Aspheric Lenses Flashcards
2 advantages of aspheric lenses:
reduce off axis aberrations
reduce lens thickness
asphericity of Q=0 means:
it’s a circle
Q>0 is a _ ellipse, and _ curved
oblate, more
-1
prolate, less
if a plane cuts through a cone that is parallel to the side of the cone, a _ is created
asphericity Q= _
parabola
-1 (always flatter than circle and ellipse
incident rays parallel to the axis reflect off a paraboloid, and always pass through the focal point; therefore there are no _ aberrations
spherical
if a plane intersects the cone and its base, the curve is a _
Q=_
hyperbola
from flattest to steepest:
hyperbola, parabola, prolate ellipse, circle, oblate ellipse
as Q becomes more negative, sagittal depth _
decreases
power at the tangential meridian of an ellipsoid is the _
power at the sagittal meridian is the _
minimum
increasing.. max, idk? (smaller radius of curvature)
vertex power is _, (greater than tangential and sagittal)
maximum
power drops off faster along the _ meridian
tangential
with full aspheric lenses, the aspericity starts _ at the vertex
immediately
nonfull aspheric lenses have _
central area that is spherical is called: _
outer part of the lens is usually aspheric for _
a spherical component and an aspherical component
cap
progressive add power
aspheric lenses are flatter than spherical, so their sagittal depths are _
smaller
high +: a lens with an aspheric base curve will flatten the front lens which:
- betters the cosmetics
- decreases RA and curvature of field
- reduces _
thickness
plus lenses: periphery of front and back surfaces are _ ,center remains spherical
flattened (entire lens thinner)
minus lenses: peripheral portion of front is _
peripheral portion of back is _
steepened
flattened
(center is not changed)
an aspheric lens will produce _, and is used for _
progressive power changes
PALs (distance portion is spherical)
aspherical lenses are best used for _ rxs
_ lenses are best used if astigmatism is present
spherical
atoric
atoric lenses have _ surface powers
2 aspheric
like aspheric lenses, atoric lenses will
_ peripheral aberrations
reduce
atoric lenses are recommended for >_D of astigmatism
2.00
atoric lenses are never used for _ rxs
spherical
finished single vision atoric lens has
_ front surface
_ back surface
spherical
atroic
semi finished single vision lens has
_ front surface
_ back surface
atoric
spherocylindrical
can decentration be used in an aspheric lens?
how is prism achieved?
NO (pt must look through optical center)
must be grounded into lens (only way)
to identify aspheric lens:
- move clock along _ meridian, if power changes it is aspheric
- use _ pattern to see if peripheral aberrations are min
- look at front and back surfaces compared to spherical lenses of similar rxs (experience)
- _ marking
tangential
grid
manufacturer
when dispensing aspheric lenses: DRP must coincide with _
OC
lenses with aspheric peripheries can be decentered 1mm for every 2 degrees of pantoscopic tilt.. but no more than _ degrees of tilt is allowed
10
when to dispense aspheric lenses:
- _plus or minus
- _ patients
- people who want _
- _ wearers to reduce weight
high
anisometropic
good cosmetics
old
