Optometrists in Fort Collins Usually Prescribe Prism Eyeglasses For Double Vision
Has your eye doctor prescribed prism eyeglasses for you or your child in a new eyeglass prescription? It could be due to crossed eyes, lazy eye, or some diseases of the eyes or body.
Prisms are thin pieces of the optical material that is used in prescription eyeglasses. You may remember them from high school physics. They have a base that is thicker and an apex that is thinner. Due to the light bending properties of the lens material, the thicker lens base slows light down as it passes through. Since the prism is thicker at the bottom base it slows light down longer than the top apex, and light changes direction down towards the base as it exits the prism. If the lens were equally thick throughout, it would slow the light down but the direction would remain unchanged. The amount of direction change is determined by the index of refraction of the material compared to the index of refraction of air. Lenses with higher indexes of refraction allow optometrists to make the ultra thin lenses that have drastically improved eye comfort and cosmetic appearances in recent years. The light bending capacity of a lens material is referred to as the index of refraction. The value in space in a vacuum is 1.0, essentially the same as in the earth’s atmosphere which is 1.0003. Eye glass lenses now have indexes of refraction from 1.5 to 1.7, with the higher numbers being the thinnest.
Eyes that cross can turn in or out, and also one eye can turn up or down. Strabismus is the technical term for a turned eye. Eyes that turn out are referred to as exotropic while eyes that turn in are called esotropic. An eye that turns up is hypotropic and one that turns down is hypotropic. These are all considered as cases of strabismus, or eyes that actually do cross. Often they are mistakenly called “Lazy Eyes.” A lazy eye is a different condition but it may result in a crossed eye. A combination of eyes turning laterally and vertically is common. When this results in double vision, it can be completely disruptive to mobility and lifestyle of the affected person. If the eye turns are present at birth, there may be no double vision present. The brain has the capacity to suppress or turn off the area of vision that results in the eyes perceiving double at early ages. When a person sees double, prisms, eye exercises known as vision therapy, and surgery are the three options eye doctors have to try and restore normal visual functioning. Prisms do not appear as a strange looking triangle in the lens. They usually show up as thicker and thinner edges on the eyeglass lenses. Normally they are ground into the shape of the lenses, but because of optical properties, some lenses can have the optical center repositioned to induce prism. There can be an adjustment to prism added to a prescription while the brain relearns how to interpret the eyes seeing single. When diseases such as strokes and diabetes cause double vision there can be some fluctuation over time, and frequent eyeglass prescriptions changes to adjust the amount of prism may be required. Temporary press on prisms known as Fresnel lenses may be used in some cases when change is expected but their optical quality tends to be very poor.
Your eye doctor may prescribe prism in your eyeglasses for other reasons
Some people will only have a tendency for an eye to turn, and while it may not actually turn it will result in eyestrain, fatigue with reading, headaches from using your eyes, and other symptoms. These are referred to as heterophorias instead of strabismus. Instead of exotropia your optometrist would call it exophoria. Any term ending in phoria means a tendency to turn while tropia indicates an eye that is turned. To complicate matters, sometimes eyes will cross at one distance and not another, or when viewing in only certain fields of gaze. In cases of traumatic head injuries yoked prisms may be used to help retrain a disrupted visual system by altering spatial perception.
Some serious health problems can cause double vision, and any new onset or increasing condition of double vision should be thoroughly examined by your optometrist
When double vision occurs after the age of fifty, common causes are thyroid conditions, high blood pressure and diabetes. Try to notice when it occurs and what makes it worse to help your optometrist in treating your eye condition with the best methods possible. In the case of a brain tumor inducing double vision, a trip to the eye doctor could save your life.
Hi Brendan,
The amount of prism that can be ground into a lens is determined by the frame size, shape, and the amount of prescription in the lenses. Too much prism will not allow the lens to stay in the frame, and the distortion induced by the prism may become excessive. That being said, 5-6 in each eye is probably the upper limit of what is practical. Fresnel press on prism can extend this range but they do significantly reduce the clarity of vision. People that are partially sighted can tolerate higher amounts of prism in specially ground lenses since the distortion of vision form the prism will not be as noticeable. Hope that helps.
Best Wishes
Hi Melissa,
Normally with prism being used Base Out it would be used in front of each eye. Are you sure there is not some vertical prism base up or base down in the glasses? If it is just in front of one eye I would think you should be fine without it at those times but you would need to ask your eye doc for an Rx without it.
Best Wishes
Thanks for your reply, that all makes sense. When you talk about vision therapy, could that be the same type of exercises I used to do when I was undergoing vestibular rehab therapy? I would toss objects and follow them with my eyes, read a chart that had letters all over the place, and turn my head back and forth while keeping my eyes focused on an object in front of me. Sound familiar? If those are what you’re talking about, I can go back to doing those exercises at home, or get my ENT to prescribe more formal VRT. If those aren’t what you meant by vision therapy, would you please explain what this is and how I could get some?
Thank you again. I’m glad I found this site. (Funny detail: I lived in Colorado for eight years but am now back on the East Coast.)
Hi Peggy,
That is pretty close to what I mean. One of the things that I feel is important is adding motion to the activities. By that I mean after tracking objects you track with your head in motions like you described, then move on to tracking and focusing with your body in motion, then adding the challenge of varying postural balancing while doing the above. Beyond that other perceptual strains (like noise and mental processes like math) are added to overload the system. When you can deal with high levels of sensory input and function well you can usually overcome the symptoms. You may see it referred to as visually-related motion sickness, See Sick Syndrome(SSS), or Neuro-Ocular-Vestibular Dysfunction and a few other names.
Best Wishes!
Hi Liesal,
You are still pretty early in the process so give it some more time to improve. I would try the prisms knowing it could still change over time. Second opinions are always a good idea but it will probably take a little while to get an appointment. If things get better in the meantime you can always cancel the appointment.
Best Wishes
Hi cc,
With vertical prism there is not normally adaptation over time so its not much of a concern. Some other types of prism may have adaptation and prove less effective as it is worn. Vertical eye turns usually require smaller amounts of prism. You might notice double;e vision more frequently when you don’t wear the prism but that is usually moire awareness and not more reliance on their prism.
Best Wishes
This is great… I really think I might be on the right track for something that could help me now.
Could you tell me what kind of specialist I should be looking for to help me with this? Am I looking for an ophthalmologist who specializes in this, or a neurologist, or a physical therapist? Where can I start looking for an expert to guide me through this? I’m on the East Coast, so unfortunately I can’t come in to your office.
Thank you so much for the new clues. I think pursuing this could really help me improve my balance beyond where I am now.
I’m wondering, is any downside to prism eyeglasses? I sometimes see double when looking at faraway objects, but not always. My optometrist gave me an eyeglass prescription with a new prism component, which fixed the problem (at least, when looking at the eye chart). But if I get new glasses with the prism component, will my eye muscles get complacent and weaker? Or will my eye muscles be healthier, or no effect?
Hi F.D.,
There was a saying when I was in school that went something like this “Base In is a Sin, Base Out without a doubt. Base out prism is used for eyes that turn out (exotropia) ans base in for eyes that turn in (esotropia). There is not a problem when it is used either way. For eyes that have a tendency to turn out or only turn occasionally there can be adaptation to the prism requiring increasing amounts over time. It is not permanent, if you quit wearing the prism it will normally return to its former state. It’s a “sin” to use the prism in many cases like this because it does not do any good over the long term. The eye muscles are about 100x stronger than required to maintain eye alignment. Prisms have no effect one way or the other on their strength or health. Eyes turn due to inadequate nerve impulses, faulty insertions or faulty tendons. When all is said and done, prisms are worth trying in most cases of eye turns but they may not always work.
Best Wishes
Hi Sir,
i am an optometrist from India,now i have a case where a patient of mine is having congenital nystagmus ,his rx consist of OD: -2.75/-1.75 X 10 OS: -0.75/-3.0 X 175 , now the problem is that he has null position in the dextroversion and needs to do bit chin down in order to dampen and to read with proper clarity in both distance and near, Can you suugest what should be done in this as i have found prism of 13 bi in OD @ 30 and 10 BO@160 so as to bring his null postion in primary gaze,therefore kindly suggest or advice as what next should be done…… .the patient is wearing contact lenses in both the eyes and is aged 22 yrs.
looking forward for your valuable suggestion…
regards,
karan raval
I’ve had brain surgery about 6months ago and as a result I am suffering from double vision. I had prism glasses made to correct it. I have two questions a) do contact lenses exist for such a problem b) are there any exercises I can do to help reduce or eliminate the problem of double vision please? Thanks for your help
Hi Anna,
Some contact lenses with certain type of prescriptions can incorporate small amounts of vertical prism but not horizontal. It usually is not enough to resolve issues like yours, but in the right cases can help a little. Vision therapy type of eye exercises can help many cases. Prism in glasses is the easiest and least time consuming approach. There can be other benefits from vision therapy for patients who have had head injuries or brain surgery. You might want to talk to an optometrist in your area who does neuro-optometric rehabilitation.
Best Wishes
Hi Karan,
A lot of people seem to be having success with mini scleral rigid gas permeable contact lenses in dampening congenital nystagmus. I have only tried it with one patient so far using a 16.5mm diameter lens.
It seems to work very well in some patients. I hope that is some help if you have not tried it yey.
Best Wishes
I am having problems with pain on one side of my head. My doctors are currently looking into this, but I saw my optometrist today and he told me to make sure my doctor knows that I have Prism glasses, that it may be relevant. He was very busy so I could not talk to him. What did he mean? Do you know? What should I be telling my doctors about?
Thanks.
Mike
Hi Michael,
One sided pain is always a worry. You eye doctor must have found an imbalance in how your eyes were working together. Prism can help neutralize that imbalance and relieve stress in the visual system. If that does not help there are a number of other conditions that can create pain on one side of the head. Temporal arteritis tends to cause head pain, scalp tenderness, and pain when chewing. Blood tests can detect this a similar diseases. Tumors in the brain can be detected by imaging with MRI’s. Migraines headaches are also common although they usually are not localized to one side all of the time. Prism in glasses are a very inexpensive way to rule out eye muscle imbalances as the cause (compared to most other forms of testing). If you don’t get quick resolution ask for a referral to see a neuroloigist.
Best Wishes
Also- keep a record of when they occur, where they are, how long they last, if anything makes them better or worse, is it only during the week or on the weekend also. Any other symptoms that may also be occurring. It also can help to know how bad they are on a scale od one to ten. Keep a log and discuss it with your doctor. After you get the new glasses you will quickly be able to tell if they are helping.
i started to have blurred vision/double vision tuesday last week . tests have been done and a muscle ombalance have been found. i have been using a pair of prescribed glasses with a prism in the left lens. i need to get back to work soon but although i can adjust to the glasses sitting down , when i move my head or walk about i start to feel nausious and i cant see this improving . do you think this will improve if i persevier please ?
Hi Malcolm,
Do you know the cause of the muscle imbalance? While a primary cause is not always found it does have bearing on how well you will adapt over time. In most cases the symptoms you are describing will decrease and you will adapt to the prism. If there is an underlying systemic problem like thyroid disease the muscle imbalance could change over time making adaptation more difficult. The majority of people never show a specific cause and adaptation occurs over several weeks to several months.
Best Wishes
I am looking for a glaucoma glasses to allow a cousin of mine to play football or others sports.
As he lost the peripheriferal vision its very difficult for him to play some sports.
If tyou don’t have the right glasses could you inform were can I find it?
Would be necessary a doctor prescription to find the correct glasses?
thank you
Hi Lucercio,
The first question is does he have a loss of peripheral vision that encircles a central zone, or is it a loss of one side in each eye.
For circular losses he can uses lenses that have a vertical strip of prism placed toward the out side edge of each lens. Then when you look to a side one eye will have expansion of the field of vision while the other will still be viewing through a normal part of the lens. This can work fairly well if the vision field covers about 100+ degrees. For larger areas of peripheral vision loss he may need to use a tubular type of field expansion system. This entails either surrounding a normal central area with prisms that are focused in different directions so the field can be expanded not only to the sides but also up or down. Small round segment areas can also be added to the side of each lens. When these are viewed through they serve to minify what is seen. Since things are smaller they also have a larger field of view and expand peripheral vision.
For vision losses to the side there are two systems that are frequently used, The Goettlib System and the Peli system. For people who have lost vision from strokes or certain types of head/eye injuries these can expand (and sometimes help treat) losses of side vision.
Many of these type of systems can be tried with inexpensive Fresnel prism that adhere to the lens and can be removed. The optics are not usually good enough for permanent use, but they help let you know how they work, and if that is something you want to pursue.
All of these systems are rather costly and you are better off taking him to a specialist in low vision or neuro-optometric rehabilitation. It takes some knowledge to find the right solution for the right patient. There are frequently low vision centers in larger cities that may have resources if cost is a concern. He is lucky to have you helping him.
Best Wishes