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prisms

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traumaemt

Posts: 72

Joined: Wed Jan 09, 2013 2:58 pm

Location: U.S.A.

Post Thu Jan 10, 2013 6:04 am

Re: prisms

The only problem I am having ordering from zenni is that I need double prisms in my glasses.

OD 4DN 3U
OS 4DN 3D

I was going to get some stronger sphy in my glasses, but I want to have my prism in it. That is my true rx for prism. the rest is:

OD -1.75x-0.25x5
OS -1.5

Does anyone know if I can ask zenni if they will add both prisms to the lens?

Thanks
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Cactus Jack

Posts: 100

Joined: Sat Sep 24, 2011 3:00 pm

Post Thu Jan 10, 2013 6:52 am

Re: prisms

I am having trouble understanding the prism part of your prescription. Are you sure that is correct.
It is not unusual to have horizontal prism (Base In (BI) or Base Out (BO) in the same prescription as vertical prism (Base Up (BU) or Base Down (BD))
Is the 4DN an abbreviation for BI or BO in a language other than English?
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traumaemt

Posts: 72

Joined: Wed Jan 09, 2013 2:58 pm

Location: U.S.A.

Post Thu Jan 10, 2013 3:57 pm

Re: prisms

No, that is correct. my eyes are weird because of Multiple Sclerosis. My Right eye looks down and right. My Left eye looks up and left. If I was to put it as a diagram with the letter A, the middle one in the center, where my eyes should be focused, and the outer ones will be where my eyes are looking:

A----
--A----
-----A----

I know this is weird, but that is how my eyes are, for now. They have been constantly changing. 3 months ago, I only had 2dn prisms, and plano with -0.25x5 OD and plano OS. That is how fast I am changing. 6 months before that, I had OD -.75x-1.0x25 and OS -0.50. So who knows what will happen in a few months. But it is getting too expensive to keep going to the optometrist every time. So, I am going to try and handle it myself. Glasses are cheap on the internet, not like the $140 lenses only I have now.

Sorry, I meant BI (Base In). My Doc wrote as BN.
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Cactus Jack

Posts: 100

Joined: Sat Sep 24, 2011 3:00 pm

Post Thu Jan 10, 2013 5:20 pm

Re: prisms

OD Sphere -1.75 Cylinder -0.25 Axis 5 Prisms 4 BI 3 BU
OS Sphere -1.50 Cylinder (leave blank) Axis (leave blank) Prisms 4 BI 3 BD

Would not be an unusual prescription. That is how oblique prism would be specified for a situation such as yours. You might have to list the complete Prism information in a Remarks or Special Instructions box.

It will be interesting to see how Zenni will react to your order.

May I ask where you live?
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traumaemt

Posts: 72

Joined: Wed Jan 09, 2013 2:58 pm

Location: U.S.A.

Post Thu Jan 10, 2013 5:21 pm

Re: prisms

Kansas

My doc is a young guy. I don't know if this is how they are teaching these days, but the optical people understood it. Maybe there is just 2 different ways of writing it.
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turborob082

Posts: 13

Joined: Fri Dec 28, 2012 1:20 am

Post Sat Jan 12, 2013 1:00 am

Re: prisms

Thanks for the explanation cactus, Hopefully the -.5 glasses are delivered soon and I can gauge how helpful they are and if i want to add prism to them or not.

traumaemt
I think zenni will be able to do the double prism, I ordered a pair from goggles4u with both BI and BD prisms, I simply spoke to their customer service and later specified it in my order. Goggles doesn't charge extra for prisms nor do they have a section in their ordering form, one has to simply write it under optional comments. I recently received a pair that where made in my neuro ophthalmologists office and can say that there is a slight difference between the glasses. don't get me wrong, the ones from goggles4u are more than acceptable but you should expect a greater margin of error from these companies. Also if you are in the process of changing lenses every few months or like me who is trying to self diagnose(doc only helped so much) the online way is much much cheaper. I believe one can get a pair for under $30 delivered vs the $400 that I recently paid.
Best of luck, if you do order glasses with prisms from zenni let us know how they come out.
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traumaemt

Posts: 72

Joined: Wed Jan 09, 2013 2:58 pm

Location: U.S.A.

Post Wed Jan 16, 2013 1:02 am

Re: prisms

turbo, will do. I will try to order them soon funding is an issue right now. medical stuff is draining me right now due to the new year and co pays and deductibles. I have MS, and one of my scripts is $4600 for a 28 day supply cash price. With insurance, it is $3000 in January, but free for the rest of the year, along with the rest of my 11 other meds and other supplies. So it may be next month, but I will try!! Thanks!!
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turborob082

Posts: 13

Joined: Fri Dec 28, 2012 1:20 am

Post Wed Jan 16, 2013 4:32 pm

Re: prisms

Wow, those are really expensive meds. be well, wish you the best with what your dealing with.
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canpaixano

Posts: 23

Joined: Tue Sep 27, 2011 9:33 am

Location: Switzerland

Post Thu Aug 15, 2013 11:17 am

Re: prisms

Hi all

It's been a while. And I have some news regarding my prism journey.
First of all, as you might remember, I currently have 20 pdpt base out in each lense, glasses for hyperopia and an add of +1.5 in my glasses.
A few days back I went to my annual exam and had a new ecp, the old one had apparently left the company, so I was rather critical regarding the new one.
Well, it turns out that there's been some changes. After carefully measuring and examining my eyes he came to the conclusion that I had in fact too many prisms in my current glasses.
He said that I would in fact only need the 24 prisms (12 in each lens) according to the result of the exam. He then asked me if I felt comfortable seeing through the trial frame which I did indeed.
It is not that surprising since I had felt some discomfort over the last few months but I had rather thought that this had to do with a need for higher prisms. Well, sometimes you're in for a surprise.
Additionally to the fact that I was now back to the amount of prisms I had had a few years back he announced that I now also had a few prisms base up in my right eye. Not that this was enough news, he also said that due to my age he did not think too much of my add and thought that I should still be able to accommodate accordingly. I'm not sure about that. But I'll have another exam next week where he wants to double check the amount of prisms he has detected a few days back. He also said that then he would take on measuring the amount of prisms I need up-close. He said that he is of the opinion than before giving an add he would rather prescribe more prisms for close-work. Does that make sense? I mean: when I'm reading I already turn my eyes inwards a bit naturally, everybody does. So how come I need a higher amount of prisms for up close? I don't quiet understand.
Also, can anybody comment on my newly measured base-up prism? I'm not very familiar with prisms base up or down and can't seem to find anything online. There is vast information about esophoria, exophoria and such, but can somebody help me out here?
I'll keep you posted after my next exam next week.
Best,

C.
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duncanw

Posts: 2

Joined: Sun Oct 20, 2013 1:53 pm

Post Sun Oct 20, 2013 2:04 pm

Re: prisms

Ok, I am fairly new to prism lenses and would appreciate some insight.

I wore contacts for years, sadly when I turned 30 I started to see double.
The military told me that it is likely the result of an injury sustained during hand to hand training back in 2004 and that my eyes lost their ability to compensate for a sixth nerve palsy due to my age.

In December 2012, I received my first prism prescription. Base out 3 in each eye. I deployed to Afghanistan in 2013 (where I am now), and my double vision returned.... I found one of the few eye doctors in country, and received a new prescription raising my prism to 5 base out in each eye. He also told me that I might need additional prism in the future, as my misalignment is 16 rather then 10.

Why didn't he prescribe me 8 base out in each eye? I buy my own glasses as the military ones are.....contrary to looking halfway decent. I also find the reflection to be distracting in an environment that requires constant vigilance.

I ordered Trivex Transitions Vantage, with the Anti-Reflective and Anti-Scratch. But what would you recommend to someone deployed in a bright and hostile environment?

I also find myself getting headaches at the computer, something I currently believe is caused by the excessive lights and monitor brightness. When I put on the military sunglasses, I feel like a pressure is taken away.

My military glasses are as follows, one pair normal, one pair 15% grey tint. Plastic Lens. (really thick)

R.E. -4.50 Sphere, -0.75 Cylinder, 080 Axis, Prism 5, BO
L.E. -5-25 Sphere, -0.25 Cylinder, 100 Axis, Prism 5, BO

I miss wearing contacts, and they wont do surgery out here due to risk of infection. So what are your recommendations?

V/R,
Bill
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Cactus Jack

Posts: 100

Joined: Sat Sep 24, 2011 3:00 pm

Post Mon Oct 21, 2013 4:15 pm

Re: prisms

Bill,

Most Eye Care Professionals (ECPs) will under prescribe prism. There are a couple of reasons for this. BO prism corrects for the eyes trying to over converge, but it can also cause the eyes to converge. Reading causes the eyes to converge even more. The eye muscles and their positioning system can get used to the extra convergence and that position can become a new relaxed place, which can ultimately limit the eye's total motility range.

I am not familiar with the glasses and frames you purchased, but it is possible that the transition is not enough in bright sunlight to provide adequate protection in your environment.

Two things are going on when you use the computer.

1. You are looking into a light source.

2. Your eyes are converging when you use the computer. The actual amount of convergence depends on working distance, but I would estimate that it is about an additional 8 to 10 total diopters (4 to 5 in each eye).

It is possible that you have developed some sensitivity to light and because UV light causes the transition to occur and computer displays do not emit UV light. Also, when wearing the new glasses with 5/5 BO the additional 4/4 or 5/5 is causing problems, but frankly that would surprise me if that is the problem. Normal visual activity (e.g. reading small print) causes more convergence than that. Are you getting headaches when you read?

Cactus

I think you should report the photosensitivity with your military medical personnel. Photosensitivity is one of the symptoms manifest by several different diseases.
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duncanw

Posts: 2

Joined: Sun Oct 20, 2013 1:53 pm

Post Tue Oct 22, 2013 11:34 am

Re: prisms

Thanks for the input.

My transitions aren't here yet, i'm still using the military issued aviators.

I have had light sensitivity for years now and seem to get headaches when using the computer, a tablet, ect.
I lower the brightness in an attempt to compensate, but this only helps a little.

My office has bright florescent lights right above me and two computer monitors in front of me, so I am tempted to get a new set of glasses made with a 10% tent for office use.
The question with that is which color tint will work best for indoors?

A military eye doctor once recommended that I wear sunglasses whenever possible because my eyes were likely sensitive to sunlight.
I have blue eyes, but besides that I am unsure why she had this opinion. The military doesn't really believe in anything besides the most basic of glasses.

So, currently I have two sets while I await for my transitions to arrive.
1. Gold Framed Aviators (not cool ones regretfully), with plastic lenses.
2. Same as above but with N-15 (15% grey) tint.

I am leaning towards buying another set of glasses with a 10% blue tint, as some of the computer glasses out there seem to be blue or yellow in nature.

I have noticed that when I stare at something really small, there is an almost pressure feeling like I am working against the natural position of my eyes.

Sadly, my options to see a doctor out here are non-existent. So anything beyond what I can figure out or adjust myself is going to have to wait until I get home.

Thanks again,
Bill
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Cactus Jack

Posts: 100

Joined: Sat Sep 24, 2011 3:00 pm

Post Tue Oct 22, 2013 2:19 pm

Re: prisms

Bill,

I don't know if this would be possible for you, but I would suggest ordering some inexpensive glasses from an on line retailer such as Zenni Optical. This is purely an experiment to see if it helps so try to keep the cost as low as possible. Zenni has single vision glasses for as low as $6.95 (depends on frame) plus shipping, but you need some extra cost options.

1. Reduce the sphere correction to reduce the accommodation required to focus at the working distance of the displays. I suggest starting with a reduction of 1.00 diopter in sphere. Accommodation effort can affect your over convergence response.
2. Consider eliminating or reducing the BO prism for this experiment. Your working distance is probably 20 - 24 inches which may provide all the convergence you need. I can give you a simple test for estimating your relaxed convergence if you want to try, but lets don't introduce experimenting with prism until you try this and see if it makes any difference.
3. I would consider yellow, amber, or gray tint. I would not use blue as a first try. Typically colors near the middle of the spectrum are the most comfortable. Gray has a lot of merit because it does not distort colors, if that is important. Color displays use Red, Green and Blue to create White and most other colors in the visible spectrum by varying the amount of each primary color. Yellow and amber are a combination of Red and Green, the actual shade depends on the mix.

Suggested Trial Computer Glasses Rx:

R.E. -3.50 Sphere, -0.75 Cylinder, 080 Axis
L.E. -4.25 Sphere, -0.25 Cylinder, 100 Axis

I would consider 50% tint
Reduce the distance PD by 3 mm for the closer working distance.

With the tint and shipping to an APO, the total cost may be under $20.

Hope this helps. Please let me know if you have more questions and what you decide to do.

Cactus
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Brian

Posts: 27

Joined: Thu Nov 10, 2011 6:12 pm

Post Thu Nov 14, 2013 12:23 am

Re: prisms

Has anyone ordered glasses with prisms from Zenni yet? I know they just started carrying them.. Currently they offer up to 5D of prism in each eye and that is what I am at now 5BI in each eye. I was thinking of ordering a pair as a backup from there and was just wondering if anyone had any luck in the past.
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Cactus Jack

Posts: 100

Joined: Sat Sep 24, 2011 3:00 pm

Post Sat Nov 16, 2013 7:12 pm

Simple Prism Test

I have had several requests for the following test for prism correction.

It is not hard to measure the amount of prism it would take for full correction. All it takes is some adding machine or cash register tape, a marking pen, some painters or masking tape (ideally with very weak "stick-um" for easy removal) and something to measure distances.

It is a little easier to work with metric measurements, but you can do it also with inches and feet. You just have to do a little more math for conversions between the two.

This test is based on the definition of 1 prism diopter as: "That amount of prism that will deflect a ray of light 1 cm at a distance of 1 meter (100 cm)".

Ideally, this test is done without any prism correction in your glasses, but you need to be able to see some calibration marks on the adding machine tape with reasonable clarity. If you can't see the marks without glasses, you can still do the test, but you must account for the prism in the glasses.

1. Select a fairly blank wall that you can attach the calibrated adding machine tape to, using the painters or masking tape.

2. Decide where you will stand or sit while doing the test. Between 3 and 4 meters or 10 and 14 feet works best. Measure the distance from that location to the wall selected in Step 1.

3. Calculate how much displacement 1 prism diopter represents at the distance measured in Step 2.

4. Using the marker, mark the adding machine tape with major divisions 5x the distance calculated in Step 3 and optional minor tick marks at 1 prism diopter intervals. The marks need to be big enough to see easily from the distance in Step 2. You might want to identify the major divisions as 0, 5, 10 etc. Note: Some large bold markers will bleed through the adding machine tape and permanently mark the surface you are using as temporary backing for the adding machine tape. Test and take appropriate precautions to prevent damage by the marker ink.

5. Attach the adding machine tape, stretched out horizontally, to the wall selected in Step 1.

6. On another short piece of adding machine tape mark an arrow lengthwise and attach that piece of tape to the wall, vertically, so the arrow is pointing at 0.
You are ready to do the test.

7 Place yourself at the location selected in Step 2, let your eyes relax so you see double and note where the "0" arrow appears to point in the displaced image. Try this test several times during the day and at varying degrees of fatigue. Make a note of your results.

8. If you are wearing glasses with prism, adjust the readings in Step 7 for the total prism in the glasses.

This test will work with horizontal prism (Base Out or Base In) or vertical prism (Base Up or Base Down) by the placement of the long tape and short tape. Often both horizontal and vertical prism exist at the same time.

Note: It is sometimes difficult, if small amounts of prism are involved, to tell if the prism correction needs to be Base Out or In, Up or Down. You may be able to tell by noticing which way the images are displaced when you block the eyes alternately. For example, if you cover the right eye and the image from the left eye is on the left, you probably need more Base Out.

Please Let me know if you have any questions and if this works for you.
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Brian

Posts: 27

Joined: Thu Nov 10, 2011 6:12 pm

Post Wed Sep 10, 2014 6:57 pm

Re: prisms

Just wanted to check in and see how everyone on this board has been making out with their current prism correction. This year for the 1st time since I got prisms in 2010, my prism stayed steady at 5D BI in each eye, so hopefully it has leveled out.. My 1st correction was 2BI in each eye in 2010, went to 3BI in 2011, 4BI in 2012 and 5BI in 2013, so the fact that it is stabalizing and that I am having very little double vision with my current script is a good sign for the future.
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traumaemt

Posts: 72

Joined: Wed Jan 09, 2013 2:58 pm

Location: U.S.A.

Post Thu Sep 11, 2014 7:53 am

Re: prisms

Brian

My double prisms are working just fine for me. It is kind of hard to see without them, but I can manage for a short time. I have no double vision at all with them, for the most part. My biggest problem is the fact that I have Multiple Sclerosis, and my eyes can change at any time. I have went through periods where my eyesight is fine with my glasses, then hurt with them, so I take them off, and I am fine without them. This can last anywhere from days to months. Then go back to wearing them, then go to where they are not strong enough for days to months, to complete blindness in one or both eyes. So my eyesight really does run the whole gamut of the range.

My current script is:

OD Pl -0.50x107 4BI 1BU Add +1.25
OS -0.25 4BU 1BD Add +1.25

Progressive lenses. (I cannot remember what the intermediate power is for the progressive lenses).

I hope that helps you, and is what information you were looking for.

Traumaemt
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ikchyadhari

Posts: 1

Joined: Fri Sep 19, 2014 6:53 am

Post Fri Sep 19, 2014 6:59 am

Re: prisms

Hi I am 27 and I am suffering from having double vision every now and then. Its not permanent. It happens when I usually sit in front of computer for too long. When I went to the optometrist he prescribed me 6 BO in each eye with + 0.75 in my right eye. I have far sightedness. What I want to know is do somebody like me who dont have permanent double vision needs a prism correction? and other thing that I want to know is, if I start wearing prescribed prism lens will I be dependent on it on the long run?
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Brian

Posts: 27

Joined: Thu Nov 10, 2011 6:12 pm

Post Fri Sep 19, 2014 8:14 pm

Re: prisms

6 BO in each eye is a lot of prism to start out with. When I first got a prism correction, they started me at 2 BI in each eye and even now, 4/5 years later Ive stabalized at 5BI in each eye. I didn't experience double vision all the time either when I first got prism in my glasses, but the prism completely relaxed my eyes. You could try to start using the prism/reading correction for just up close activities, but I think you will find, with your prescription strength, once you start wearing glasses, you will want to wear the glasses all the time and they should help your vision tremendously and completely cut out your double vision.. Have you ordered the glasses yet? Let us know what you think after you receive them.
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Cactus Jack

Posts: 100

Joined: Sat Sep 24, 2011 3:00 pm

Post Fri Sep 19, 2014 9:32 pm

Re: prisms

ikchyadhari,

Base Out (BO) and Base In (BI) prism are similar, in that both types of prism bend light rays. However, the big difference is the direction they bend the light rays and why they are used.
There is no reason for the eyes to need to diverge beyond having the axes of vision be parallel for viewing distant objects. If the eyes do diverge, BI prism is used to bend the light rays toward the nose and fuse the images.

Base Out (BO) prism is used to bend light rays away from the nose and is used for several reasons. It is normal for the eyes to turn inward (converge) for close focusing. If they did not, ou would see double whenever you tried to look at something close. The three most common causes for needing BO prism are Muscle Imbalance, Cranial Nerve problems, or Eye Positioning Control Issues in the Brain. Lets tackle the Brain Issue first. There are two interconnected eye muscle control system in the brain. One system controls the ciliary muscles and the accommodation power of the crystalline lenses in your eye. The other controls the 6 muscle pairs (3 on each eye) that control the position of your two eyes.

The eye positioning system appears, from an engineering point of view, to be what is called an "Open Loop Servo" system. There are two basic types of servo positioning system. One is a "Closed Loop Servo System" where the control system knows EXACTLY where the CONTROLLED element of the system os located or pointing. These types of systems are used for precision machining where the position of the tools are known within a tiny fraction of an inch or mm. To my knowledge, there are no Closed Loop Servo Systems in the human body. However, the body is loaded with Open Loop Servo Systems where the eyes play an important role. Open Loop Servo Systems use the eyes to look at the results of movement. When you reach for an object, you almost always have to look at your hand position to be able to make nearly instantaneous position corrections. The eye positioning system uses the two images from your eyes to control the position of your eyes.

To make understanding how the system works a bit more difficult to understand, there also seems to be a two-way connection between he eye focus control system and the eye positioning system that causes the eyes to automatically converge when you try to focus close. The strength of this connection varies with individuals and is sometimes the cause of over convergence in Hyperopes (people who are far sighted) because the act of using your internal focus mechanism (accommodation) to correct your distance vision and work harder than normal to focus close, also causes the eyes to converge or cross. You can also have muscle imbalance or cranial nerve issues where the eyes want to turn inward or cross and the interconnection will sometimes cause the eyes tot try to focus close, it seems to work both ways.

The problem you and everyone else who experiences Double Vision has is that no matter what the cause, there are only three solutions. Glasses with prism correction, muscle surgery, or sometimes vision training. At some point, you will probably need to see a Pediatric Ophthalmologist (they also work with adults) who specialize in problems of this nature. However, before you do that, I would like to suggest that you do the "Simple Prism Test" described a few posts below, that I devised and posted nearly a year ago.

I need to make a few changes to the test to clarify the conditions, but I can tell you here. You need to post the calibrated strip at least 10 feet (3 meters) away so your eyes will be pretty relaxed and not inclined to converge too much because of the closeness and you need to try to let your eyes be as relaxed as possible. You may be surprised at the numbers you get, but you need to try the test when you first get up and then when you are tired. Most ECPs are trained to significantly under prescribe prism - perhaps only a 50% correction, which is not necessarily a bad thing, but it can be very annoying if your eyes break fusion too often.

You asked a question about how much priam will you ultimately need, the answer is no one really knows at this time, but it can become very significant depending on the cause. Also, you need to know that muscle surgery is not always as effective in adults as it is in young children. One thing that could be affecting an over convergence tendency is that you actually have significantly more Hyperopia than was revealed in your exam. The condition is know as Latent Hyperopia.. That is where your ciliary muscles and crystalline lenses have become so used to correcting your Hyperopia that they have trouble relaxing. The solution is to wear PLUS glasses so your eyes can gradually relax and they can eliminate the over-convergence tendency.

I urge you to perform the Simple Prism Test and get back to us with the results and we can go from there. If you don't understand anything or have any questions, please ask for clarification.

May I ask your occupation and where you live?

Sorry to be so long winded, but this is a complex subject.

Cactus
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