Aspheric lenses

discussion about Aspheric lens, fitting, indication,advantage and Disadvantages with traditional aspheric lens,need of Asphericity,Aspheric Lens Design, identification, troubleshooting

1. Aspheric Lenses
-ANURAG SHUKLA
FELLOW OPTOM.
SHROFF CHARITY EYE HOSPITAL ,DELHI

2. What we expect from spectacle
lens?
Good Optics
Cosmesis-Natural Appearance
Light in weight
Thin
Natural vision

3. Disadvantages with traditional
lens designs
Lens become thicker when improving
optics
Optics hampered when reducing thickness
Wearers eyes appear bulgy in high plus
powers
Difficult to fit into frames

4. Why do we need Asphericity?
Offers slimmer profile
Superior Optics
Natural Appearance
Lighter weight

5. Whom should I suggest?
Prescriptions more than +/-3.00 DS
(Need your input)
Unsatisfied spectacle wearer
Person requiring good peripheral vision
Person expecting natural appearance with
their spectacles.
Persons who like to use high end products

6. Video -Spherical Vs. Aspherical

7. Something which we must
know
Spectacle lenses inherently produce following
aberrations which can be taken care by applying
asphericity
◦Oblique astigmatism(only with aspherics)
◦Spherical Aberration (with aspherics as well as
hi index)
◦Distortion (with aspherics as well as hi index)

8. Oblique Astigmatism
Lens faces oblique astigmatism when
viewing obliquely through lens

9. Distortion

10. Aspheric Lens Design
Change in radius of curvature from center to
periphery
Symmetric axially or rotationally
Atoric surface -Different asphericity applied in
two different meridians

11. Various options available
Materials available: Cr39, Trivex,
Polyurethane
Index available: 1.498, 1.53, 1.67, 1.74
Available in: Single vision and
Progressives, not very common in bifocals
Tints: Available in clear and photo
chromatic tints
For available power range: Need to refer
to individual company catalogue

12. Challenges for us
How to recommend?
How do we fit?
How do we identify aspheric?

13. How to recommend?
Identify the consumers for whom it will be
really beneficial

14. Before suggesting a product
Check
◦Patients expectations
◦Type of lens he is already wearing
◦Base curve of the previous lens
◦Previous lens power
◦Is there a change in the prescription?
◦Availability as per prescription

15. Be Prepared for these FAQ’s?
How much thinner it will be?
How much lighter it will be?
Does it come in all lens materials?
Is it available in bifocals?
Do I need to select any special frame?

16. How to fit Aspheric
Pentascopic tilt
Monoc
ular
PD
Monoc
ular
PD
3229
61
Take monocular PD’s
Rule of thumb for pantoscopic tilt
Lower Optical Centre by 1 mm
for 2 degrees of pantoscopic tilt
Avoid decentration, if prescribed,
prisms should be ground in

17. Importance of accurate fitting
Optical axis should pass through the
center of rotation
Increased off axis errors due to tilt or de-
centration
Errors due to improper fitting will be
larger, may be twice as compared to
spherical surfaces

18. Counseling is important
Adaptation: especially for hi-power
Change in magnification properties
Amount and location of reflected images
(for higher Rx ARC is preferred).

19. Difficulties
Difficult to assess optical performance
Lens gauge can not measure amount of
asphericity
Difficult to assess parameters of previous
lens
Back surface may touch eyelids

20. Identification
Geneva Lens Measure

21. Identification
Lensometer

22. Identification

23. Troubleshooting
Listen to the patient’s complaints carefully
Check the following parameters of
spectacles
◦Lens power
◦PD and Optical Centration Distance
◦Pantoscopic tilt
◦Base curve

24. Troubleshooting
Check the following on patient
◦Check Monocular PD
◦Adjust the pantoscopic tilt, if not proper
◦Adjust the nose pads and reduce the vertex
distance
◦Counsel the wearer for adaptation
Still the problem persist recheck the
refraction.

25. THANK YOU