[Leica] Chromatic aberration/fringing in spectacles?

[rclompus at mac.com (Richard Clompus)]

Peter,

Perhaps I can help with this topic - as an optometrist.  I was in  
private practice in Pennsylvania for 20 years, worked in Roanoke, VA  
with a start up J&J company that developed a new technology  
progressive spectacle lens (DEFINITY) and currently work with another  
J&J company producing ACUVUE contact lenses.

Most spectacle lenses are made from a resin called CR-39 from the  
1960's.  It has a relatively low index of refraction (1.50).  Optics  
are good, aberrations are low but the lens can be thick for higher  
prescriptions (+/- 4.00 diopters).  They do not block UV light.

Polycarbonate lenses are considered mid-index lenses (1.55) and have  
excellent break resistant qualities and naturally block UV.   
Unfortunately, they also have a high Abbe number resulting in off-axis  
chromatic aberration (color fringing) when looking obliquely through  
the lens - when looking to the side.

High index lenses (index > 1.60) are thinner with higher prescriptions  
but also suffer from chromatic aberrations.

Polycarbonate lenses in the early 1990's developed a bad reputation  
for patients when docs and opticians were not as familiar with them.   
Today, much of the chromatic aberration (color fringing) can be  
significantly decreased with a multi-layer (AR) antireflective coating  
- just like that applied to camera lenses.  Less reflections, less  
apparent fringing.  In most cases, the patient will adjust over a 14  
day period where the fringing may still be present but not consciously  
apparent to the viewer.  The brain is a wonderful optical processor  
that adjusts what we "see" in real time.  Spectacle lenses cannot be  
returned to the lab to be AR coated (antireflective coated) after they  
are dispensed.  Micro scratches would prevent the multi-thin layers of  
vacuum deposited material to adhere to the lens.

In general, when a patient does not adapt to a lens, they should go  
back to their doctor or optician who supplied it to ask for a change.   
In this case, it could be to remake the prescription in a different  
material.  My office policy was to remake them at no additional  
charge.  Every office is different but you grow your practice by  
creating happy patients.  Don't give up too soon on polycarbonate.  I  
have worn it for years with the color fringing resolved.  AR coating  
helps.  Sometimes scotch straight up works for the first few days  
until adaptation kicks in.  Balvenie works best for me.

If I can be of any further help, please feel free to contact me.

Best regards,

Richard Clompus, OD
rclompus@mac.com
Ponte Vedra Beach, FL