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Medical Forum / General / Vision / May 2007best-form spheric vs aspheric
I was told by my optician that there would always be a slight benefit to aspheric lenses. However, my research seems to indicate that a true best-form spheric is best. My question is, If someone has a prescription filled with a CR-39 lens, would they automatically be getting a best-form spheric? If not, how can a person make sure they are getting a best-form spheric? On 5/22/07 11:18 AM, in article 1179857932.768082.55450@q75g2000hsh.googlegroups.com, "infoseeker" <sheilasc@gmail.com> wrote: > I was told by my optician that there would always be a slight benefit > to aspheric lenses. However, my research seems to indicate that a > true best-form spheric is best. My question is, If someone has a > prescription filled with a CR-39 lens, would they automatically be > getting a best-form spheric? If not, how can a person make sure they > are getting a best-form spheric? The real question is: Best for what? Lens design is always a trade-off. That applies even for simple lenses. For example, how much do you value best resolution looking straight ahead along the axis of your lens compared to facing straight ahead and pivoting your eyes to see in and off-axis direction? Lens designers use some kind of merit function that is a weighted average of all kinds of performances. Such a merit function is often subjective. With that merit function, a lens can be designed to maximize it under whatever fabrication constraints there may be. It is like asking what combination of spices will give the best taste to chili. Fortunately, it is usually not necessary to go to such extremes. Bill -- Fermez le Bush--about two years to go. > On 5/22/07 11:18 AM, in article > 1179857932.768082.55...@q75g2000hsh.googlegroups.com, "infoseeker" [quoted text clipped - 23 lines] > Bill > -- Fermez le Bush--about two years to go. The reason I ask is that my mother has macular degeneration. She can still see to carry out daily activities, but she is starting to lose central vision. I am trying to determine what type of lens will give her the widest field of clear vision. On 5/22/07 6:29 PM, in article 1179883756.743107.213850@o5g2000hsb.googlegroups.com, "infoseeker" <sheilasc@gmail.com> wrote: > The reason I ask is that my mother has macular degeneration. She can > still see to carry out daily activities, but she is starting to lose > central vision. I am trying to determine what type of lens will give > her the widest field of clear vision. I am not a health professional, but you do not have to be one to understand that her problem arises from her retina and not from the optics of her eye and associated external lenses. It is likely that a health professional working with macular degeneration may have a few tricks of the trade that might eke out a bit of performance by fine tuning the optics. I would not expect much improvement, but you have nothing to lose by asking. Your best bet might be to use television to give extra magnification of printed pages. Bill -- Fermez le Bush--about two years to go. > On 5/22/07 11:18 AM, in article > 1179857932.768082.55...@q75g2000hsh.googlegroups.com, "infoseeker" [quoted text clipped - 23 lines] > Bill > -- Fermez le Bush--about two years to go. The reason I ask is that my mother has macular degeneration. She can still see to carry out daily activities, but she is starting to lose central vision. I am trying to determine what type of lens will give her the widest field of clear vision. > On 5/22/07 11:18 AM, in article > 1179857932.768082.55...@q75g2000hsh.googlegroups.com, "infoseeker" [quoted text clipped - 23 lines] > Bill > -- Fermez le Bush--about two years to go. The reason I ask is that my mother has macular degeneration. She can still see to carry out daily activities, but she is starting to lose central vision. I am trying to determine what type of lens will give her the widest field of clear vision. > On 5/22/07 11:18 AM, in article > 1179857932.768082.55...@q75g2000hsh.googlegroups.com, "infoseeker" [quoted text clipped - 23 lines] > Bill > -- Fermez le Bush--about two years to go. The reason I ask is that my mother has macular degeneration. She can still see to carry out daily activities, but she is starting to lose central vision. I am trying to determine what type of lens will give her the widest field of clear vision. > On 5/22/07 11:18 AM, in article > 1179857932.768082.55...@q75g2000hsh.googlegroups.com, "infoseeker" [quoted text clipped - 23 lines] > Bill > -- Fermez le Bush--about two years to go. The reason I ask is that my mother has macular degeneration. She can still see to carry out daily activities, but she is starting to lose central vision. I am trying to determine what type of lens will give her the widest field of clear vision. > On 5/22/07 11:18 AM, in article > 1179857932.768082.55...@q75g2000hsh.googlegroups.com, "infoseeker" [quoted text clipped - 23 lines] > Bill > -- Fermez le Bush--about two years to go. The reason I ask is that my mother has macular degeneration. She can still see to carry out daily activities, but she is starting to lose central vision. I am trying to determine what type of lens will give her the widest field of clear vision. >I was told by my optician that there would always be a slight benefit >to aspheric lenses. However, my research seems to indicate that a >true best-form spheric is best. Aspherics should be "best form" also. On and off-axis vision is the same with both types of lenses as long as they are fit properly. >My question is, If someone has a >prescription filled with a CR-39 lens, would they automatically be >getting a best-form spheric? Only if the lab uses the base curve that the lens manufacturer recommends. >If not, how can a person make sure they >are getting a best-form spheric? Top quality labs will always use the recommended curve. You can get pretty good idea if the curve is correct by using a lens clock to measure the base curve, and then check with the lab or lens manufacturer. >The reason I ask is that my mother has macular degeneration. She can >still see to carry out daily activities, but she is starting to lose >central vision. I am trying to determine what type of lens will give >her the widest field of clear vision. Avoid polycarbonate if the Rx is above three diopters or so, don't use small frames or frames with wide temples, use segmented multifocals (lines) instead of progressives, especially if the Add for reading is above +2.75, and see a low vision specialist. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman |
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