+18 post cats

[Bohumila]

Hi everyone, I posted this elsewhere on this site, then realised this is place it should be:

Robert Martellaro referred me to this site, thinking that your collective expertise might be helpful to me. I'm a +18 aphakic who is dpendent on glasses for everything. My acuity is quite good--better than 20/20, in fact--but I have almost no peripheral vision due to the ring scotoma. With the usual lentics, I am lucky to see more than 15 degrees to the side (or so it seems). I recently got a pair of full-field glasses made using a 15-base Signet Armorlite Hyperaspheric blank with a +3 back curve. The improvement in peripheral vision is enormous!! I can now walk down the store aisle wothout having to stop every few feet to get my bearings, and don't bump into people on crowded sidewalks (or at least not as much as usual). The optics are not ideal, in that there is no cyl in these lenses (I have about 1.00 cyl ou) and the vertex adjestment is not perfect. (Since the lens sits further away, I need to dial down the back curve to about +2 or so.) However, this is trivial amounts of fine-tuning compared to the benefit of being able to function more-or-less normally.

Does anyone here have experience making bi-convex lenses? If so, I would sure love to chat.
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[Darryl Meister]

Why do you want bi-convex lenses?

Best regards,
Darryl

[HarryChiling]

I have surfaced a convex back curve on a lens it is not to different to do other than the fact that the tool usually has to be made and sometimes I have to use a razor blade to cut out parts of my pads to have them fit on the tool without bulges and folds. Soot me a message if you have any questions.

[Bohumila]

The biggest problem us high hyperopes face is lack of peripheral vision. The biconcave lenses allow for a full field lens, which otherwise is not possible in my script. Since there are so few of us, there is no real incentive for anyone to make specialty lenses in this script, so there are not many options. A few months ago I convinced a specialty lab to make a biconcave full field lens, and the results are tremendous. Most severe hyperopes just put up with very limited vision, which I will always have to as well, but these full field lenses are an order of magniture better than my lentics, which give me barely functional vision.

I know all the textbooks tell a different story, but I doubt any of the textbook writers have to wear this script. I am desparate to get a decent pair of glasses, and to find a reliable source for these glasses. Beleive me, for those of us who have no other options, full field lenses are a Godsend.

[Darryl Meister]

I can certainly see how you could have problems finding suitable lens designs for your prescription, but a biconvex lens will generally provide you with a narrower field of clear vision and more distortion than a lens with a slightly concave back curve (assuming you can find a high enough base / front curve to accommodate a slightly concave back).

There are also designs available that employ more sophisticated aspheric surfaces. These surfaces are designed to provide clear optics in the central region of the lens, but then gradually taper off into a carrier curve in the periphery without the "bowl" of a lenticular. These lenses are comparable in thickness and weight to lenticulars, but provide the cosmetic benefits and reduced scotoma (blind area) of a full-field design. The Rodenstock Perfastar comes to mind, which is also available in a base curve suitable for your prescription. (Essilor makes a Super Modular, but I don't know that it comes in a high enough base curve.)

However, if you're reasonably happy with what you're wearing now, you may or may not want to continue experimenting with potentially expensive lenses. If you could find someone who could demonstrate some of these various designs for you, that would be ideal.

Best regards,
Darryl

[Bohumila]

Many thanks, Darryl--WHat I have now works great. I have tried some of the lenses you suggested, and they are better than the simple lentcs, though the blended types have their own set of problems.

My glasses now are really great (relatively speaking). They are in a very large frame (54), semi-aviator shape, and give me the best visual field I have ever had. I know it's nothing like normal vision, but I am far more functional with them. With a bit of fine-tuning, these will work fine. I just need to add the cyl and maybe go back to a plastic frame.

Thanks for the ideas!