockwork
each hour = 30 degrees
refractive considerations
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
undercorrect cyl power why?
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
toric lens observation
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
tight fit toric
show large degrees of angular mislocation > 20 degrees
little to no movement with blink
dont bother compensating for rotation if drift angles large
diagnostic lens method toric fitting
advantages:
immediately observe lens behavior
-result in BVA in difficult-to-fit pt
problem solving toric lens
fitting consideration
refractive considerations
when lens moved out of position, does it return to original position?
1) check base mark position
2) if not where anticipated => rotate to proper position
refractive considerations (SCO) spherocylindrical overrefraction
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
checking lens optics
if reflex bad:
optics bad, defective lens -> reorder
if reflex good:
blur cause unknown -> check refraction, tear quality, new lens
why do toric hydrogels mislocate
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
prism ballast
increases likelyhood of rotation
-balanced by bottom weighting
-blink stabilized design: balanced with four zones of stability
rotation dependent
on differences in meridional edge thickness -> rotats to thicker meridian
stabilization methods and design
prism ballast
truncation with prism ballast
thin zone slab-off
periballast and eccentric lenticulation
combination
prism ballast
method of stabilixation
-addition of 0.75 - 2.0 D base down prism reducing rotation
-require inferior chamfering or slab-off for good comfort
chamfer or lenticulation
provides nearly equal thicness around lens periphery - reduces torsional effects from differntial lens thickness
provides better comfort
minimizes lens compression at periphery
disadvantages of prism-ballas
thickness variation
lens mass
localized pressure on cornea @prism base
resulting: inc. centra, temporal, and inferior corneal thickness
eccentric lenticulation
material removed from anterior lenticular surface
upper and lower thin zones equal thickness
edge thickness uniform thorughout lens circumference
high cyl and oblique axes
combination stabilization
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
modern stabilization method
blink stabilized
- balanced with four zone of stability
- more gaze independence
- accelerated slopes: more lid power
- symmetrical weighting : limit gravity
- thin lens
toric brands
cooper: biofinity toric, avaira toric, and proclear toric
J&J: acuvue oasys for astig
B+L: purevision toric
alcon: air optix for astigmatism
acuvue oasys for astig
silicone hydrogel
2 week replaceent
scribe marks vertical
comes in 0.75, 1.25, 1.75, 2.25, 2,75 cyl powers
pure vision toric
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
air optix for astig
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
proclear XR
preference XR
extended range torics offered by cooper vision
cost higher
4 pack options
improvement in hypoxia related signs of corneal health
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
customized lens
specialeyes corp will make custom spherical or custom toric
great for oblique axes or high powers not avaialble
daily disposable torics
clearsight 1day
aqua comfort plus toric dailies
1 day acuvue moist for astigmatism
B+L purevision daily disposable for astigmatism
proclear multifocal toric
bc 8.3 to 8.0
spher pwoer -20 to +20
cyl -0.75 to -2.75
add powrs: +1.00 to +3.5
custoom toric multifocals
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
