The Strabismus Institute
Part 2 – The Exam
“Please have a seat, Jack. This exam will take about an hour and a half, depending which movie you would like to watch.”
“Maybe one of the Star Treks, if you have them. I remember there was one where Kirk had to get reading glasses because he could not tolerate the 25th century drug that prevented presbyopia.”
With a chuckle, Jim said, “Yes, that was a good one, there are lots of people who wish we had that drug today, to avoid their bifocals and trifocals. I am pretty sure we have all of them in our library. Miss Jones, would you load that Star Trek, please?”
“Before we start the test and the movie, I would like to get a better idea of your eye motility. Here is a patch. Please cover one eye and follow my finger as I move it around. . . OK, that was good. Now, cover the other eye and follow my finger again. . . Now, take off the patch and follow my finger.”
“Your primary problem is that your eyes would like to turn inward or cross, but it looks like you have excellent range of eye motion. I think your problem is high esophoria rather than esotropia. We need to find out how much they would like to turn inward when both the muscles and you are fully relaxed.
As you watch the movie while looking through this machine, which is similar to a phropter, it will vary the amount of prism correction to find the prism values where you can fuse the images comfortably and the points where you break fusion. It will find both the minimum prism you need, the maximum you can tolerate, and the value where your eye muscles are most relaxed and comfortable.
You said on the questionnaire that you wake up with double vision. Also, that your glasses don’t always fuse the images for you and can’t keep them fused until some time after you wake up. Ideally, after this test, we will know how much prism you really need to fuse the images and keep them fused.
Use this button to tell the machine, when the image is fused and when the image breaks fusion. Press the button and hold it when you see two images and release it when you see only one image. The machine will either increase the amount of prism or decrease it to try to fuse the images for you.
The machine will cycle from too little prism to too much prism in a program that is designed to determine your fusion range. One of the reasons we like to use movies is that ideally, you will concentrate on the movie, rather than the test. Also, we like to use movies at least 1 ½ hours long to introduce an element of fatigue. Ideally, we will be able to plot the relaxation point where your eye positioning muscles and your eye muscle control system can be fully relaxed. From that, we can determine the amount of prism it takes for your eye muscles to be relaxed and the images fused.
Does any of that make sense, Jack?”
“I think it does, Jim. Can I stop the test if I want to?"
“Sure, but it is best if you can do it without interruption.”
“OK, Jack. Take off your glasses and look through the machine at the screen. I want you to be comfortable during the movie. This will be the initial calibration of the machine. We are going to start with a quick refraction to get your sphere and cylinder as close as we can.
This machine also has a built in auto-refractor. It will do both eyes individually and then both together. Look at the screen and stay relaxed.”
The machine started its cycle and I watched the patterns and letters on the screen get progressively clearer in each eye as the lenses changed. In a few moments, both shutters opened and I saw two clear images of a standard Snellen Chart. I was pretty confident that I was seeing at least 20/20, maybe better.
“We are going to start with you seeing two images. I will add Base Out prism until the images fuse. Try not to force fusion, let the lenses do the work.”
“I see two images now. Right now, I am seeing two separate images with no overlap. . . Now they are coming closer and beginning to overlap. . . They are overlapping more and more . . There! Now, they have fused into one image.”
“OK, Jack, close your eyes and let them relax for a minute or so.”
“Now open your eyes. Did you see any momentary double image or was the image fused when you first opened them?”
“I saw two overlapped images for just a second and now I see one image.”
“OK, Jack, that is common. I am going to increase the Base Out prism some and we will repeat the closed eyes routine again and see if you get the momentary double image. Close your eyes.
Try to keep your eyes relaxed . . Now open your eyes.”
“The overlap was much less, but it was still there.”
“OK, just a little more Base Out, and I think we will have a starting point. . . Same routine, Jack. . . Close your eyes. . . Open them.”
“No overlap that time. The images are fused”.
“Jack, that is 10 diopters more Base Out prism than you are wearing in your present glasses, no wonder you have been having some trouble with double vision. Now let’s see where the images break. I am going to reduce the Base Out prism slowly, try to keep your eyes closed a little longer than you usually do when you blink and tell me when you see two images again.”
“Right there, Jim, I see two slightly overlapped images.”
“OK, Jack. That broke a little sooner than I expected. We can now start the movie. I am pretty sure you need more prism in your glasses than you are wearing now.”
I sat there, enjoying one of my favorite movies, as the machine and I did our work. Occasionally, the images would break and the machine would back up until the images fused again, but I could tell that the total prism I was wearing was gradually increasing and I was beginning to get tired, but strangely, my eyes didn’t feel tired. Finally, the movie ended and Jim was waiting for it.
“Jack, right now, you have much more prism correction than you have been wearing. How does it feel, do your eye muscles seem to be pulling?”
“No, my eyes actually feel very relaxed and comfortable.”
“OK, Jack, I want you to continue to look through the machine for a few minutes with the prism in place, while I make up some trial frames with that prescription. Would you like to watch a cartoon? Personally, I think some of the Bugs Bunny cartoons are classics. I really like the one where Bugs sings Wagner.”
“No, that is OK, I think I will just sit here.”
A few minutes later Jim returned with the trial frames. “OK, Jack, I have your sphere, cylinder and prism in the trial frame. I would like you to close your eyes, sit back, and I will place the frame on your face. . . Now, open your eyes. What do you see?”
“Man, everything is sharp and clear and I only see one image.”
“Look around and see if there is any tendency to break fusion. Try different distances. We haven’t done anything yet to help with focusing close. I will be back in a few minutes.”
Jim returned when he said and asked, “What do you think now?”
“So far, everything is fused, but I can tell that I have to move my head more because my eye motion is somewhat limited. How much prism am I wearing?”
“Jack, you are wearing 32 diopters Base Out in each eye, for a total of 64 diopters of prism. When you came in this morning, you were wearing 20 Base Out in each eye. During the movie, there was one occasion where you got up to 43 Base Out in each eye, but you broke fusion and the machine had to back off for you to fuse the images. You actually were wearing 32 BO in each eye for the last 30 minutes of the movie.”
“Wow, I knew I needed more prism in my glasses, but almost double?”
“That is not uncommon. Many practitioners have been trained to significantly under correct prism in the belief that under correction will slow down esophoria. Our experience is that esophoria is a bit like myopia, we don’t know the actual cause, but under correction seems to make no difference in the final outcome and the only result of under correction, is reduced functionality and comfort for the patient.
Actually, 32 BO may not be exactly what you need. I will to get our specialty lab to make up a pair of glasses with this prescription so you can wear them more comfortably than wearing that trial frame. Our lab is used to making high prism glasses so they should be ready in a couple of hours. You really need to wear them for a couple of days and then we need to do the test again. While you are waiting why don’t you check out our library, there may be another movie you would like or you can pick out the one you want to watch when the do the test again after you have worn your glasses for a few days. Also, check out the break room, off the library.”
True to his word, about 2 ½ hours later, my 32/32 BO glasses were ready. I had worn the trial frames for most of that time. As Jim had suggested I visited the Institute’s break room. It was there that I noticed that I was not the only “guest” wearing a trial frame with significant prism. Hmm, maybe other people have similar problems.
When my glasses were ready, Miss Jones adjusted the fit for me. I was really surprised at how sharp my vision was with the high prism lenses and how comfortable they were. As an experiment, I put on my 20/20 BO glasses back on and discovered that they were no longer very comfortable and while I could still fuse the images with much effort, I had already grown to like wearing more prism.
Jim came in and asked. “What do you think?”
“I am amazed at the optical quality and the comfort of these new glasses. I tried going back to my 20/20 BO glasses and I don’t like them much now that I have had a taste of what I really need.”
“Yes, our lab really knows how to make high prism glasses.”
“Jack, I assume you drove yourself, here. Is that correct?” I nodded. “I need you to go back to wearing your 20/20 BO glasses for at least a half-hour before you leave here and wear them while you drive home. When you get home, switch to your new glasses and wear them as much as possible, but I would prefer that you not try to drive with them for a few days until you get used to wearing them and we do some checks. I think you are pretty close to the legal limit for peripheral vision for driving, but we are not ready to check that yet.
Today is Tuesday, could you come back on Friday morning wearing these glasses and ask someone to drive you? You need to plan for it to take most of the morning. Your driver can explore our movie library while they are waiting. We have over 1000 titles on DVD and Blu-Ray. Some are in 3D.”
“I’m pretty sure I can get someone. And, I will try to wear them from the time I wake up until I go to bed.”
“We haven’t done anything yet, about your reading add. Here is a pair of clip on +2.50 readers that you can use for close work and a pair of +1.25s that might be helpful if you want to use the computer. Just in case you need them.”
“I’ll see you next Friday. Miss Jones, would you set up Jack’s appointment please?”
“Thanks, Jim. I can’t believe I am wearing 64 diopter glasses that are this comfortable and have this quality of vision and no double vision.”
“I know it is tempting, but please go back to your 20/20 glasses for a half-hour before you drive home.”
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