Progressive lenses vs bifocals
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Progressive lenses vs bifocals
Probably need to add some sort of correction for reading soon( already use glasses for distant vision), and just wondering on people's experience in flightdeck with Progressive lenses
Uncle Pete
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I started wearing specs for reading and found varifocals worked very well. I had plain glass for distance work with a half tint on the upper half which made it sun specs for outside and clear for reading, absolutely brilliant.
I do know of people that haven't coped with varifocals and they aren't for everyone. You also have to take great care not to bash them around once they're set up properly.
Good luck!
I do know of people that haven't coped with varifocals and they aren't for everyone. You also have to take great care not to bash them around once they're set up properly.
Good luck!
I had a cataract removed at 28. Cataract removal involved implanting a fixed focus perspex lens to replace the damaged natural lens, leaving me with completely fixed focus in the affected eye. As a result, I developed quite an interest in multifocals (bifocals, trifocals and progressive lenses).
One day I was discussing their relative merits with an optometrist friend, who told me that someone had done some careful research about multifocal lens type preferences. They apparently took a large group of first time multifocal users and randomly allocated half each to bifocals and to progressive lenses. Then, after six weeks, they reversed the allocations, so that those who started with bifocals got to experience progressives and vice versa.
And the result? He said that they overwhelmingly preferred whichever they had experienced first!
In addition to having had a cataract removed, I also have strabismus; my eyes do not converge correctly and I can choose which to see, while retaining normal peripheral vision in the other. It's quite seamless and doesn't bother me in the slightest; I can swap my attention between eyes at will and in mid-task, but I can no longer see 3d effects which depend on stereopsis (slightly different images to each eye).
Furthermore, for various reasons related to my complicated optical history, I tend to use each eye for different sorts of tasks, and the base script (for distance vision) for each eye is quite different. So I find bifocal or trifocal lenses best for one eye and progressives for the other.
Why?
My right eye has a base script of about -4 spherical (quite short sighted) with very little cyl (astigmatism), and I find that a progressive lens works well for that eye. It's also the eye I favour for very close detail work, by simply removing my specs entirely.
My left eye, which has had a fixed focus lens implant, has about -2.5 cyl (cylindrical, eg: astigmatism) as a result of the inexperience of the surgeon who was learning on me. I've found that a progressive lens overlaid on a script with a lot of cyl has quite poor characteristics, with a very narrow strip down the centre which works well. After years of unsatisfactory progressive lenses, I got a pair of "single vision" glasses for using a computer and realised I could read with my dominant left eye again; to my great relief. Since then, I've had only bifocals and trifocals for that eye and I've been very happy with them. Meanwhile, my right eye, which retains some accommodation (ability to change focus; I'm 52 now, and my right eye is aging normally) continues with progressives which work seamlessly for me.
The main issue I see with progressives is the quality of vision, and the width of the band down the middle of the lens which gives an acceptable result.
Discuss this issue with your optometrist; different brands of lens use different algorithms, while large cylindrical components, used to treat astigmatism, can also seriously affect useability.
Also, for reference, for my left, fixed focus eye, I find a +1.5 correction suits reading a computer screen which is at arms length away, and +2.5 is suitable for reading books and close up work. Since trifocals are only available with evenly spaced steps, I end up with 0/+1.25/+2.5 for "outside" specs, while using +1.5/+2.5 bifocals for indoor/computer/dinner table specs.
Presumably you are simply over 45 and have some residual accommodation, but even so, have a think about what distances particularly matter to you, eg: for instrument panels, using a laptop, etc. Seriously consider dedicated specs for different tasks. Apparently lenses with reading sections at the top for reading overhead instruments are possible, for example.
One last thought; those people who had laser surgery when they were 30 to cure their myopia (short/near sightedness) and rid themselves of glasses? At 45 they suddenly discover they need to buy and carry reading glasses, while untreated myopes simply take their specs off to see close up detail.
One day I was discussing their relative merits with an optometrist friend, who told me that someone had done some careful research about multifocal lens type preferences. They apparently took a large group of first time multifocal users and randomly allocated half each to bifocals and to progressive lenses. Then, after six weeks, they reversed the allocations, so that those who started with bifocals got to experience progressives and vice versa.
And the result? He said that they overwhelmingly preferred whichever they had experienced first!
In addition to having had a cataract removed, I also have strabismus; my eyes do not converge correctly and I can choose which to see, while retaining normal peripheral vision in the other. It's quite seamless and doesn't bother me in the slightest; I can swap my attention between eyes at will and in mid-task, but I can no longer see 3d effects which depend on stereopsis (slightly different images to each eye).
Furthermore, for various reasons related to my complicated optical history, I tend to use each eye for different sorts of tasks, and the base script (for distance vision) for each eye is quite different. So I find bifocal or trifocal lenses best for one eye and progressives for the other.
Why?
My right eye has a base script of about -4 spherical (quite short sighted) with very little cyl (astigmatism), and I find that a progressive lens works well for that eye. It's also the eye I favour for very close detail work, by simply removing my specs entirely.
My left eye, which has had a fixed focus lens implant, has about -2.5 cyl (cylindrical, eg: astigmatism) as a result of the inexperience of the surgeon who was learning on me. I've found that a progressive lens overlaid on a script with a lot of cyl has quite poor characteristics, with a very narrow strip down the centre which works well. After years of unsatisfactory progressive lenses, I got a pair of "single vision" glasses for using a computer and realised I could read with my dominant left eye again; to my great relief. Since then, I've had only bifocals and trifocals for that eye and I've been very happy with them. Meanwhile, my right eye, which retains some accommodation (ability to change focus; I'm 52 now, and my right eye is aging normally) continues with progressives which work seamlessly for me.
The main issue I see with progressives is the quality of vision, and the width of the band down the middle of the lens which gives an acceptable result.
Discuss this issue with your optometrist; different brands of lens use different algorithms, while large cylindrical components, used to treat astigmatism, can also seriously affect useability.
Also, for reference, for my left, fixed focus eye, I find a +1.5 correction suits reading a computer screen which is at arms length away, and +2.5 is suitable for reading books and close up work. Since trifocals are only available with evenly spaced steps, I end up with 0/+1.25/+2.5 for "outside" specs, while using +1.5/+2.5 bifocals for indoor/computer/dinner table specs.
Presumably you are simply over 45 and have some residual accommodation, but even so, have a think about what distances particularly matter to you, eg: for instrument panels, using a laptop, etc. Seriously consider dedicated specs for different tasks. Apparently lenses with reading sections at the top for reading overhead instruments are possible, for example.
One last thought; those people who had laser surgery when they were 30 to cure their myopia (short/near sightedness) and rid themselves of glasses? At 45 they suddenly discover they need to buy and carry reading glasses, while untreated myopes simply take their specs off to see close up detail.
Last edited by nonsense; 11th May 2015 at 13:37.
Psychophysiological entity
In addition to having had a cataract removed, I also have strabismus;
Está servira para distraerle.
If by progressive lenses you mean varifocals, they didn't work for me. Trifocals do work well though, especially at night when one has to alternate vision perspective between a dimly lit overhead panel and a screen in front of one's nose.
One of the problems inherent in a two crew cockpit is that panel lighting has to suit both parties. As the older and blinder crew member, I always deferred to the interior illumination requirements of the gumball in the right.
Trifocals are an expensive option and my spare glasses, within handy reach of course, were never quite as superior as my premier pair. Incidentally, stupid as it might look, a spectacle suspender is a good idea when trailing a few hundred £s of kit around one's glazed eyeballs.
One of the problems inherent in a two crew cockpit is that panel lighting has to suit both parties. As the older and blinder crew member, I always deferred to the interior illumination requirements of the gumball in the right.
Trifocals are an expensive option and my spare glasses, within handy reach of course, were never quite as superior as my premier pair. Incidentally, stupid as it might look, a spectacle suspender is a good idea when trailing a few hundred £s of kit around one's glazed eyeballs.
Originally Posted by Loose rivets
Later I get the hint that this <strabismus> occurred after and because of the new lens. Is this the case?
I always had some level of amblyopia (right eye weak) and was prone to convergence insufficiency at distance, but not close up, even as a child.
When my cataract developed I was studying the first year of an engineering degree, and as my vision in my left eye deteriorated, I learnt to get on ok (not great...) with my right eye. With the lens implant we attempted to give my left eye good uncorrected distance vision, but the surgeon overlapped the cornea tissue slightly too much (or maybe not enough) when closing up, resulting in tension which flattened my cornea on one axis - hence 2.5 diopters of cyl where once there was none.
At that stage, although it was suggested I might experience problems, I still converged OK most of the time.
Then four years later, six weeks before the end of my engineering degree I suffered a detached retina in my left eye. Risk factors include male, ~30yo, myopia, cataract surgery, laser capsulotomy (treatment for a complication of the cataract surgery). The only risk factor I didn't have was bungy jumping! I spent the final six weeks of my degree with my good eye patched, and without a period of adjustment, I struggled with things like reading. Driving was definitely right out!
When the patch came off, my eyes no longer converged at all. I could sort of push them to converge, but it was just uncomfortable, a bit like trying to cross your eyes, so I didn't.
So it wasn't a direct result of cataract surgery and it certainly isn't a typical effect of cataract surgery, which for anyone here who might find themselves facing it, is one of the safest and most successful surgeries around, with an absurdly high success rate. It is said to be one of the most satisfying surgeries to perform, if somewhat boring, because patients are almost universally delighted with the outcome.
The weekend before my surgery I was (trying to) fly a hang glider. As a novice, I was having enormous difficulty judging the flare over a featureless beach with only one eye, and at one stage, sitting in the shade of the glider eating lunch, I closed my good eye and could not even detect the colour of the glider fabric with the sunshining through it. The day after my surgery, they took the patch off my eye and I could see the doctors newspaper on his desk on the far side of the room in glorious living colour. That's not something you forget.
progressives
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I'm finding my progressive (or continuous) focus specs are working out well. I was a bit concerned at the concept because I've always liked to have 'perfect' refraction correction but, eventually, the convenience factor won me over. I did however spend a small fortune on high-index lenses with state-of-the-art distortion correction. The latter feature is important to me, particularly for reading iPADs, charts etc. I hate seeing rectangles as any other shape.
Noting my disposition to optical perfection my optometrist spent a long time geting the optical centres just right, and we did a few zonal specifications based on instrument panel distances etc. It's all worked out well although maybe making the 'reading' zone a tiny bit larger would have been an improvement for reading in bed. The only other limitation is some chromatic aberration at the extreme edge of the field, which I tolerate better than any shape distortion. My lenses are Hoya brand, and I was impressed with their quality control when the lab threw the first attempt away, recommending a slightly lower index material to properly match the optometrist's specification. As I recall there is some clever optics in which horizontal and vertical distortion is corrected on different lens surfaces.
Anyway, it works!
Noting my disposition to optical perfection my optometrist spent a long time geting the optical centres just right, and we did a few zonal specifications based on instrument panel distances etc. It's all worked out well although maybe making the 'reading' zone a tiny bit larger would have been an improvement for reading in bed. The only other limitation is some chromatic aberration at the extreme edge of the field, which I tolerate better than any shape distortion. My lenses are Hoya brand, and I was impressed with their quality control when the lab threw the first attempt away, recommending a slightly lower index material to properly match the optometrist's specification. As I recall there is some clever optics in which horizontal and vertical distortion is corrected on different lens surfaces.
Anyway, it works!
For what its worth I tried both, varifocals first but could not get on with them & have used bifocals since. When I talked this over with my optician he reckoned that it was because I did not have to wear the varifocals all the time (only when driving or flying) so the brain would take a lot longer to adapt to them.
Tried Varifocals for several months but had to bend my head down to see obstacles when walking which gave me problems with my neck; one also has to pay particular attention when driving and using the door mirrors.
There was also the problem that I had to turn my head when reading as except for the distance part the field of view in focus was very limited.
Bifocals were much better in both respects - the distance part of the lens cut off was lower and the field of view in the reading prescription part of the lens was wider.
On both occasions I had two pairs - one plain and one polaroid sun glasses.
Unfortunately the reading prescription was set at 30cm in my normal glasses which is too close...the Shades I had made with a focal length of 50cm.
I still alternate between carrying three pairs of single vision glasses.
I've also lost most of my power of accommodation.
I should add that although I still fly I don't fly commercially any longer so maybe this is a "thread drift"...
good luck
There was also the problem that I had to turn my head when reading as except for the distance part the field of view in focus was very limited.
Bifocals were much better in both respects - the distance part of the lens cut off was lower and the field of view in the reading prescription part of the lens was wider.
On both occasions I had two pairs - one plain and one polaroid sun glasses.
Unfortunately the reading prescription was set at 30cm in my normal glasses which is too close...the Shades I had made with a focal length of 50cm.
I still alternate between carrying three pairs of single vision glasses.
I've also lost most of my power of accommodation.
I should add that although I still fly I don't fly commercially any longer so maybe this is a "thread drift"...
good luck
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The first time I tried multis I couldn't stand them - that was for about a month, BUT, I think it was because the field of view in focus close up was a lot narrower than I was hoping or expecting. So I carried on with one pair for distance and one for close up/reading.
I typically drove and flew wearing the distance glasses. The only problem with that was the dash in the car and the instrument panel in the planes wasn't in focus and I was often straining to see what was being indicated exactly. I could see the dials and pointers and had a good idea of where they were in relation to where they should be but it was not easy. And of course in lower light situations (cloudy/overcast or late afternoon near sunset for flying or night time driving) the depth of field due to a larger iris was a lot less.
My accommodation ability continued to decrease to the point where it was non-existent. I got my eyes retested a couple of years later and tried the multis again and haven't looked back (except in the mirrors and when I turn my head).
I'm pretty sure this pair has a slightly wider close up field of focus but I still use a reading pair for any serious reading due to the having to continually move the head to read anything wider than a normal newspaper column.
I heartily endorse multis but would continue to wish for a wider field in focus close up.
I typically drove and flew wearing the distance glasses. The only problem with that was the dash in the car and the instrument panel in the planes wasn't in focus and I was often straining to see what was being indicated exactly. I could see the dials and pointers and had a good idea of where they were in relation to where they should be but it was not easy. And of course in lower light situations (cloudy/overcast or late afternoon near sunset for flying or night time driving) the depth of field due to a larger iris was a lot less.
My accommodation ability continued to decrease to the point where it was non-existent. I got my eyes retested a couple of years later and tried the multis again and haven't looked back (except in the mirrors and when I turn my head).
I'm pretty sure this pair has a slightly wider close up field of focus but I still use a reading pair for any serious reading due to the having to continually move the head to read anything wider than a normal newspaper column.
I heartily endorse multis but would continue to wish for a wider field in focus close up.
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It is/will be what you get used to!
All I would add is to ensure that the 'reading' part of a varifocal lens is large enough and not too far down the lens itself. This applies especially to 'aviator' style spectacles
All I would add is to ensure that the 'reading' part of a varifocal lens is large enough and not too far down the lens itself. This applies especially to 'aviator' style spectacles
