Explaining Astigmatism to Patients by a Visual Demonstration (unabridged version)

[Energy Conservation in Housing]

Explaining Astigmatism to Patients by a Visual Demonstration

By David L. Meinert, OD

At a lecture I attended on Astigmatic Contact Lenses, the lecturer (Dr. Wayne Cannon) asked, "How do you explain astigmatism to your patients?" I raised my hand, but was not called on. Dr. Cannon asked a couple of the doctors there, then continued on with his lecture.

I wanted to relate to the class how I "explain" astigmatism to patients. It invariably results in understanding, even getting amazement from some patients. The significant part of my "explanation" of astigmatism is a visual demonstration of astigmatism.

On later writing Dr. Cannon about my astigmatism explanation, he tried it on a number of his patients and found it very useful. He suggested that I try to have it published -- and referred me to the Optometric Economics magazine. (The article was published in 1995, though slightly abridged, compared to the below information.)

After I tell the patient they have astigmatism, and that it complicates things with contact lens fitting, most patients don't understand.

I then continue, "Astigmatism is not just a certain lens power, it is a certain power in a certain position." (Again, I usually get blank looks of non-understanding.)

I then take trial lenses (usually hand-held) of the full prescription and astigmatism power of one eye and occlude the patient's fellow eye. I then hold the lens power in place over the eye in the approximate axis position. I have the patient look at the chart, and ask, "So does that look pretty good?" Most patients then acknowledge that it looks OK, or fine.

Next I continue, "Now look what happens as I turn the lens." At this point, over about a three second period, I slowly rotate the lens axis 90°. I again ask, "How does it look now?" (Depending on the amount of the astigmatism, the patient may reply, "I can't see anything." or "It looks terrible.")

I then continue, "This is the exact same lens that gives you good vision." (as I now rotate the lens back to the proper axis). "However, if the lens gets out of position (rotating the lens again 90°), it doesn't work."

If the person already has a spectacle correction with about the same astigmatism, I explain, "You can do the same thing with your glasses, by (closing the temples and) turning the lens, the vision goes out of focus when the lens is out of position." (I usually show that to the patient also.)

I usually then continue, "Glasses are easy to make with astigmatism. Once the lens is made, the frame locks the lens in place and keeps it from turning. Contact lenses have no frame, and the lens is free to rotate out of position. For this reason contact lenses for astigmatism typically have to be "weighted" (made thicker on the bottom than on the top, and gravity helps it seek bottom* *) -- so that it always sits in a certain position on the eye. The lens power is then ground in the proper position. If the lens shifts while blinking, then the vision can still blur. The idea is to find a lens that stays on your eye in approximately the right position without turning much. That is A LOT more complicated than for other (spherical) patients that don't need a weighted lens. The astigmatic lens is more complicated and expensive for the manufacturer to make, and it is more time-consuming and expensive to fit. Which is why it costs you a lot more." (* * While giving this explanation, I typically use hand gestures to show the lens position . . . . That is to place my hands together, fingertips to fingertips upward, and heels of hands together at the bottom, to simulate "thicker on the bottom than on the top" and then show with hand gestures how the thicker part (heels of hand) would tend to stay near the bottom, even though I can show some rotation.)

If the person inquires how astigmatism got there, I will go into the corneal or lens causes of astigmatism, yet the vision result is very apparent to them. Some patients are so overwhelmed by the concept of an uneven power of prescription lens, that I have to repeat the trial lens demonstration a couple times. However, almost all the patients become keenly aware of the visual nature of astigmatism.

For incredulous parents, who want to know why it is so expensive for their child to have such a high-priced set of CLs, I simulate astigmatism on the parent. (This only works if the parent brought their glasses, or if the parent is emmetropic.) I then determine if the parent has reasonable acuity. I have the patient occlude one eye, and I place a plus cylinder trial lens, such as "pl +2.00 x 090" over the non-occluded eye, and ask, "So how are things now?" The parent typically acknowledges the blur. I explain, "This is what astigmatism is like." I then place a "pl -2.00 x 090" over the original plus cylinder lens, and ask, "Is that better now?" I explain, "This is astigmatism with the proper correcting lens in place." I again then rotate the minus cylinder lens slowly through 90° and ask the parent what happened to the vision. I explain, "This is astigmatism with the same exact lens out of position. This is why astigmatism is so much more difficult, since the lens has to stay in about the right position to make it work." This shows the parent the nature of astigmatism, and how important and critical the Rx lens orientation is.

When not dealing with contact lens patients, I also use trial lenses to simulate to (curious, disbelieving, or emmetropic) parents how blurry their child sees without correction. For example, for a child that has a final Rx of -1.50 sph, I simulate the blur, typically by holding a +1.75 sphere over the corrected or emmetropic parent's eyes. (I add 0.25 extra plus to the demonstration since I typically slightly underminus myopic children.) Such demonstrations often get better cooperation in getting the parents to purchase their children's glasses, and so that parents might insist the children wear their glasses.

I often use such visual demonstrations to reassure some overly anxious patients about their level of visual blur. I have some patients with a -.75 sph who feel their vision is so blurry. I then show them " . . . . How the rest of us live." I simulate for them 2D, 3D, and 4D of myopic blur by holding a +2.00 sph (saying "This is two units of nearsightedness") a +3.00 sph ("This is three units of nearsightedness"), and then a +4.00 sph ("This is four units of nearsightedness") over their correcting Rx while the patient views 20/200 to 20/400 charts. (This can be done also through the phoroptor, by adding equivalent plus, using phoroptor lenses, over their final Rx.) You can also reassure concerned 3 to 5D myopes that their eyes really aren't that terrible, by demonstrating 6 to 10 D of myopia with appropriate plus lenses.

On one occasion I was finishing the exam on a 6D myope who was recounting problems with her nearly emmetropic husband. "My husband keeps telling me I don't need those glasses, and to leave them at home. But he just doesn't understand how much I need my glasses." So I asked the patient if her husband was at the clinic waiting for her, and that I could show him an example of how blurry she sees. She said, "You could? That would improve our relationship 100%." So with the husband in the exam chair (and his wife watching), I found his unaided acuity was 20/25. I explained, "Your vision doesn't seem to be quite perfect, but it's really not that bad." I then showed him blur through +1.00, +2.00, +3.00 and +4.00 spheres. I explained that his wife's vision without correction is even worse than the lenses I showed him already. Presenting a 20/400 letter, I said, "Who could miss anything that big?" While placing +6.00 spheres over his eyes, he acknowledged how the letter was blurred beyond recognition. I explained "That's how your wife sees without correction. So you can't make light of her needing to wear glasses. She sees that blurry without them."

It typically takes less than 2 minutes to give a demonstration and explanation of astigmatism (or other refractive error), and it gives the patient a fairly complete understanding.

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About the Author: David L. Meinert is a 1977 graduate of the Illinois College of Optometry. He was a U.S. Army Optometrist from 1977 to 1987 and worked as a staff optometrist for Kaiser Permanente in Northern Virginia from 1988 to 2010.