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Possible Problems with High Index Lenses
Guillaume wrote:
I recently bought a high quality plastic frame outfitted with Carl Zeiss 1.67 high index lenses w/Carat Advantage coating. My prescription is -3.25 LE and -2.75 RE with no astigmatism/other problems. Looking straight without moving is great but the image gets distorted if I move my head up/down and left/right (aberrations?). When I move my head up/down the image gets ''compressed'' and when I move left/right it ''tips'' or gets bent. It's a bit hard to explain I guess. I will consult the seller but I'd like to get your opinion or what could cause these visual disturbances (wrong PD? Lenses too tight in frame? etc.) Thank you very much for your help, Guillaume.
Dr Langis Michaud's response:
Dear Guillaume
The first thing to consider is the high index of the glasses you got. Usually, this type of material is selected when the prescription is very high and we need to make the lenses thinner. This is not the case with your refractive error. Perhaps the frame you have selected dictated that need but I cannot really explain why it was provided to you. High index lenses are made thinner but they also compromise some elements of their optical function. For example, the movement and distortion you feel are directly linked with the behaviour of this material, outside of the optical center. If your frame is quite large, this is worst. You are right to say also that some mis-manufacturing process can occur: a tight lens will create distortion and will lead to the symptoms that you have. It would be surprising however that this affects both lenses at the same time.
My recommendation: go back to your provider and ask to redo the job with a regular index – if this is not possible due to frame constraints, select another frame- the person who guided you did not do a good job if the frame was selected too wide for your needs.
Good luck
Dr Langis Michaud, OD, MSc, FAAO (Dipl)
Associate Professor – U de M
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