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Ophthalmology & Optometry/Chromatic aberration in perypheral region of eyeglasses: how to improve?

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Hi,

My question is pretty specific.

I wear eyeglasses to correct +5D hyperopia and 0.75/110 astigmatism (this is the worst eye, the other one has a slightly different prescription).

I'm experiencing a high level of blurriness and color fringes when looking off-center (even slightly), while my vision is perfectly clear when looking straight at the center. After googling around a little bit, I'm pretty sure what I'm observing is CHROMATIC ABERRATION and it seems to turn down to the low Abbe number of my lenses.

My lenses are of high-index (1.67) plastic, which are the thinnest ones but have the lowest Abbe number which is around 30 or 32.


I know there are other materials with higher Abbe number at the expense of being thicker and/or heavier.

The question is: HOW MUCH higher should the Abbe number be to provide a NOTICEABLE IMPROVEMENT? I know, the higher the better, but that also mean much thicker lenses (CR39) and/or heavier (crown glass) so I have to look for a viable trade-off, and also need to know whether or not there is any possibility at all to achieve a significant improvement.


There seem to exist affordable glass options (affordable in terms of thickness/weight) with Abbe numbers of around 42 or 47.
Will 42 give me a noticeable improvement over my current lenses that have a value of 30? What about 47?

The best options at all seem to be either CR39 and crown glass, but these would probably be too thick (CR39) and heavy (glass). These have an Abbe number of 58: is this a significant improvement over 30?

Let's assume that my initial premise is correct (i.e. the problem being chromatic aberration in the first place, of which I'm pretty sure).

The question is (1) whether or not it can be solved at all (i.e., are the differences noticeable at all, even with the "best" materials), and (2) if so, whether a half-way solution will be enough (there are kinds of glass that have about 47 Abbe number with around 1.6 index, so they would be a thicker and heavier but I can definitely stand that if it's worth)

Or, of course, (3) whether there exists a miracle solutions such a super-thin super-light material with a super-high Abbe number and practically no chromatic aberration, but I guess I can discard this one :)

Thanks in advance
Teo

P.S. I've been farsighted and wearing glasses since I was a child, but the prescription used to be hypocorrected when I was younger and have been augmented with time, so my prescription now is higher than it used to be, and I didn't notice this very problem until recent years, which I guess is due to the higher prescription _and_ higher refraction indices.

Answer
Dear Teo,

High refractive index lenses generally have low abbe value that sometime causes lateral chromatic aberration.

These aberrations can be minimized to a great extent by using following techniques.
#1. Select a well centered spectacle frame. Your eye should be in the center of the rim and frame shouldnt be too big.
#2. Use double aspheric 1.6 or 1.67 index lens with Anti Reflection Coating
#3  Double aspheric lenses can be made on a flatter base curve, which further minimizes the aberration.

Regards
Optom.Amit Sharma

Ophthalmology & Optometry

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Optom. Amit Sharma

Expertise

Happy to answer any question related to the field of Optometry and opticals. Specialize in Corneal, corneal-limbal and Scleral RGP (Rigid Gas Permeable ) contact lenses for keratoconus, post lasik ectasia , dry eyes, etc,

Experience

I have been in the field of Optometry since 1989 . Worked as an Optometrist at Shroff Eye Centre New Delhi (INDIA) for 4 years. Established my own Optometry clinic In 1997 and have been practicing since then.

Organizations
OPTOMETRY CLINIC FOR SCLERAL AND CORNEAL RGP LENSES, SPECTIQUE INDIA, (www.spectiqueindia.net)

Education/Credentials
M.Optom D.Opt.(AIIMS)

Awards and Honors
Optometrist of the year 2009 Award by Cooper Vision.

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