LASIK for those with astigmatism: the toughest question

Having worked over the years with Noel Alpins, the Australian ophthalmologist who developed the Alpins Method of astigmatism analysis, the most common question I’ve heard from refractive surgeons—even well-known refractive surgeons—who are not actively employing the Alpins Method is: “Why not sculpt the refractive correction of astigmatism onto the cornea?”

Noel Alpins, developer of the Alpins Method of astigmatism analysis

Noel Alpins, developer of the Alpins Method of astigmatism analysis

Your refractive correction is the prescription that an eye care provider comes up with to maximize your vision through the use of lenses in front of your eye. If your natural human lens (crystalline lens) is cloudy, as happens with the development of a cataract, no kind of lens in front of your eye may help much. So then you may be a candidate for cataract surgery, which almost always is accompanied by the insertion of an intraocular lens (IOL). After cataract surgery, therefore, you may no longer need a lens in front of your eye, as the doctor has implanted a prosthetic lens inside of your eye.

Schematic of the vertebrate eye (photo be Rhcastilhos)

Schematic of the vertebrate eye (photo by Rhcastilhos)

But refractive surgical procedures such as LASIK and wavefront-guided LASIK work on your cornea, the clear dome of tissue at the front of your eye. So the cornea is not as far forward as the lens of your glasses, but is in front of an internal lens such as an IOL.

The doctor always figures out the optical difference between a lens in front of your eye (like glasses), a lens at the corneal level (like LASIK or contact lenses), and a lens inside the eye, like an IOL. This is simple optics, and not the subject of my current post.

Here’s the real controversy (or at least one of the primary controversies) regarding the use of LASIK to sculpt a refractive correction, in a patient with astigmatism, onto the cornea. Doing so may not be the optimal approach, and may not result in an optimal result. Yet thousands of refractive surgeons performing LASIK take that approach every day.

Dr. Alpins has shown that, by sculpting the refractive correction of astigmatism onto the cornea, you are attempting to neutralize all of the astigmatism that exists in the eye. And the overall astigmatism (which Alpins calls the ocular residual astigmatism, or ORA), is a function not only of the anterior surface of the cornea, where LASIK exerts its primary influence, but the posterior surface of the cornea, the fluids in the eye, the human lens of the eye, and the retinal eye-brain interface. Testing has shown that, in many patients, the astigmatism that can be measured on the anterior surface of the cornea does not match, by axis or magnitude, the overall astigmatism of the eye.

If you’re not a prospective or recent recipient of LASIK (or are close to someone who is), you’re probably not interested in the rest of this post. If you are, please try to hang in there for a few more minutes.

Sculpting the refractive correction onto the cornea may, in some cases, create a cornea with greater astigmatism than was measured preoperatively, and in other cases may leave astigmatism on the cornea in an undesirable orientation, or both. The Alpins Method allows the surgeon to examine, plan, and analyze the overall effects of LASIK and apportion the targeted correction between corneal and refractive astigmatism in a way that results in optimal vision.

Yet many, many refractive surgeons are not using the Alpins Method. Many are like orthopedic surgeons, who implant a Zimmer prosthetic hip, are taught the surgery by Zimmer representatives, and are thus compelled to use Zimmer tools. They may stick to that approach their whole career unless something comes along that makes their approach obsolete, and compels them in yet another direction.

As Dr. Alpins said in an article in Ocular Surgery News:

“…wavefront technology is providing us with some better numbers on the refraction because it has multiple values, but it’s still a refractive-based diagnostic number and not a solution for treatment.

“Those who promote wavefront refraction as the sole treatment mode to achieve what they call ‘super vision’ seem to miss the point that to improve the visual potential of an eye, one must reduce the amount of irregularity of the cornea by addressing the topographic disparity.

“Treating by refractive values alone, such as wavefront, can increase irregularity by attempting to correct the aberrations contained within the media of the eye on the surface of the cornea. This would produce less than optimal or even adverse visual outcomes in a significant proportion of patients.

“In the end, it has to be a marriage between [topography and wavefront], because you can’t just treat with one and disregard the other, which can give the patient an unpleasant refractive or topographic surprise.

“…[wavefront-guided LASIK is] useful in being able to model excimer surgery to better contour the cornea. However, if you attempt to neutralize all the internal aberrations on the corneal surface, you can create more of an irregularity, or a cobblestone cornea.”

The unpredictable process of corneal epithelial healing itself introduces the potential for an uneven cornea, he said. All these factors constitute a challenge for wavefront-guided LASIK.

He went on to note:

“It’s being suggested that topography is not as useful as we thought it was [with the advent of wavefront]. But I completely disagree with that. Wavefront analysis is fundamentally a refractive value. I believe topography is possibly even more useful because it’s the only way we can gauge how good or bad treatment employing wavefront analysis is doing.

“Those who promote wavefront refraction as the sole treatment mode to achieve what they call ‘super vision’ seem to miss the point that to improve the visual potential of an eye, one must reduce the amount of irregularity of the cornea by addressing the topographic disparity.”

I’m hoping to do a series of articles in ophthalmic and consumer medical publications on the management of astigmatism in refractive and cataract/IOL surgery. I’ll update you here on my progress.

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About Keith Croes

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Posted on August 18, 2013, in Medicine, Ophthalmology, Refractive surgery, Science, Technology and tagged , , , , , , , . Bookmark the permalink. 4 Comments.

  1. Been toying with the idea. Thanks for the great insight 🙂

    Like

  2. Great post! I’ve been doing a lot of research on this subject recently. Thanks for all the info!

    Like

  3. Thanks! Good stuff.

    Constructive criticism: Pet peeve of mine is reading the same quote twice, in whole or in part.

    Otherwise, I quite liked the article. With such a severe glasses Rx I’m interested in corrective surgery, but I’m waiting for my eyes to stabilize somewhat first, and the lack of clarity on eye surgery techniques is always somewhat opaque to me. Seems I’m not the only one 🙂

    -Nathan

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    • Some of the best refractive surgeons in the country can’t get by the central question of this article. I’m trying to persuade Alpins to come up with a 3-D animation that demonstrates the concepts involved. At your age, I’d imagine your vision is pretty stable. I mean, it’s never completely stable–wait till you’re my age, and then you have to deal with presbyopia. And soon thereafter, cataracts (if family history is any indicator–and it is). But a good refractive surgeon figures age and family history into the equation, and can at least set your expectations at the right level. Feel free to contact me offline if you want to discuss your particular situation. Fact is, refractive surgery can and has made a lot of people very happy.

      Like

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