Prism 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

 

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

 

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.

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

 

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:



Thank you!

 

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

 

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