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Medical Forum / General / Vision / March 2005Prism glasses for exotropia?
My left eye has been exotropic, since my teens. It was never corrected fully. I am also quite shortsighted with astigmatism. With my full prescription, my eye normally focuses fine, but still wanders off when tired. I'd like to know if wearing prism glasses would help the weak eye to focus. If there is someone or something in my side vision, I find my eye veers off, without my turning my head, in their direction instead of looking straight ahead. This is so frustrating. Has anyone else had the same problem as me? My optometrist never prescribed these glasses in the past, but then again my last optometrist said I didn't even have a lazy eye so... Any advice is welcomed. Prism in spectacle lenses are not to help in "focusing" but rather to keep the eyes in proper alignment. In your case, it really depends upon the amount of fusion (ie. binocularity- how the two eyes are working together) if prism can be of help. Seeing someone familar in treating strabismus for an opinion would be your best bet. If the "wandering eye" is 20/20 corrected, it would not be considered amblyopic (ie "lazy"). frank >Prism in spectacle lenses are not to help in "focusing" but rather to >keep the [quoted text clipped - 10 lines] > >frank Dr. Frank, If--as in my case, you have a pretty darned inadequate or dysfunctional accommodative system--wouldn't it be true that *wearing the appropriate prism* to correct an exotropia *could* reduce load on the accommodative mechanism, actually *facilitating* focusing, especially at near? I'm thinking of the near vision triad: accommodation > convergence > pupillary miosis. Without the prism, an excess of accommodation would be needed to overcome the exo- even before focusing. Correct? Neil >>Prism in spectacle lenses are not to help in "focusing" but rather to >>keep the [quoted text clipped - 18 lines] > the accommodative mechanism, actually *facilitating* focusing, > especially at near? Don't confuse focus (clear vision, achieved at near by accommodation) with fusion (single vision, achieved at near by convergence). Prism helps with fusion but does nothing for focus. > I'm thinking of the near vision triad: accommodation > convergence > > pupillary miosis. Without the prism, an excess of accommodation would > be needed to overcome the exo- even before focusing. When the eye accommodates to clear an object at near it also converges; if the convergence is not exact and single vision is not achieved, then convergence changes (independant of accommodation) to achieve single vision. Convergenance can be changed without changing accommodation but a change in accommodation always causes a change in convergence. Accommodation in excess of that needed for the viewing distance would cause blur. It is true that sometimes a person with a large exophoria may over accommodate thus achieving single, blurred vision and this may be a cause of pseudomyopia, however, this is rare and more likely seen with exophoria, not exotropia. Exotropes are likely to accommodate correctly and suppress the second image, thus achieving single, clear vision. A person with poor accommodation may have a large exophoria at near due to the lack of accommodative convergence. In that case, prism will solve the exophoria but will not help the poor accommodation and only single, blurred vision is achieved. If your personal problem is accommodative dysfunction without a large exophoria or exotropia then prism will make no difference at all, you will converge less with prism but accommodation is still dysfunctional. You have single, blurred vison without prism and single, blurred vision with prism. Dr Judy > Correct? > > Neil >> frank > [quoted text clipped - 13 lines] > > Neil No. Accommodation does not happen "without focusing". Accommodation IS focusing. So, if an excess of accommodation is required, yet get too much focusing, that is, one should focus inappropriately closer than needed. Thank your for your responses, but if possible I would like to hear the experiences from people who suffer from the same problem ... Does anyone have a picture of what prism glasses look like. I may need them and want to know what they look like. I am shortsighted, have astigmatism and my left eye is exotropic. I can't remember whether it is a base-in or base-out prism I need. If anyone out there has a similiar prescription and is also exotropic, could you please send me a private mail telling me about your experiences: nicoleh76@gmail.com Thank you! > >> frank > > [quoted text clipped - 17 lines] > focusing. So, if an excess of accommodation is required, yet get too much > focusing, that is, one should focus inappropriately closer than needed. >Thank your for your responses, but if possible I would like to hear >the experiences from people who suffer from the same problem ... [quoted text clipped - 7 lines] >could you please send me a private mail telling me about your >experiences: Nicole, You need base-in prism. Do you have the actual prescription? I can tell you that I'm very farsighted, have a moderate amount of astigmatism, and am exotropic, more so at near than at distance. A *few* diopters of prism don't detract much from eyeglasses. If you're up in the double digits (10d or more), it can get a bit ugly. *If* you have a fairly strong prescription for your myopia and/or astigmatism, you may be able to wear contact lenses to correct the underlying refractive error, then wear prism-only glasses over the contacts. The doctor can likely divide the base-in prism equally between your two eyes, further reducing the cosmetic effect of the lens. For example: if you need 8d of base-in, the doc will usually prescribe 4d worn in each eye. The new high-index lenses are pretty incredible. They get a lot of power out of pretty thin pieces of plastic. The glasses made for me are pretty darned nice looking. Sending a pic without understanding how your Rx compares to mine won't tell you much. Suffice to say, they just look like eyeglasses :-) > Thank your for your responses, but if possible I would like to hear > the experiences from people who suffer from the same problem ... [quoted text clipped - 7 lines] > could you please send me a private mail telling me about your > experiences: Your first step is to ask your eye doctor if prism will do anything for you. If you are suppressing or amblyopic, prism will not stop the wandering. If prism will help, then you may also need to have vision training to learn to control the wandering eye. You also need to know how much prism is required, as the appearance of the glasses will depend upon the amount of prism. Two to four prism diopters will not be noticable, but larger amounts will be and very large amounts may require a Fresnel lens which degrades optical quality. Base in prism, the kind you need, results in the lens edge being thicker towards the nose. The amount of prism required totally depends upon your individual situation and comparison to other people with different amounts will not yield useful information. Dr Judy > nicoleh76@gmail.com > [quoted text clipped - 21 lines] >> focusing. So, if an excess of accommodation is required, yet get too much >> focusing, that is, one should focus inappropriately closer than needed. |
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