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Medical Forum / General / Vision / December 2005bifocal line distortion
I just got a new pair of polycarbonate flat top 35 bifocals and find that there is some blur around the segment line that is very distracting and cuts into the field of vision. I've also noticed some "rainbow" effects from the line in certain light. My old bifocal glasses with the same prescription and plastic lenses had none of these problems; the jump was sharp and relatively unobtrusive. Would the polycarbonate material most likely be causing these problems? Or poor quality work? I'm not sure right now if I should have them remade by the same lab in plastic, and hope for the best, or return them and get the lenses made by the lab that did my old glasses. Cal It could be defective lenses/poor quality work, or it could be just the polycarb, which are known for their chromatic aberrations (so if the "blur" has some color fringes, especially yellow, it's the polycarb). If standard plastic is an option (not drilled lenses), I'd go that way, unless you had a real good reason to chose polycarb... w.stacy, o.d. >I just got a new pair of polycarbonate flat top 35 bifocals and find >that there is some blur around the segment line that is very [quoted text clipped - 10 lines] > > >It could be defective lenses/poor quality work, or it could be just the >polycarb, which are known for their chromatic aberrations (so if the [quoted text clipped - 7 lines] >>that there is some blur around the segment line that is very >>distracting and cuts into the field of vision. Cal, Another possibility is a coating overrun on the seg or bifocal line. This is essentially a quality control problem and can usually be corrected by re-making the lens. Consider using Trivex ("in mold" scratch coat) instead of Poly (dip coat), although the dip coats have increased in quality lately with the AR companies using dip coats for their substrate coating. Hope this helps, Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr |
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