Aspheric & Atoric Lenses

conic

aspheric surfaces are based on a surface curvature that comes from a _______ section

1. improved optics

2. flatter base curve

3. thinner lens

4. assures the lens has a good, tight fit in the frame

5. allows PAL to produce variable add power

what are the purposes for aspheric designs?

+7, -22 to -25

for powers greater than ____ in the plus direction & greater than ____ in the minus direction, there is no spherically-based that can correct for oblique astigmatism

aspherics de-couple base curve from lens power

why can aspherics have flatter lens base curves?

center

an aspheric plus lens has a thinner ____ thickness

edge

an aspheric minus lens has a thinner ____ thickness

6D

most frames are made to hold a lens best that has a _____ base curve

BC to be flattened & reduces lens center thickness

using plus-powered aspherics will allow for what 2 things? (improves cosmetic appearance)

reduces edge thickness

for a minus lens, what is the benefit of backside asphericity?

steeper

using ordinary manufacturing methods, the __________ the base curve, the harder it is to keep the lens in the frame

aspheric

is a PAL spheric or aspheric?

reduce

an aspheric design can often ____ distortion

peripheral magnification

with an aspheric design, plus lens wearers are able to view the world w/o as much __________ as with a spheric

minification

with an aspheric design, minus lens wearers are able to view the world w/o as much ______ as with a spheric

they were used to the distortion with their regular spheric glasses

why do some people complain about distortion w/ their new aspherics?

1. moving a lens clock sideways

2. viewing a grid pattern

3. noticing flatness of the front & back curve compared to other lenses of equal powers

4. hidden markings from some manufacturers

what are some ways to identify an aspheric lens?

1. OC should always be in the middle of the central, spheric portion of the lens

2. drop the MRP height from the pupil center using the 1 for 2 rule but don’t drop more than 5mm below

3. use monocular PDs

4. minimize vertex distance

what must be kept in mind when fitting aspherics?

must grind in the prism

for aspherics, any prescribed prism must be __________ so that the MRP remains in the center of the aspheric zone

middle, central spheric portion of the lens

where should the OC be always for an aspheric lens?

1, 2

the MRP should be dropped from the pupil center ____mm for every ____deg of pantoscopic tilt

5

don’t drop the MRP more than _____mm below the pupil center

Eyezen start lenses

single vision lens designed w/ different amounts of asphericity in the distance & near portions of the lens because base curve is dependent upon object distance as well as lens power

decreases

optical performance _______ as lens form departs from the ideal base curve

decreases

optical performance _______ w/ increasing cylinder power

spherical

for simple sphere lenses, the front & back surfaces are ______

spherical, toric

for spherocylinder lenses, the front surface is _____ and the back surface is ________

aspheric, spherical

for simple sphere aspheric lenses, the front surface is _____ and the back surface is _______

aspheric, toric

for spherocylinder aspheric lenses, the front surface is ______ and the back surface is ______

one

spheric & aspheric lens designs can only correct aberrations in ____ of the major meridians

both

atoric lens designs can correct aberrations in _____ meridians at once

spheric, atoric

the most common atoric lens style is a lens made with a _____ front surface & an _____ back surface

double aspheric

term sometimes used to describe a lens where the front surface is aspheric & the back surface is atoric

atoric

what lens design allows for lens aberrations to be overcome in both meridians?

+3.00D

for plus, an aspheric may easily be recommended when the power goes above ______

lower

the larger the frame, the ______ the plus power for recommending an aspheric

-3.00D

for minus, an aspheric may be recommended for powers above _____

2.00D

when anisometropia exceeds _____, consider aspheric/atorics

1. for children who are sensitive about how their glasses look

2. for CL wearers so they won’t over-wear to avoid what would otherwise be thick, ugly glasses

3. for older individuals to decrease lens weight

what are some cosmetic/comfort factors to consider using aspherics?

1. in situations where aspherics would have been used but especially in the presence of high cyl power

2. in cyl power greater than 2.00D (even lower cyl powers)

when should atorics be recommended?

2.00D

atorics are appropriate any time cyl power is greater than _____

BO, BI

wrapped frames induce _____ prism, so ____ is added to compensate

full aspheric design

aspheric design that begins its asphericity at the very center of the lens

non-full aspheric design

aspheric design: central cap w/ spherical optics & begins its aspheriticy at the point where the cap ends

they create oblique astigmatism & induce prism

what is the problem with wrap frames?

1. angle of tilt

2. steepness of BC

3. index of material

4. thickness of lens

prismatic effect induced by wrap glasses depends on what factors?

unwanted prism will be present in the lenses but will not be detected through the lensometer

for wrapped frames, unless the glasses are compensated through digital surfacing, what occurs?

the amount of prism manifested in the glasses will not match the prescription

for wrapped frames with prescribed prism, unless the glasses are compensated through digital surfacing, what will occur?

spheric

the degree of curvature of a _______ lens is continuously uniform with a consistent radius of curvature through its entire surface

T

T/F: you would use an aspheric design to get a good, tight fit into the frame

+7, -23

once lens powers go beyond the _____ to the ____D range, it is necessary to use an aspheric design in order to obtain good peripheral optics

T

T/F: flattening a regular spherically-based lens will result in unwanted cylinder because of oblique astigmatism

F

T/F: most frames are made to hold a lens w/ a 5.00D BC

T

T/F: PAL achieve their add power gain from a progressively steepening surface curvature, thus they are aspheric

2.00, 1.25

atoric lenses should be considered for recommendation for all cylinder powers over _____D but may be advantageous for anyone with a cyl power over _____D

F

T/F: prescribed decentered prism can be used in an aspheric lens because the asphericity will not be misplaced relative to the eye

markings

you may be able to look for identifying _________ to help identify if a lens is aspheric/atoric & not spherical

-3.00, +3.00, greater than 2.00D

what are the guideline prescription powers that may be uesd when recommending aspheric lenses? minus, plus, aniso difference

T

T/F: aspheric lens designs can be recommended for older wearers to help decrease the lens weight

T

T/F: those being changed from conventional spherically based lenses into aspheric or atoric lenses should be warned about the adaptation time that will be necessary

T

T/F: a lenticular lens has a central area called the aperture where the prescribed lens power is located

T

T/F: an advantage of a lenticular design is its lens thickness reduction

multidrop

a _______ lens can incorporate the advantages of optically sound aspherics for near-peripheral viewing, plus a fast-changing aspheric drop toward the edge resulting in what could almost be considered a blended aspheric lenticular

decrease

for myodisc lenses of the same sized bowl diameter, a decrease in power will mean a ___________ (increase/decrease) in carrier thickness

spheric plus lenticular

myodisc

minus lenticular

Welsh 4-drop