Aspheric

Question 1

WHY ASPHERICS?

Answer 1

• Reduce aberrations
• Reduce magnification (flatter lens)
• Reduce thickness/weight
• Improve lens fit into frame (especially for plus lens)
• Progressive lenses are aspherics

Question 2

Current aspherics

Answer 2

• Lens power, lens thickness, panto tilt, face form angle (dihedral angle), vertex distance
• Higher order polynomial: correcting beyond 2nd order
• “polynomial” aspheric lenses

Question 3

aspheric surface

Answer 3

• creates a flatter lens (plus power: thinner centers; minus lens: thinner edges)
• flattening a lens results in power errors and astigmatic errors
• use of an aspheric surface results in negating or reducing the power and astigmatic errors
• deviates from conventional spherical best form
• front vs. back aspheric

Question 4

aspheric lenses

Answer 4

• plus lens–to reduce the power error and astigmatic error, the lens front surface is made aspheric with
  the lens flattening as one moves from the lens center towards the edge;
• minus lenses–front surface made aspheric withlens steepening towards edge
• more base curves, each covering a smaller range
• asphericity increases as flattening increases

Question 5

too much asphericity:

Answer 5

a great looking lens but potentially poorer optics if increasing asphericity
is not resolving peripheral aberrations

Question 6

ATORIC LENSES

Answer 6

• extension of aspheric concept to toric surfaces
• greater cylinder powers, errors along each meridian are different (i.e. aberrations)
• need to reduce errors optimally utilizing aspheric concept along each meridian (or at least one of the
  meridian is aspheric)
• consequence: aspheric + toric = atoric lens design

Question 7

Type I Atoric

Answer 7

atoric on cylinder side & spherical on
opposite side
-asphericity varies from one principal meridian to the other

Question 8

Type II Atoric

Answer 8

atoric surface with no true cylindrical
correction at vertex & circular toric surface on opposite side

Question 9

Type III Atoric

Answer 9

freeform atoric surfaces, used on complex or progressive type of lenses
-PAL front, complex atoric back

Question 10

vision through circular torics vs atoric

Answer 10

atoric has obvious improvement in the flear FoV

Question 11

ATORIC LENSES traits

Answer 11

• concept utilized with single vision and progressive lens designs
• visual field maximization
• not material dependent
• thinner lens
• less magnification
• better aberration reduction

Question 12

atoric utilization

Answer 12

• high cylinder prescriptions
• anisometropia
• anisekonic lenses
• general reduction in lens thickness, lens volume, lens weight

Question 13

Myopia Control Lenses

Answer 13

*Area of defocusing segments/lenslet (aka treatment zone): honeycomb appearance with each lenslet having a
+3.50D power interspersed with clear zones
* D.O.T (Diffusion optics technology)
* reduces myopia progression in
children by incorporating thousands
of micro-dots into lenses, which
scatter light and reduce contrast on
the retina

Question 14

ASPHERIC LENS FITTING

Answer 14

• Rx consideration: >+2.00; >-3.00
• Lens index: 1.67, 1.701, 1.74; (typically aspheric)
• Lens index: 1.60, 1.586, 1.53 (Trivex), 1.498 (aspheric &
  spheric)
• Full aspheric vs “not so full” aspheric
• monocular PD’s (pupillometer)
• vertical OC placement
• OC height
• 1 mm drop per 2 degrees of tilt
• Alternative option: patient tilts chin up with frame on
  until plane of frame perpendicular to floor, mark lens
  with patient in primary gaze
• no decentration (prism)
• vertex distance consideration (FOV)
• no greater than 12-13mm