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Acuity and Prescription II

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Cactus Jack 24 May 2018, 09:35


I would suggest ordering the least expensive frames you can, to make sure she likes them and they are comfortable. If you are considering ordering from Zenni, you might consider their least expensive Anti-Reflective coating.


Cactus Jack 24 May 2018, 09:31


For near (reading glasses), reduce the PD by 3 mm. The PD should also be reduced by 0.3 mm per BO prism diopter or another 2 mm (0.3 x 6 = 1.8 mm). The online retailer may automatically reduce the PD for the BO prism.


Jhon 24 May 2018, 00:18

Hi C

We have only got the distance PD its 63

Thanks for your help

Cactus Jack 23 May 2018, 23:12


Oops, it should be:

R +2.50 -1.00 130 Prism out 3

L. +2.50 -1.00 90. Prisim out 3

I missed the - in front of the +2.50 for the right eye.


Cactus jack 23 May 2018, 23:09


R -+2.50 -1.00 130 Prism out 3

L. +2.50 -1.00 90. Prisim out 3

Do you know your wife's PD?

It may be shown as what appears to be a fraction such as 62/59. The first number is the distance PD and the 2nd number is the near PD.

If you do not have the PD, it is easy to measure. We will tell you how and how to adjust it for near and the Prism.


Jhon 23 May 2018, 14:20

My wife has a new prescription

R -1.00 -1.00 130 add 3.50 Prisim out 3

L. - 1.00 -1.00 90. add 3.50 Prisim out 3

She want to order a pair of reading glasses on line what would her prescription be

Many thanks

Kris 19 May 2018, 11:43

Hi Cactus,

Iím sure my strabismus is a result of muscle imbalance. I was originally treated as a young child with glasses (stopped wearing them when I was 7) and surgery and was fine until my late 30s. I always assumed everyone could see double if they relaxed their eyes, but turns out thatís not the case. Iíve discussed the possibility of another surgery with my ECP, but heís not sure how effective it will be and since Iím well managed with prism, thinks that we can hold off.

I did wonder about dry eyes when the ghosting got worse, but eye drops had no effect when I tried them. Iíve never felt that my right eye acuity was as good as it could be, but it was definitely worse than ever at this eye exam. Where I could read a line, even if it was blurry before I couldnít make it out at all this time around. On the near testing I could make out the 20/60 line with some effort, whereas I could read the 20/25 line with my left eye without problem. I donít know why my right eye acuity has gone down the way it has, but Iím sure age has something to do with it. The good thing is that it could be corrected.

My ECP has monitored me pretty closely for cataracts as he thought he saw something on my original exam, but there hasnít been any change in 9 years, so cataracts arenít a cause of my issue (at least not yet).

Cactus Jack 19 May 2018, 08:45


There is no way to predict how much prism you will ultimately need to keep from seeing double. Within limits, your EPCS can mask your actual need for prism correction. It is very similar to the Focus Control System masking the actual need for Plus glasses in Hyperopia. That can be partially revealed by dilation, but if a person has developed significant Latent Hyperopia over many years, it can take a long time for your Ciliary Muscles to fully relax.

There are 3 possible sources of Strabismus, the general medical term for the eyes not pointing in the same direction. There could be a problem in the EPCS itself as a result of a blow to the head, excess imbibing of alcohol, or a malignancy. Another possibility is something affecting the Cranial Nerves that carry the signals from the EPCS to the 12 muscles attached to the eyeballs. Or lastly, Muscle Imbalance, where one of the muscle pairs is weaker than the other. This last one is the "catch all" diagnosis because it is really the only one that can be pretty easily fixed (maybe) with muscle surgery, therapy, or prism correction. The nice thing about prism is it is like any other form of external vision correction. The amount of correction can be changed by the patient by simply putting on or taking off their glasses or by their ECP.

There can be other things that cause "ghosting" of images including variable Astigmatism related to a dry eye condition and unusual forms of Cataract just to mention two. Your EPCS works best when it has very sharp images to work with.

As I mentioned before, you seem to have an ECP that is willing to listen and work with your to provide the best vision with the least prism. That is a good thing. Just be sure and be open with your ECP. There is nothing to be gained by not telling the whole story..


Kris 18 May 2018, 23:50


I did the test with my current prescription of 4.25 BO in each eye. Does that mean I could potentially end up with almost 10 BO each eye, or is it possible that I could settle with less than that? I donít really experience double vision now (maybe a little when Iím tired, but not like before). I know that the eyes can demand more prism so you have to be cautious with increasing. I thought Iíd read that people with strabismus will hit a point where they are at full prescription and donít need more, but I could be wrong.

I havenít done the prism test in lenses without prism in awhile, but I think images could be as far apart as 120cm (give or take 10 cm) at 3 meters wearing my distance correction but no prism. Following what youíve said, this could translate to me potentially needing up to 20 BO prism correction (split 10 per lens). This seems like a lot. Is it? Could it go even higher, or am I likely to settle there?

Iím not sure how the changes in vision in my right eye may be affecting my double vision, but I am curious to see how much more comfortable I will find the new lenses. RIght now, the ghosting Iím seeing is the most problematic issue.

Cactus Jack 18 May 2018, 22:45


57 cm at 3 meters is about 19 diopters total. Typically, ECPs like to fit about 1/2 the measured prism and would split the total between your eyes,

Hmmm, 19/2 = ~10 diopters. Split between your two eyes = 5 BO in each eye. That is not a hard and fast rule and sometimes they will go a bit higher if you are having double vision problems with the 5 BO in each eye.

Vertical prism is treated separately and is often a bit more fully corrected using BU in one eye and BD in the other because there is not much need for the eyes to move in different vertical directions. Horizontal eye motion requires for the eye to converge and diverge and focal distance changes, but there is never a requirement for the eyes to diverge beyond parallel. It is also necessary for the eyes to be able to track together when looking left and right at different amounts of convergence depending on the distance to that is being tracked.

The EPCS is a truly amazing system. However, your vision system and EPCS system are not nearly as clever as the lizard that has the ability to look in two different directions at once.


Kris 18 May 2018, 20:15

Thanks Cactus,

Iíve done your prism test before and saw your recommendations for preparing for an eye exam. I have to say that at this exam things were much easier (in previous exams it felt like I was choosing between degrees of blurriness, whereas with this exam there was clearly a clear and a blurry option). My ECP tells me that Iím very sensitive to small changes in prescription and has replaced lenses before for me when the prescription wasnít quite right.

Iíve tried the prism test with my current glasses and at 3 meters there was about 57cm between images, although I could fuse easily after letting things go double.

I agree about having a good ECP. Heís been good at working to get the right prescription for me. Iíve had many people tell me to save my money and go elsewhere (large box store, not to be named) to get cheaper lenses, but I just donít feel Iíd get the same service.

Cactus Jack 18 May 2018, 15:34


Have you read my "How to Study for an Eye Exam"? There is a section about how to "fine tune" the Cylinder Axis.

Typically Astigmatism is very slow to change, but the part of the the exam that determines Cylinder and Axis is VERY subjective because the usually method requires that the patient judge relative blurriness. That is difficult even for a person who has had many eye exams.

You have to ask the ECP if you can fine tune the axis angle at the appropriate place in the exam. Most ECPs appreciate your active participation in the exam.

It sounds like your ECP is a "keeper".

If you are unable to locate "How to Study . . . ", I will post it again. Also, you might find the Simple Prism Test useful, if you would like to try it.


Kris 18 May 2018, 14:17

I finally had an eye exam and told my ECP about my issues with ghosting and eyestrain. It turns out I didnít know my old eye prescription. It was L +1 4.25 BO and R +1.5, -0.5 4.25 BO with a 2.25 ADD.

At my exam, my ECP did say I had an increase in astigmatism and he seemed mildly surprised, but said some people do increase with age (Iím 47). Also, he detected some vertical eye deviation which has never been a problem before. It was relatively small, I think he said 1 prism (not sure if it was up or down, the second image was below the first). He thought this deviation may just be that my right eye is moving around trying to better fuse images and may resolve with improved correction. In the end, he said he could correct the vertical deviation, but thought it would be better to correct the astigmatism first and see if the issue settled. He did decide to go up in the horizontal prism (something about this may balance out the vertical deviation- I think he thought if the eyes werenít struggling to maintain fusion, I may not have the vertical deviation).

My new script is L 1.00 -0.25 cyl 5 BO and R +2.00 -1.25 cyl 5 BO with 2.25 add. Iíve always felt like my right eye was under corrected and the image was so much clearer than itís been. I am a little surprised at the difference from my old to new astigmatism correction though but I believe itís still a fairly low correction. My ECP did think I may need tweaking of the prescription and said I may need to come back in for adjustments.

Should I expect further worsening of my astigmatism, or is it that Iím just being properly corrected now? Iím hoping the new lenses come in quickly as I would like to resolve the eyestrain symptoms Iím having.

 16 Apr 2018, 16:12

Fuck off likelenses.

 16 Apr 2018, 16:10


"The diagnosis was binocular dysfunction". Along with many other dysfunctions.

Lou 16 Apr 2018, 15:51

Hi Kris

I can only talk from personal experience, but in my case, a small amount of uncorrected astigmatism is enough to cause pretty bad eye strain, hence why I wear a very small astigmatism only prescription full time.

I have convergence insufficiency. It is a lot better than it was before eye exercises with the help of an orthoptist, but is still present enough for opticians to comment about it, and suggest that I start eye exercises again. Personally, I don't yet feel the need to go down this path again, so haven't done eye exercises since 2010.

I have previously had a small amount of prism, but don't personally like it, and feel that it encourages me to focus on rain spots on the car windscreen when driving, probably owing to the prism mimicking convergence which obviously occurs as you focus more closely.

I suppose that it would probably work better for me if I had a separate reading prescription, but I don't, and I didn't like driving with prism.

I personally don't experience eye strain from not wearing prism.

Obviously however we are all different, and even though uncorrected astigmatism bothers me a lot more than uncorrected convergence insufficiency, someone else may find the reverse, and obviously it depends on the amount a person has of each.

I hope that this will help.

Best wishes


Weirdeyes 16 Apr 2018, 15:00

Just returned from my vision therapy assessment. The autorefractor has some interesting results. With my contacts which are R +0.75 -0.75 L +4.50 -1.25 the autorefractor said Iím R +0.50 -0.37 L +0.12 -0.37. A while ago my autorefractor results without contacts was pretty much the same in my right eye. So my eyes are relaxing, but not enough for any significant change. As expected the doctor didnít even mention the autorefractor results, but to me itís a bit of progress in the right direction. The diagnosis was binocular dysfunction. He said that could account for some of the lack of detail I see. He also prescribed some weak plano prism glasses with 0.50 base in for each eye to wear over my contacts. Thatís weaker than the prism Iím wearing right now, but he says less is sometimes more. He also said Iíll get better visual function from contacts. Iíve never tried contacts and prism before, so this could be good. But I guess the therapy more important than any prescription. I also scored perfectly on the depth perception test and heís not worried about the vision in my left eye. Iím pretty happy with that. Iím glad heís aware that amblyopia isnít my problem. A few people in the past have fixated on my left eye being half a line worse than my right eye.

Kris 16 Apr 2018, 13:38

Thanks Lou and Cactus Jack. It looks like I will need to book an eye exam soon. I will keep your tips in mind and will definitely mention the findings with the astigmatism screening test I tried. Can uncorrected astigmatism be enough to account for the eyestrain Iím experiencing, or is it likely that I will need othe adjustments as well? Given that at my last eye exam it was found that I could use an increase in my prism script, I guess I shouldnít be surprised if that happens as well. Iím noticing ghosting on my computer screen as well as when i watch TV. Before when I noticed it, it was only noticeable at distance. I will post once Ive had an eye exam.

Lou 16 Apr 2018, 04:40

Sorry, in my previous post when I said:

Obviously I can't do anything about SPHERE values being determined in 0.25 steps, even if I can determine 0.125 difference in cylinder, but I am going to ask about my left eye axis values next time and see if I can fine tune them like Cactus Jack suggests.

I meant to say CYLINDER rather than SPHERE values.

All the best


Lou 16 Apr 2018, 04:38

Hi Kris

Thank you for your response. I also notice very small changes. I too find that I frequently ask my optician to flick back to the previous lens before I make my decision whether the new one is better or worse, when we get toward the end of the eye exam. I think that when you are comparing two very similar lenses, and you are a person who wants to ensure that you have given a correct response, that it is natural to want to double check whether the new lens is definitely better than the previous one.

I find that my left eye never seems to correct quite as well as my right, which is the eye in which I have the stronger (although still small) prescription. My optician says that my visual acuity is the same in each, but I know that my right eye looks clearer. I wonder whether this is just the limitation of cylinder values going up in 0.25 steps, with my left falling between two values, or whether the axis could be fine tuned a little better.

I think it may be the 0.25 cylinder increments, as previous opticians have prescribed 0.50 cylinder for my left eye, and it wasn't until I started seeing my current optician, that my left eye cylinder returned to the 0.25 at which I have always been more comfortable.

Obviously I can't do anything about sphere values being determined in 0.25 steps, even if I can determine 0.125 difference in cylinder, but I am going to ask about my left eye axis values next time and see if I can fine tune them like Cactus Jack suggests.

It is however difficult with me now only having a 0.25 cylinder in my left eye. When I previously had a cylinder of 0.50, a previous optician amended my axis to 88 from 83 when I asked about it previously. He however said that as visually sensitive as I am, I fluctuated during the eye exam from always preferring the 88 to suddenly preferring the 83, and back again. I have no idea why this is the case. In my first eye exam with my current optician, who is very good, the very last thing she did, was ask me to choose between two lenses, and I said that I could see no difference. She laughed, said that she was not surprised, and I was comparing my now 0.25 cylinder at 83 and 88 degrees, and a 5 degree difference is tiny with a 0.25 cylinder. She split the difference and prescribed an axis of 85. Also having an old pair of glasses with a left eye axis of 80 with a 0.25 cylinder, and finding these fine, I'm wondering whether an axis of say 70 could be more accurate. I think I'll ask if I can fine tune next time and try moving the axis either way.

I feel that the best way to proceed for yourself, is to mention the previous refraction by a student, who found more cylinder, and your home astigmatism test, and ask your ECP whether he feels that you need and would accept a higher cylinder value in your prescription.

Best wishes


Cactus Jack 16 Apr 2018, 01:20


You might find this useful for your next eye exam.


An eye exam is not like an exam that you might take in school and there is really no way to study for it. However, you can prepare for it and learn about your role in the exam. The best eye exams are a team effort between you and the Examiner (hereafter referred to as the Eye Care Professional or the ECP). Part of the preparation is to learn what to expect, particularly if this is your first eye exam.

One important thing you need to keep in mind is that the ECP, has no way to experience what you are seeing. The ECP has to depend on your answers to important questions.

There are two parts to an eye exam.

The first part is the Objective part. This part consists of:

1. Taking a Visual History where you describe your vision and the kinds of problems you are having. Please tell the ECP everything. In some ways the ECP must be a detective and every clue is important.

2. Checking the internal pressure in your eyes for symptoms of Glaucoma. This is one of the very few parts of an eye exam that is even mildly uncomfortable and the discomfort only lasts for a few seconds. There are two basic ways to do the pressure test.

A. Using a special instrument to lightly touch your Cornea. No real worry there. Before doing this type of test a drop of mild anesthetic will make sure you donít even feel it.

B. There is a new type instrument that uses a puff of air directed against your cornea. No anesthetic is required, but the puff will startle you. The puff of air is harmless.

There are huge benefits to these simple tests to detect Glaucoma early, before it can do damage. Early discovery can save your eyesight.

3. The ECP will also get a preliminary estimate of your refractive error by using an Auto-Refractor or manually by using a small hand held instrument called an Ophthalmoscope or Retinoscope.

The Auto-Refractor is a relatively new instrument that was developed in conjunction with NASA to check Astronauts vision in space. You just look into the machine with each eye individually or in some machines both eyes are checked at the same time. When you look into the machine, you will see a scene or a pattern. The machine will adjust its internal lenses to focus the image you see, on your Retina. The Auto-Refractor only takes a few seconds for each eye and it then prints out your estimated prescription.

Some ECPs prefer to use manual methods that have been used for many years. Using an Ophthalmoscope or Retinoscope and a Trial Lens set or a Phoropter (a fancy machine with a built in lens set), the ECP will look into your eyes and select the lenses that allow him/her to see your Retina, most clearly.

This first part of the exam was to get to a starting place for the Subjective part of the exam where you have to describe what you see.

The second part of the exam is the Subjective part:

Typically the Subjective part of the exam starts with the Right Eye shutter open and the Left Eye shutter closed.

Step 1 is typically determining the Cylinder and Axis of any Astigmatism correction you need.

This is actually the hardest part of the exam because you will be asked to judge relative blurriness of two images rather than the relative sharpness of two images, which follows.

You will be shown a line of text and a supplemental lens will be rotated into place. This lens is a cylinder lens that is mounted on a 45 degree pivot. It can be flipped back an forth to bracket a ďtrial axisĒ or orientation of the long Axis of the Cylinder lens.

The thing that is confusing about this test is that the straight lines (strokes) of the letters will alternate in clarity as the lens is flipped back and forth depending on the direction of the stroke.

I suggest concentrating on an ďOĒ if possible. Depending on your answers, the ECP will adjust the axis knob unit the image you see is equally blurry with the supplemental lens 45 degrees each side of the selected axis.

At this point the ECP will probably swing the supplemental lens out of the way and may change the Cylinder power, while asking you which lens is shaper and clearer.

ďFine TuningĒ the Axis

If you have not had many eye exams, you may be uncomfortable asking the ECP to let you fine tune the Cylinder Axis. It is often beneficial to mention that you would like to Fine Tune the Axis at the appropriate point in the exam, before the exam starts. I have found that most ECPs will appreciate your wanting to actively participate in the exam.

The way this works is that the ECP will place your hand on the Axis control knob. This time, you move it back and forth a few degrees looking for the sharpest image. It is a bit like ďFine TuningĒ an old Analog TV set or moving the tuning knob on an analog AM radio for the best signal. As you move the knob, you may notice that the letters appear distorted (an uncorrected Astigmatism effect), all you have to do is stop moving the knob when the image looks the sharpest and has the proper shape. It is that simple.

The next step is determining the Sphere correction.

This is an easy part of the exam because all you have to do is pick the sharpest image, but there is a tricky part. Your auto-focus mechanism will try to help, if it gets a chance. The ECP has a couple of ways to minimize the action of your Ciliary Muscles and Crystalline Lenses.

The ECP can ďsneak upĒ on your Sphere prescription or the ECP can use drops to Dilate your eyes. Lets talk about sneaking up on your prescription first.

There are actually FOUR lenses* in your eyeís lens system, but for our purposes we will only consider two of them, the Cornea and the Crystalline Lens. All of the lenses are PLUS lenses. The total relaxed power of all the lenses added together is typically about +56 to +60 diopters. The only VARIABLE focus lens is the Crystalline Lens. The rest of the lenses are FIXED or SEMI-FiXED power. The PLUS power of your Crystalline Lens is controlled by your Ciliary Muscles. For distance, your Crystalline Lenses should be fully relaxed with a power of somewhere around +15 diopters. When you focus to read, your Ciliary Muscles squeeze the Crystalline Lenses to increase their PLUS power by the amount necessary to sharply focus the image on your Retina. The amount of additional PLUS needed, depends on the distance to the object. Typically around +2.50, but it can be a bit more, depending on how close you like to read. (See Presbyopia, below)

This will take a little thought to get your mind around, but if you are nearsighted (Myopic), your lens system has too much PLUS for the distance from the lens system to your Retina and you need MINUS lenses to neutralize some of that excess PLUS power. You ONLY have the ability to increase the PLUS power of your lens system. You have NO ability to reduce the PLUS power of your Crystalline lenses to LESS than that in the fully relaxed condition. (That is why people who are Myopic need external correction).

If you are farsighted (fHyperopic), your lens system does not have enough PLUS for the distance from the lens system to your Retina and you need PLUS lenses to focus images on your Retina. If Presbyopia does not prevent it, you have some ability to correct Hyperopia, internally.

To try to keep your Ciliary Muscles and Crystalline lenses from getting in the act, the ECP will start with NOT ENOUGH MINUS or TOO MUCH PLUS (optically. the same thing) and gradually increase the MINUS or decrease the PLUS, one or two steps at a time, while reducing the size of the line you are asked to read. ECP will not tell you what power lens or what line you are looking at. Eventually, ECP will reach the 20/20 line and a lens power that lets you read it with no mistakes.

The ECP will then follow the same procedure with your Left Eye.

When examiner has completed checking both eyes, he/she will open the shutters and you will likely see two separate images. This is intentional. This part of the exam is to check your muscle balance using some prisms that can separate the images both Horizontally and Vertically. ECP will probably ask you to tell him when the two images are aligned Horizontally and then Vertically.

While the images are separated, YOU have a very important check to make. Compare the sharpness of the two images. If they are not equally sharp, be sure and tell the ECP which image is clearer. If there is a difference, the examiner will likely reduce the sharpness of the clearest image until they match. The important thing at this point is that they match. That lack of sharpness will be corrected in the next phase with both eyes working together.

Next the ECP will fuse the two images so both eyes are working together and repeat the Sphere procedure by gradually increasing the MINUS or decreasing the PLUS simultaneously on both eyes until you see the 20/20 or sometimes the 20/15 line of letters, very clearly.

The final part of the exam is checking your near vision. This is done using a small chart about 14 to 16 inches or 35 to 40 cm from your eyes. The examiner will ask you to read the smallest (lowest) line you can without straining. If you need some near focusing help, the Sphere PLUS will be increased until you can read the very small text easily.

That pretty much completes the exam.

Many people, who wear glasses, actually look forward to eye exams. Once you have become accustomed to having very good vision, you will probably find anything less, unacceptable.

Many times, after the exam, it will be suggested that you com back for another exam, some time in the future. Note that I used the word ďsuggestedĒ. It is NOT a Command. If your detect a problem or if your vision seems uncomfortable, please DO NOT wait until the ďsuggestedĒ date to seek an appointment to get your vision checked.

If the exam is for a child, and it is their first exam, you can help relieve the natural anxiety by fully explaining what is going to happen and most importantly assure them that it does not hurt. You might even consider getting an exam yourself, first, while the child observes. Many ECPs are excellent with children, understand their apprehension, and will go to great lengths to make them comfortable. This is very important, The best exams occur when the patient is relaxed.

I hope this helps. If you have any questions, please donít hesitate to ask.

The FOUR lenses in your eyes are: (from front to back)

1. The Cornea, a very strong fixed focus PLUS lens. The usual source of Astigmatism if the front surface is not a evenly curved. Note that the Cornea is living tissue that DOES NOT have a blood supply. It must get is Oxygen and Nutrients from tears and the air.

2. The Aqueous Humor, a watery fluid between the Cornea and the Iris. It has very little PLUS, but its power can be affected by blood chemistry, particularly abnormal Blood Glucose (diabetes)

3. The Crystalline Lens, a very strong variable focus lens whose power is Increased (only) by the action of the Ciliary Muscles. The Crystalline Lens is affected by Presbyopia and also the lens that can cloud up and become opaque. A condition called Cataract which requires surgery to correct. Most Cataract surgery today requires about 15 minutes per eye. The clouded Crystalline Lens is emulsified and removed thru a tiny incision in the side of the Cornea and an Intra Ocular Lens (IOL) is put in its place. The power of the IOL can be selected to correct Myopia or Hyperopia if desired. Initial recovery is very fast (hours) and resumption of most normal activities (some minor limitations) the next day. It usually takes about 30 days for complete recovery and a final prescription.

4. The Vitreous Humor, a thick gel that fills the eyeball behind the Crystalline Lens and the Retina. It contributes some PLUS, but like the Aqueous Humor, its power can be affected by blood chemistry.

Note: For most vision correction purposes, we only consider the Cornea, the Crystalline Lens, and the Ciliary Muscles.

Kris 15 Apr 2018, 23:23

Lou and Cactus,

I found a couple of astigmatism screening tools online and my right eye screened for astigmatism each time (even with current correction). My left eye may have milder astigmatism, but not nearly as obvious as the right eye. I will definitely have to mention this to my ECP. Itís just a matter of figuring out how to accept the correction when heís dialing in the prescription.

Kris 15 Apr 2018, 19:04


I am wondering the same thing. I know that my vision improved in my right eye once I my ECP prescribed cyl. It has never been as clear as the left, but it is better. I find it takes some time to get used to the changes when my eye doc is testing my prescription and I have to make him go back because I feel like I would just be getting used to what he was trying and he would flip back to the other lens. I can tell something is different but it takes longer than they usually give to decide if it is better.

I feel like the way the doc tests my vision doesnít always work well for me. I am already perceived as someone who notices really small changes in my vision and telling him I need more time to decide what is working would add to my reputation. He has been very good with me and has changed my lenses twice at his expense when the prescription didnít end up working for me (When I first started wearing prism I adapted very quickly to the 2BO in each eye and went up to 4 BO within weeks of starting to wear prism).

Lou 15 Apr 2018, 15:23

Hi Kris

I'm no expert, just a reader, so please take my post in this context, but when I read about your monocular ghosting issues, my first thought was insufficiently/inaccurately corrected astigmatism. Since you are now saying that you could have more astigmatism that you are currently being corrected for, I think that this is something to discuss with your ECP, in association with telling him/her about the ghosting issues.

All the best


Kris 15 Apr 2018, 13:28

Cactus My Current prescription is L +1.00, 5BO R +1.75 cal -0.5, 5BO, 2.5 Add. I think my right is 1.75 (I gave the wrong number in an earlier post). Add and prism have been the same for 2 years and distance vision is pretty stable. I do prefer to read with screens/books closer to my face than 30 cm and suspect this will likely translate to needing a slightly higher than normal add when all is said and done. My ECP tells me to hold things farther away, but so far I haven't listened (until it's necessary to be able to focus). The symptoms I'm having are similar to the eyestrain symptoms I had prior to needing previous prescription adjustments (other than the ghosting, although it is something I've noted for quite awhile and seems to be associated with when I have more eye strain).

I had a student who did a detailed refraction on me years ago and commented that she detected astigmatism in both eyes (around -1 in the left and I think 1.5 5in the right eye), but which I didn't seem to "accept correction for" (her words). I know the brain can adapt to small disparities in vision and I have wondered if I would ever need more astigmatism correction. vision in my left eye has always been better than my right, even with correction. When my ECP tests my vision with best correctionI can see crisply with the left eye, but while I can make out the letters with the right, they are never 100% clear. I don't think this has anything to do with my current issues, but just an observation.

Cactus Jack 15 Apr 2018, 09:07


It would be helpful if you would post your complete prescription. I suspect what is happening is that for some reason your Ciliary Muscles are squeezing your Crystalline Lenses to help you focus on your Computer Display. Even though your Crystalline Lenses have become stiff, extended effort by your Crystalline Lenses will cause an increase in their PLUS power. Once that has occurred, when you stop using the computer, your distance vision will be a little blurry. It will remain blurry until your Crystalline Lenses can relax back to minimum PLUS power. Because of the stiffness, that can take a while.

Insufficient tearing action can make the problem worse by altering the PLUS power of the Cornea slightly both in Sphere and Cylinder. Many times when you are reading or using the computer, you really don't blink enough. Blinking distributes tears which moisturizes, lubricates, and feeds the Cornea. Remember, the Cornea has NO blood supply. It gets most of its Oxygen from the air, but some oxygen and all the nutrients it needs comes from tears.

You might find that wearing OTC reading glasses or cli[ on magnifiers of the appropriate power useful in for helping focus on your computer display.

Another factor, that can affect Corneal moisture is very low humidity. Low humidity in the Cold Country can rapidly evaporate Corneal moisture, Try using artificial tears more frequently and see if it helps.

Also, check out the Artificial Tears that have a 1% Carboxymethlcellulose Sodium component in a gel. It is a little thicker than water and takes a little longer to spread evenly over the Cornea, but it lasts longer.


Kris 14 Apr 2018, 18:03


Iím 48 and live in Canada. Iíve been wearing prism for almost 3 years and been in progressives for 9 years. My ECP checks regularly for cataracts and so far so good. He thought he saw the start of something when I first saw him 10 years ago, but there has been no change on subsequent exams. Iíve had ghosting issues periodically before, but this seems more pronounced but so do my irritated, dry eyes. Iíve been using eye drops which alleviates the dry eye feeling, but not the feeling of eye strain that Iíve been experiencing.

I should note that before I started wearing progressives I had issues with what felt like dry eyes which resolved once I went fulltime with my glasses. As well, I would find my distant vision blurry if I had been reading or using a computer for extended periods of time. It would take a bit for my eyes to relax and for me to be able to see clearly at distance (like my eye muscles locked to focus close and then couldnít relax afterwards). Iíve been using a computer a lot in the past few days and today found my distance vision very blurry until my eyes relaxed a bit.

With my ECP suggesting I would soon need to increase my prism prescription and with my current symptoms, Iím sure I will need some adjustments to my prescription. I just need to wait until I can afford the lenses.

Cactus Jack 14 Apr 2018, 13:23


If it is dry eye problems, you should be a able to get some relatively inexpensive things to try.

Eye Washes such as:

Sterile Saline Solution

B&L Eye Wash (fundamentally purified water)

Artificial Tears such as:

Refresh Plus with Lubricant (0.5% Carboxymethlcellulose Sodium)

I don't know where you live, some of the "house band" copies work OK.

For the Eye Washes, you can use them pretty liberally to wash out contaminants.

For Artificial Tears just a drop or two in each eye, every few hours is probably enough to supplement the tears you are making to keep you Corneas moist and lubricated.

If that does not help, you might be developing Cataracts. There are several different types of Cataract that cause really strange and annoying vision problems, including seeing ghost images with each eye individually.

Because you need Prism, most ECPs automatically assume that you need a change in Prism. What you are experiencing is not affected by prism. You have to be sure that your ECP understands that you are seeing ghost images with each eye, individually.

May I ask your age and where you live?


Kris 13 Apr 2018, 19:48

Iíve posted before about needing prism. It took me a long time to accept the fact that the double vision I was experiencing needed to be treated. Iíd had conversations about prism with my ECP, but played down my symptoms although heíd indicated it was a matter of when I would need to use prism. I was initially prescribed 2BO each eye, but within a month or so I was back with eye issues and went up to 4BO. A year later I was increased to 5BO and Iíve stayed at this prescription for almost 2 years. I will admit that at my last eye exam in the fall my ECP thought I could go up to 6BO each eye, but since my symptoms werenít too bad (noticeable when I was tired, but otherwise not too bad) I decided to hold off on the increase for as long as possible, since my ECP keeps telling me that my eyes will continue to adapt to the prism and demand more. My current prescription is Left +1, 5BO and right 1.5 cyl -0.5, 5BO with an add of 2.5.

In the past month or so, Iíve noticed a lot of eye fatigue, dry eyes and some slight drifting of images but I can still fuse images. Iíve also noticed ghosting of text when watching TV. Itís both eyes (I still see it when I close one eye) and present with my glasses on and off. Iím not sure if itís just a result of dry eyes or something else.

I canít afford new lenses at the moment, but as soon as I can, I will be in to have an eye exam if these symptoms persist. I feel like my need to increase prism isnít as obvious as it was earlier on in the process, but that I will still need further prism increases.

Roy 13 Apr 2018, 11:15


I thought I would add my thoughts after many years of wearing base-out prisms. In my 20s I was myopic (about -3.0 right eye and -6.5 left eye). I did not like the difference in the lens thicknesses and tried adding a base-out prism to the right eye to equalise the thicknesses of the outer edges of the two lenses. I found 4 prism diopters to be the right amount and my eyes adapted to it instantly with no problems at all. I also over-corrected the myopia by about 2-3 diopters in each eye.

The myopia over-correction did not increase my myopia at all, and in fact it reduced steadily from around age 40 to about -1.5 right and -4.0 left now. Combining this with presbyopia meant that I had to take away the over-correction and reduce the myopia prescription.

The prism was a different matter. Within a year or so of adding the prism I experienced constant double-vision when taking the glasses off.

To maintain a decent edge thickness I increased the base-out prism in stages. When I reached 6 out left and 10 out right I was happy with the appearance, and outer edge thickness, of the lenses and I decided not to increase it further.

However I soon started to get double-vision even with my glasses on, and eye tests revealed that more prism was needed, and several more increases have been needed over the years. I now wear (and need) 10 out left and 14 out right and it does seem to have stabilised.

Clearly this is a warning that not only will eyes adapt to base-out prism but they may then want more. As far as I know the double-vision cannot be reduced or eliminated except possibly by surgery. My lenses are very expensive too, especially for progressives.

Double-vision, especially at these high levels, is quite disorienting and I need to wear glasses for everything (even in the shower like Caroline) so be warned.

Soundmanpt 12 Apr 2018, 03:55


What has happened to you seems to be pretty common when anyone starts needing prisms added to their glasses. I think the doctors aren't really sure just how much prism you need so they start out with a small amount and adjust from there. You really started out with a very weak prescription for reading which i'm sure you probably only wore as needed. But it seems like you really did need the addition of prisms added to your glasses when you were prescribed with needing it. You were now wearing glasses full time. At some point your eyes changed and you didn't just need your glasses for close up but also for distance which is when you got bifocals. All this an a very short period of time.

Not long ago there was a young woman in the "Inducing myopia" thread not only wanting to induce myopia but she also wanted to experiment with prisms in her glasses as well. Several of us tried to talk her out of it but she said that she did in fact order glasses from Zenni not only with over correction of SPH but 5 degrees of prisms as well. She didn't come back and report anything after that. I am willing to help someone wanting to induce a reasonable amount of myopia because that is correctable with glasses or contacts and even lasik. But NOT prisms.

Cactus Jack 12 Apr 2018, 00:25


I need a lot more information from Paul that he might not want to discuss publicly. That is why I suggested a more private conversation.

I try to not mislead anyone and make sure they understand the pros and cons of a proposed action. The Eye Position Control System (my name) seems to be highly programable. You may find that it is not too late for some therapy or exercises.

I think one the problems with Prism is very similar to an Add for Presbyopia. Prism or an Add takes over some of the work of the eye positioning muscles or the Ciliary Muscles, optically, which reduced the amount of exercise they get. Muscles that don't get enough exercise, get weak, which requires more external help, which makes them weaker. etc.

The important thing in any vision correction is to enable a person to function comfortably in their visual environment.


Weirdeyes 12 Apr 2018, 00:10


Iím getting evaluated for vision therapy next week. I do have 1 base in prism for each eye, but I can manage without. I remember when they tested my eyes once they said I needed 8 base in prism. Iím only 21 and use a weak add at home. I have really messed up eyes.

Caroline 11 Apr 2018, 23:00

Prisms, no going back, a cautionary tale.

Hello Paul,

I thought I might recount my prism experience here, as I got a lot of help from CJ some years ago.

I am a middle aged nurse, and was about +1.0 and coping Ok but, I was having occasionalvision split into two when tired, and was given prism +3 each side base in,with +1 in the frame and immediately my vision comfort was better, on returning about 3 months later, the eye woman suggested an add for close work, as i had taken to full time glases with relish as the prism was so good, it piut a zing into comfy relaxed vision, things just looked better!

. She incressed my prism to 5 a side ( 10)and add +2 for close. I a few days I had adjusted to the new prism, such that I had double vision with glasses off, a bit frightening, but the add was so helpful reading bottles, and upside down IV drip flasks, that I persisted.

So now I am trapped with a recent increase to 6 a side ( 12) and wondering where it will all end up, as my eyes still tend to drift apart, getting used to the prism and wanting more being naturally lazy, turning out.

I even wear my specs under the shower, which causes my teen daughter much mirth!

. I think I may have been better to do eye exercises, initially ( I see some optical websites recommned them)and keep away from prisms.

My suggestion is dont go into prisms unless really needed, as once in.. never out, beware.

Maybe CJ and S/man PT remember me, I dont post here, but lurk.

Cactus Jack 11 Apr 2018, 17:28



I suggest we talk about this privately.


Paul 11 Apr 2018, 16:21

Does anyone here have actual experience (themselves or someone they know personally) becoming dependent on base-out prism without having any symptoms/need for the prism before they started wearing it? Iím curious if this is actually likely to happen, and how long it would take to be difficult to reverse.

Soundmanpt 12 Dec 2016, 10:44


I have been following your comments with Cactus Jack about your dryness problems when wearing contacts. You do understand that one of the main reasons you need to get your eyes examined and fitted for contacts is of course to determine what prescription your eyes need and even more important to check your eyes to be sure that they are healthy enough to wear contacts. And for the doctor to fit your eyes with the right type of contacts that should work best for your eyes. But even a doctor isn't always sure which ones will work best and that is why they provide you with trial lenses to wear for a couple weeks to see how they work for you. Then in most cases you come back for recheck and if your happy and the doctor is happy after checking your eyes then you get your supply of lenses. But not everyone is a perfect candidate for wearing contacts. It's very possible that your eyes just aren't compatible for wearing contacts. It really seems that your eyes are too sensitive as well as too dry to wear contacts comfortability for more than a few hours. I'm sure you don't want to be trying to use drops every few hours in order to wear them. Even worse if your eyes are constantly getting dry that isn't healthy for your eyes either. Admittedly I am not a big fan of contacts, but even less of a fan when someone is forcing themself to wear them. I'm sue you must have your reasons for wanting to wear contacts instead of glasses. But by wearing your glasses they won't cause you any of these dry eye problems you are having with contacts. Your glasses are only -1.25 so they certainly aren't very strong, so your lenses are nice and thin and your eyes should look very natural through your lenses.

Cactus Jack 11 Dec 2016, 11:48


The flatter BC CLs may allow more tears under the lens, but they can't create tears that are not there. Typically, dry eyes are more of a problem in winter and in low humidity environments because the tears that are there evaporate more quickly.

I am not sure, but the ECP may have been trying to get an idea of your ability to accommodate for near and quickly relax to distance.

You did not mention your age, but one of the symptoms of Presbyopia is the speed with which your Ciliary Muscles and Crystalline Lenses can change focus. When you are very young, your Crystalline Lenses have the consistency of freshly made gelatin dessert. As you get older, the Crystalline Lenses gradually become stiffer and it become harder for your Ciliary Muscles to squeeze them and they also become slower to relax. This slowness can result in intermittent blurriness, until the correct focus is achieved. Ultimately, your Crystalline Lenses will get so stiff that your Ciliary Muscles are not strong enough to change their power and you will need some focusing help, in the form of bifocals or progressives.

The idea that Presbyopia does not happen until around 40 is a myth. It can happen at any age depending on your genetic makeup, your visual environment, and the strength of your Ciliary Muscles. For their size, the Ciliary Muscles are the strongest muscles in the body, but like all muscles, if you don't use them, they get weak. Sometimes is tempting for a person with moderate Myopia to take off their glasses to read or do other close work. That is convenient, because people with low to moderate Myopia effectively have built-in reading glasses, but it has a downside risk. It reduces the amount of exercise your Ciliary Muscles get and speeds their de-conditioning, which makes the progression of Presbyopia faster.


curious 11 Dec 2016, 11:00

thanks cactus jack for your comments, you confirmed my suspicions regarding my eyesight in contact lenses. I am new to wearing them and guess I am more sensitive to how they feel, but they certainly feel like they get tight and dry after a few hours of wear. I went back after doing some more research and found that a flatter base curve contact lens may offer more relief for dry eyes. It took some convincing to get the optician to order a flatter size in. I have been trialing acuvue trueye 8.5 bc and will now try the 9 bc. what are your thoughts on triaing the flatter base curve?

also do you have any idea what test the optician was trying to perform getting me to look up and down repeatedly, im not sure what he was trying to achieve when I told him my problem is lens blurriness as the day goes on (drying lens).

Cactus Jack 11 Dec 2016, 10:09


Tears are VERY important for the health of your Corneas and the functioning of Contact Lenses. Dry eye problems are a big reason for contact lens problems.

Most contact lenses have some water content and some have very high water content, which is considered to be very beneficial. Insufficient tears can affect both your cornea and the optical power and characteristics of your contact lenses.

When you take out your daily wear contact lenses, don't though them away, but leave them where you can see what happens when they dry out. Then put a few drops of lens solution or water on them and watch what happens. Same thing happens in your eyes, but to a lesser extent.

Insufficient tears can also cause the corneas to have problems. The corneas are living tissue, but have no blood supply. They must depend on exposure to air for Oxygen and tears for Oxygen, moisture, and nutrients. Ideally, Contact Lenses float on a film of tears. The CLs transmit Oxygen and some moisture to the cornea, but it is less than what they would get if you didn't have the CLs in.

At some point, you may have to give up on CLs. I did, because of dry eye problems. Some dry eye problems can be helped by medications such as Restasis, but it doesn't work for every dry eye problem. Your ECPs are the best source of advice for your particular situation.

Hope this helps some.


curious 11 Dec 2016, 06:18

Hello, I have recently started trialing daily contact lenses and went back to the optician to have a check up of the trial lenses. I am intrigued to understand what the optician was doing and why and also to seek your opinion on whether my vision complaint is related to my dry eyes. I have been told by a previous optometrist that I have dry eyes and dry patches on my cornea and advised to use sodium hyaluronate eye drops. My prescription is -1.25 both eyes.

I explained that on the whole my vision is good in the contacts but it can go a bit blurry during the day and then clear up, I forgot to mention to him that it clears up after i put drops in but the optician decided to check my vision in more detail after I made the comment about vision going blurry in the day as I wear them, I had already read out the letters on the chart earlier and he seemed happy with that. He put the large electronic device over my eyes that changes lenses, couldn't really tell much of a difference as he was changing the lenses so fast! Then he gave me a handheld chart with different size print on , then instructed me to look at that for a few seconds then look at the distance eye chart whilst he held a lens mounted on a stick to my right eye whilst looking at the screen and handheld chart, he kept asking me to look at the chart and then up at the distance screen over and over again, again I couldn't really tell a difference and said so, what was he trying to do as I've never had that done before in any test?

I tried to tell him that my vision is clear but can go a bit blurry as the day goes on but clears up and that this doesn't happen when I wear my glasses so I'm led to believe it's the contact lens causing interacting with my eye/drying out?

Imogene 04 Dec 2016, 14:03


Thanks again! I guess when I get my new glasses I should wear them a few days in a row to really get used to them (?). I've mostly only worn my glasses at home after removing my contacts at night, but I think it's time I became more used to wearing them out in the world, and more able to easily switch between contacts and glasses.

Soundmanpt 02 Dec 2016, 11:27


You're welcome. It would make sense that you probably do notice even a small change in your prescription more now especially for seeing close up. Most likely you have had very little little change in your eyes over the past 10 or 15 years and your eyes were able to adjust to those small changes without any problem. But you are approaching the age where even a small change might be more difficult for your eyes to accept so easily. It may not be long before you might be looking at needing your first bifocals. Because you're only 37 you would likely want progressives so your glasses would continue to look the same as your single vision glasses.

I think you're going to find that your glasses are going to be slightly better for seeing than your contacts with the addition of the astigmatism correction. But your contacts should still work okay but you will notice that they don't provide you with the same sharp vision as your glasses. Now when you first put on your glasses don't be surprised if they make the floor look slanted or you feel a bit dizzy at first. That feeling will rather quickly go away.

Imogene 02 Dec 2016, 08:23

Thanks very much for your input, Soundmanpt. Makes me feel better that it wasn't something really odd going on. It was just strange to me b/c I've never had any problem adjusting to a small change in my prescription before. But I also wonder if it's partly b/c I'm getting older -- I'm 37 -- and think my near vision/ability to accommodate is starting to change a little bit. The dr also had me try a contact for astigmatism in my left eye (-.75) but it was really uncomfortable and also seemed to make things close up a little blurry, but not give me a headache (not sure if the contact was slightly too strong or if the toric contact just wasn't working well for me). So he said it was fine to go w/out for now, but did include a small correction for astigmatism for each of my eyes (-.5 for both) in my glasses prescription, which I've never had before. So, I'm curious to find out if things will be a little clearer with my glasses compared to my contact, once I get them.

Soundmanpt 30 Nov 2016, 11:17


You're nearsighted so you really shouldn't need your glasses or in your case contacts so much for close work. This is the one big drawback with contacts. You put them on in the morning and they remain on until yu are close to getting ready for bed. Your eyes don't need so much correction for seeing close up as they do for seeing distances. So most likely in order for your eyes to be comfortable when doing close work your eyes are going to be slightly under corrected for distances. If you were a glasses wearer you would do well by wearing your -2.25 glasses for close work and your -2.50 glasses fro distance. You may recall that when you first started wearing glasses you were able to see things close up quite well without glasses, but once you started wearing glasses, or contacts full time your eyes adjusted to seeing close up with your glasses / contacts.

If you had continued wearing the stronger -2.50 lens after a while your eyes would have adjusted and you would be fine. But there is no harm in wearing the -2.25 lens as you can tell yourself.

Imogene 30 Nov 2016, 09:40

Hi...About a week ago, I had an eye exam, and my prescription for my right eye changed from -2.25 to -2.5. The left remained the same...just a small amount astigmatism (-.5). When I tried the new contact the dr gave me for the right, my distance vision was ok, but after reading/using the computer/staring at my phone screen awhile, I developed a huge headache. This happened several times, sometimes on the left and sometimes on the right, and with a little blurriness as I was reading. Tried my old contact in the right, and the headache slowly dissipated. Went back to the dr yesterday, and he changed the contact prescription back to -2.25, but didn't have much explanation for the headaches/blurriness with the new one; he seemed to think it was strange b/c I consistently chose the -2.5 lens in the exam, and I, too, remember feeling like things were notably clearer during the exam w/ the stronger lens. Just wondering if anyone has an explanation. I also changed contact types/brands -- the new one is definitely more comfortable -- this couldn't be a factor, could it? (I'm using the -2.25 in the new brand now, but haven't done much near work w/ it in yet.)

Giovan 26 Aug 2016, 14:50


can you please provide a followup on your meeting with laurac from 2011?

it seems no one believed you and you told them to wait until you give her glasses.

i think you also said the name of the pub in italy. can you give it?

pelase. thank you.

Likelenses 25 Aug 2016, 22:06

Although this is a supposed eyesight improvement site the test seems accurate.

Astra 08 May 2016, 06:00


It is an unacceptable practice, for that doctor to discard your glasses. Even if the glasses is unnecessary or does not perform correctly, your glasses is your private property. she needs your consent before donating your glasses away without your consent.

That doctor is so bad , it looks like she thought oh -0.5 was not a high rx , but after she record so much data about acuity she did not seem to have a second thought on that

There are indication on that sheet. DVA stands for Distance visual acuity. your uncorrected acuity 20/25+3 which should be considered as 20/30 compared with corrected acuity (DVA) of 20/15. it is not only a slight difference on distance visual acuity . it is not uncorrected 20/15 with corrrected 20/15 .

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