By Dr. Charles J. Bock

Prism Convergence Exercises

By the time you have been given this handout, you have probably been told about convergence insufficiency and some basic exercises (jump convergence, pencil-to-pencil) to treat it. Below, you will learn about prism convergence exercises, which are a very effective treatment for convergence insufficiency.

About your prisms

The box of prisms you have purchased contains one red glass (with no prism power), and pairs of prisms in strengths of 5, 10, 15, and 20 prism diopters (a prism diopter is a unit of measurement). Keep your prisms in the padded case when not in use, and clean only with mild soap and warm water. Dry with a soft cloth. Do not ever use alcohol to clean your prisms.

When performing the exercises below, always hold the prism with the numbered edge pointing away from your nose, regardless of whether you are using the prism over your right or left eye. Do not tilt the prism in any direction.

About the exercises

The first exercise you will perform will be to help increase your convergence for distance and near. You will need: a light source, a 20 foot hallway, and a pencil. The light source may be a candle or a single small light (such as those found on a strand of Christmas lights). If using a light, it will help to poke a single bulb out through an opaque box, such as a half gallon milk carton.

Place the light source above waist level at the end of a 20 foot long space (for most people a hallway works best). Stand 20 feet from the light. Hold the pencil by its eraser one foot in front of your nose, with the tip of the pencil pointing straight up, and centered in front of your eyes. Before using any prism, look at the light source. Close one eye and then the other. Notice that the pencil appears to jump from one side to the other. With both eyes open, you will notice that there are two pencils but one light. This is very important. If you are using both eyes to look at the target, you should see two pencils and one light. If you see only one pencil, you are not using both of your eyes together.

Next, hold a 5 unit prism in your right hand with the number pointing out (the narrowest side of the prism will be next to your nose). Looking at the light, with the pencil in front of your eyes, be sure that you see one light and two pencils. Walk slowly toward the light, one step at a time, pausing after each step. If you can get to within a foot or two of the light, stop, then walk slowly backward to the starting line. If you see two lights or are unable to see two pencils and one light before you get near the box, stop at that point and back up to the starting line. With time, you will get closer and closer to the light. Do this for 10 to 15 minutes. You may need to take brief rests or split your time into a couple of sessions.

Once you can comfortably do this with a #5, try it with a #10. You may find your progress very slow, and it may take a week or more to move from one prism to the next. Even if one level is easy for you, do not advance from one prism to the next for at least 3 days.

You will continue this, advancing up by 5 units at a time, as you tolerate it. Some people find the exercises very easy at first, but have difficulty once they reach 15 or 20 units. Do not despair. This is hard work, and it takes time. Please call our office at any time if you get frustrated or need to discuss your progress.

Once you reach 20 units, your next jump will require that you hold a prism in each hand (see the chart below). Some patients try to dangle the pencil from the brim of a visor or baseball cap, while others ask someone to hold the pencil for them.

Advance as follows:

If you can get to 40 total units, you are doing great! This takes time. Do not expect to be much beyond 15 units after 4 weeks.

Reading with prism

Once you can comfortably do the basic exercise with 15 units of prism, you should begin reading with prism. Begin with a 5 unit prism. Place a book or magazine on a flat surface, 18-24 inches from your eyes. Hold a pencil (as above) in your left hand and the prism in your right. You should see two pencils, one on either side of the word you are reading. Try reading this way for 15 to 20 minutes per day. Most patients find this to be an extremely effective exercise. Advance in 5 unit increments until you can read with 20 units of prism.

Watching television with prism

Once you can comfortably do the basic exercise with 15 units of prism, try watching television with the prisms. Using a pencil and a 5 unit prism, watch television for 15 to 20 minutes a day. Advance in 5 unit increments up to 20 units of prism. Holding a pencil this long can become tiring. If you are sure you are keeping your eyes focussed together, you may put the pencil down, and pick it up every few minutes to check yourself.

How much longer do I have to do this, doctor?

Many patients have a significant improvement in their symptoms after just a few weeks. You will have the greatest benefit and the lowest chance of relapse if you stick with the exercises until the end.

If you have questions

Please call our office 503-656-4221 at any time with your questions. This program is very effective, but requires a lot of effort on your part. We want you to feel comfortable doing the exercises and we want to hear from you if you are having any problems or questions. Many patients need to call us after trying the exercises at home to be sure they are doing the exercises correctly. That is why we are here. Do not hesitate to call.