Prism Correction

[m0002a]

Is your blanket statement "In truth, many OD's don't do prism correction " based on your impression? I would beg to differ. My experience is most OD's would do more and not shy away from it. Their education emphasizes refractive as well as physiological issues of the eye which prism addresses. The MD is looking at much more than that and handling the referrals of medical not refractive problems from the optometrist.

Your question 2 needs to be more specific in that what type of prism are you referring to?. Slab off or another? The full rx would be helpful. The broad answer is normally the prism correction if slab off would be subtlety different (assuming lens measurements are consistent) but if not slab off some change is not unusual. The doc's will almost always error on keeping prism to its barest minimum and not "feed the beast".

Hope this helps.

I was asked for advise about this subject by someone I know who lives in another city than me. I was a little concerned that they had gone to a ophthalmologist instead of OD for a refraction (for same reasons as everyone else mentioned above), but they told me that they had a prism and only a few OD's or OP's in their city would refract a patient who comes in with an existing prism. This is in a city of approximately 500,000 people.

Regarding the second question. I don't have the specifics. The person told me that the patient was given a complete Rx with prism, but after some discussions with patient about reading habits or whatever, the ophthalmologist changed the add power (bi-focals) by .25, but did not adjust the prism. This made the patient suspicious and they asked me about it. I have no idea whether a change in add power would automatically require a different prism (not talking about two different refractions done at two different times), or whether the OP should have double checked the prism with the new add power.

[Robert Martellaro]

I have no idea whether a change in add power would automatically require a different prism (not talking about two different refractions done at two different times), or whether the OP should have double checked the prism with the new add power.

drk in post #8 answered you question in detail. I backed him up in post #25. drk is an experienced optometrist, and I fill prism Rxs all day long, almost everyday. You don't have to acknowledge and thank us for our help, but it's rude to act as if our advice did not occur.

[m0002a]

drk in post #8 answered you question in detail. I backed him up in post #25. drk is an experienced optometrist, and I fill prism Rxs all day long, almost everyday. You don't have to acknowledge and thank us for our help, but it's rude to act as if our advice did not occur.

Robert, my apologies if you were offended by anything I said or omitted.

Here is drk's response in post #8:

Thanks for the confidence in optometry. I hope we reciprocate the confidence in your profession.

Prism correction is not exact, so don't worry about the relationship between add power/working distance and prism. (This would only apply in a near vision only application, anyway.)

Secondly, the prism correction most of the time to be worn in distance and near gaze, and an add of whatever power has no bearing on the amount.

My comments:

1. I don't know who drk was responding to in his first sentence since he did not quote anyone. There is a lot of banter in this thread between posters, and most of it is not directly related to me.
2. My understanding from talking to patient is that the prism is in the reading area/near gaze of the person I am referring to, so I did not know what to make of drk's last comment. It is completely unfair for me to expect a definitive answer since he cannot examine or even talk to the patient. But I was not sure if his advice was applicable to this particular patient, so that was one reason I did not acknowdge his "answer."
3. Drk did respond, and I thank him for that, but ml43 basically said prism is over-prescribed and probably should not used in the vast majority of cases to begin with. I find that very interesting, but I have no idea who to believe.
4. My response was to Uncle Fester who did not seem to understand what I was saying about whether the prism would change if the add power changed. I was not responding to you or drk at that point, just trying to clarify for Uncle Fester. Admittedly, it is unfair to ask for advice when I am explaining a situation that I don't even have all the facts about, and I am not the patient.
5. Despite what a lot of people in this thread said (most of whom I trust a great deal), according to the patient, they had a very hard time finding any OD or OP who would refract someone with a prism. I am just getting this third hand, and don't know if that is correct, whether it is local phenomenon, or whether it is completely wrong.
6. Again, sorry for any confusion or if anyone was offended by my remarks.

[Wes]

1. My understanding from talking to patient is that the prism is in the reading area/near gaze of the person I am referring to, so I did not know what to make of drk's last comment. It is completely unfair for me to expect a definitive answer since he cannot examine or even talk to the patient. But I was not sure if his advice was applicable to this particular patient, so that was one reason I did not acknowdge his "answer."
2. Drk did respond, and I thank him for that, but ml43 basically said prism is over-prescribed and probably should not used in the vast majority of cases to begin with. I find that very interesting, but I have no idea who to believe.
3. My response was to Uncle Fester who did not seem to understand what I was saying about whether the prism would change if the add power changed. I was not responding to you or drk at that point, just trying to clarify for Uncle Fester. Admittedly, it is unfair to ask for advice when I am explaining a situation that I don't even have all the facts about, and I am not the patient.
4. Despite what a lot of people in this thread said (most of whom I trust a great deal), according to the patient, they had a very hard time finding any OD or OP who would refract someone with a prism. I am just getting this third hand, and don't know if that is correct, whether it is local phenomenon, or whether it is completely wrong.
5. Again, sorry for any confusion or if anyone was offended by my remarks.

DRK is an optometrist, and from what I've read of his posts, a very knowledgeable one. Optometrists tend to be the best refractionists, prism issues included. ml43 is a lab tech. Lab techs, with a few exceptions, tend to know little about refraction, and less about prism (for correction, not grinding it). Robert Martellaro is one of the most knowledgeable opticians on this board. Choose who you take your advice from wisely.

[m0002a]

DRK is an optometrist, and from what I've read of his posts, a very knowledgeable one. Optometrists tend to be the best refractionists, prism issues included. ml43 is a lab tech. Lab techs, with a few exceptions, tend to know little about refraction, and less about prism (for correction, not grinding it). Robert Martellaro is one of the most knowledgeable opticians on this board. Choose who you take your advice from wisely.

Thank you for your post. I think almost everyone agrees (and I stated it upfront) that OD's tend to be the best refractionists. But I appreciate you specifically saying "prism issues included." That was the piece of information I felt was missing from most of the posts about OD vs MD in this thread. I am very much aware of Robert's expertise, and I certainly did not want to leave the perception that I questioned his answer.

[ml43]

Please try not to take my post out of context or read too much into it.

my post was based on the assumption that you have a patient with prism, and does not currently have a optometrist/ophthalmologist they normally go to see.


I've seen many people who are perfectly happy with prescribed prism.

I have also seen just as many that see a different eye doctor every 6 months, and have 4-5 pairs of glasses they use, all with different rx and prescribed prism.

Most people with prescribed prism need their glasses, especially to read. And the slightest bad measurement or adjustment can alter the prescribed prism greatly depending on the power.



with all that said, yes, an optometrist will know what's best. Be it prescribed prism, VT, or surgery.

I am a little biased, because I used to work for a group of optometrists that would suggest a local VT specialist to people who showed signs of increasing prism, or new patients that needed prescribed prism.

I have seen prism reduced(I was the one cutting the job and dispensing).


What drk corrected me on was my wording(thank you for that, not what I was trying to say).
I did not mean to say I immediately suggest anyone with prescribed prism be checked by a vision therapist and an ophthalmologist for a surgical consult.

I was basing it on the premise that you had a new patient with prescribed prism asking for an eye doctor referral.
In that case, I would refer them to a vision therapist first, and possibly an ophthalmogolist.

Hope that clears up my original post.

[ml43]

DRK is an optometrist, and from what I've read of his posts, a very knowledgeable one. Optometrists tend to be the best refractionists, prism issues included.

Agree, the very few vision therapists I've met have been excellent with prism issues.

I'm not sure if it speaks for all of them, but I have been impressed with the ones I've met and worked with so far.

[drk]

I've learned so much from this "college of opticians" that any time an OD opinion is called for, I try to help, like "the Mensch" or FJP does.

1. Prism is not fussy in any way. Vertex distance, frame adjustment, whatever has no practical bearing.

2. It's hard/impossible to deliver prism in near gaze only, without one of a few options:
a. NVO specs with prism
b. decentered add
c. prism segs/Franklin BF
(Hopefully, someday someone will write a program for it for free-form lenses, somehow.)

However, working distance is never an issue. For example, we test for the need for prism at 40cm, like you would an add power. But while the increments of the add are in 1/4D, the increments in prism are relatively larger 1 prism diopters, so high precision is not possible.

3. Also, when prescribing prism, there is a lot of "slop", like making sausage. There are esoteric formulas, esoteric near point tests, and the tried-and-true "empirical" method, all of which are so variable as to be outside the range of accuracy of whether the patient is being tested at 30, 40, or 50 cm. In other words, adjusting the prism because the working distance of the add changed is absolutely unnecessary.

(Not to go down a rabbit trail, but if you think about it, raising an add power in an emerging presbyope does not necessarily force the patient to adapt to a new working distance anyway, but that's another conversation.)

4. Most prism is used throughout the distance and near portion of a lens (not in a near-only application, though we'd like to be able to do that) so changing add power will rarely affect a prescriber...only the amount needed for distance viewing is prescribed and that is independent of add power.

[erichwmack]

I have worked for MD's, OD's and an OD that specializes in VT. In my experience I have never seen an OD not be able to handle prism correction. In fact, the MD's would usually have the OD's (who worked in the same clinic) to refract the complex prism patients. In my experience OD's have a lot more refraction hours logged than MD's simply because of the other specialties that MD's are required to be proficient in. Thus OD's can refract the prism faster, usually.

To address your other part of the question. It really depends on what the prism is being prescribed for. There are types of prism like gaze or yoke prisms that don't have much of anything to do with the power of the lenses. So they wouldn't necessarily change. But then binocular prism corrections may change depending on the RX power change. If you think about how lenses fundamentally work (minus = apex to apex prism, plus = base to base prism) then as you gaze around to read a certain amount of prism is induced based on the power of the lens. As the RX changes the induced prism changes. So its completely possible to have to slightly adjust prism correction based off the rest of the lens.

[m0002a]

I have worked for MD's, OD's and an OD that specializes in VT. In my experience I have never seen an OD not be able to handle prism correction. In fact, the MD's would usually have the OD's (who worked in the same clinic) to refract the complex prism patients. In my experience OD's have a lot more refraction hours logged than MD's simply because of the other specialties that MD's are required to be proficient in. Thus OD's can refract the prism faster, usually.

To address your other part of the question. It really depends on what the prism is being prescribed for. There are types of prism like gaze or yoke prisms that don't have much of anything to do with the power of the lenses. So they wouldn't necessarily change. But then binocular prism corrections may change depending on the RX power change. If you think about how lenses fundamentally work (minus = apex to apex prism, plus = base to base prism) then as you gaze around to read a certain amount of prism is induced based on the power of the lens. As the RX changes the induced prism changes. So its completely possible to have to slightly adjust prism correction based off the rest of the lens.

Thank you for the reply. My understanding is that patient (not my patient) has had a prism to resolve double vision which worked well for a number of years, and experienced renewed intermittent double vision upon recently receiving a new Rx and being fitted with new lenses (slight difference in lens power, but prism the same). But patient still has intermittent double vision even when going back to old lenses. Patient is scheduled to see a neuro-ophthalmologist to diagnose the issue (MRI of brain was negative for any kind of tumor, etc).

[ml43]

Thank you for the reply. My understanding is that patient (not my patient) has had a prism to resolve double vision which worked well for a number of years, and experienced renewed intermittent double vision upon recently receiving a new Rx and being fitted with new lenses (slight difference in lens power, but prism the same). But patient still has intermittent double vision even when going back to old lenses. Patient is scheduled to see a neuro-ophthalmologist to diagnose the issue (MRI of brain was negative for any kind of tumor, etc).

I would highly suggest a VT consult, as another option to a surgery consult.

as long as the patient is willing to put in the time to do the exercises

hopefully drk can weigh in as well

[m0002a]

I would highly suggest a VT consult, as another option to a surgery consult.

as long as the patient is willing to put in the time to do the exercises

hopefully drk can weigh in as well

VT would definitely be preferable, but need a diagnosis first. I don't believe that the particular neuro-ophthalmologist selected is going to recommend surgery if there is any chance that VT is an option. Patient saw the same neuro-ophthalmologist for same condition in 1999, but double vision eventually went away on its own. Because patient is 90 years old, there may not be any good options available beyond patching one of the eyes to avoid double vision (which mostly occurs with patient's near vision).

[erichwmack]

Well I hope the best for the patient. Sometimes at that age treatments and therapies don't seem to work as well in my experience. The good news is that it only is intermittent at near only.