Clearing the clouds: cataract surgery for astronomers: one amateur's journey through the medical maze of cataract surgery has lessons for any observer facing the same condition.
Coauthor Kathy's cataracts developed in her early 50s, just a few years after we became amateur astronomers. She started seeing multiple images of planets and fuzzy halos surrounding bright stars. The brighter the object, the worse it looked. Her eyeglass prescription began to change, skewing radically toward nearsightedness.
Fortunately, cataract surgery has become routine; a surgeon can simply remove the cloudy lens and implant a new one, and then you can go on as if nothing had ever happened, right?
Wrong. That myth applies only if you don't pay much attention to your vision. If patients don't know what a diffraction spike is, they might not notice the new ones in their field of view. But amateur astronomers pay close attention to what we see, and we most definitely notice the effects of cataract surgery. We even hear horror stories of people who have given up astronomy because of what the surgery did to their vision.
That's the bad news. The good news is that if you go into the procedure with both eyes open, so to speak, you stand a much better chance of coming out of it with vision that still works for astronomy.
We had heard other amateurs complain of diffraction effects from lens edges in the light path, so Kathy asked her surgeon for a large lens, one larger than her dilated pupil. But the largest replacement lens he would use was 6 mm, a dicey proposition for a relatively young person whose pupils might still open to 7 mm.
What's worse, the diameter of the replacement lens is only one consideration. When the surgeon removes the natural lens and implants the artificial one, the first step is to remove the front of the lens capsule, a clear, paper-thin sack of tissue that surrounds the lens, in a process called capsulorhexis. That opening typically has a smaller diameter than the lens, and for good reason: the lens capsule helps hold the lens in place, and a smaller opening helps prevent the migration of loose lens cells that might later cause cloudiness in the rear part of the lens capsule. But the smaller diameter of the capsulorhexis meant that Kathy didn't get a 6-mm clear aperture when she chose a 6-mm lens; the aperture was closer to 5 mm.
That was still better than having cataracts, so Kathy went ahead with the surgery. Cataract surgery is done one eye at a time. After the first operation, Kathy immediately noticed two improvements. Not only could she see clearly again in that eye, but because the cataract had been acting as a yellow filter, everything looked bluer, too. For the first few hours, she was very pleased with the outcome.
However, the moment she looked at a bright light that evening, she knew something was wrong. The eye with the new lens showed a huge diffraction spike around every streetlight and porch lamp. She saw more of the same when she looked through a telescope. Planets became bright bands stretching all the way across the field of view, as did any first- or second-magnitude star.
Ironing Out the Wrinkles
What had gone wrong? It turns out that the little wires called haptics that hold the lens in place were stretching the back of the lens capsule and, like cling wrap stretched unevenly over a bowl, the capsule had wrinkled. The wrinkle produced a diffraction spike far greater than the one caused by the spider in front of a telescope.
Kathy's surgeon wouldn't believe that the wrinkle was causing the diffraction spike. The wrinkle is so common that it's called the "in the bag sign," an indicator that the lens is resting properly within the lens capsule, yet few people complain about it. Many simply give up low-light activities. Incredibly, most people just don't seem to care.
But amateur astronomers care.
Kathy sought out another surgeon for the other eye, and he had good news. He would insert a ring to hold the lens capsule tight so the haptics wouldn't stretch it enough to wrinkle. It was a great idea, except for one problem: the ring didn't work. That's how common the wrinkle is: even efforts to prevent it aren't always effective. Now Kathy had two diffraction spikes coming off every bright light. Like the first one, the second spike was mostly horizontal, but cocked at a jaunty angle from the other, so she now had two wide bands coming off every bright light.
Sometimes the wrinkles go away with time as the capsules shrink around the replacement lenses, but Kathy's wrinkles stayed put. And to add insult to injury, she developed secondary cataracts, a common complication where leftover lens cells grow on the back of the lens capsule. Fortunately, the fix doesn't involve another invasive surgery. In a quick and painless procedure called a capsulotomy, the doctor uses a laser to remove the hazy section, essentially burning an opening in the back of the lens capsule.
But this procedure provides another opportunity for amateur astronomers to use expressive four-letter words. More diffraction! Surgeons don't like to cut big holes in people's eyes. That's generally a good thing, but with a capsulotomy, a small hole can mean a ragged edge in the light path. Even if the edge is relatively smooth, it's often polygonal, which can produce diffraction spikes going every which way.
Fortunately, our optometrist recommended a relatively new surgeon for the capsulotomies, one who was current on the latest technology and methods. During the pre-operative interview, we impressed upon him the severity of the problems Kathy was having with diffraction and her special concerns as an amateur astronomer. He understood her concerns and promised to make the biggest capsulotomy that he could make without endangering her eye or the artificial lens. And he promised to make the incision as round as he could.
He was good to his word, and after the procedure Kathy was pleased to see that the diffraction spike had disappeared in that eye. Even with her eye fully dilated at night, she could look at Saturn through a telescope without seeing diffraction.
She had the other eye lasered a month later with the same result: the diffraction spike disappeared. She didn't experience any problems from the edges of the capsulorhexes or the capsulotomies, probably because both openings are nice and round. Her eyes now perform as they did before the whole cataract ordeal began, and she looks forward to many more years of astronomy.
Though wrinkle-caused diffraction may be considered normal in cataract patients, we discovered you don't have to put up with it. Nor do you have to accept the optical defects that can accompany small capsulorhexes and capsulotomies. As with the rest of our optical train, amateur astronomers want the largest clear aperture we can get--with the emphasis on "clear."
As always when discussing medical concerns, your mileage may vary. Don't take this article as a prescription for what everyone with cataracts should do; rather use it as a guide for discussing your goals as an amateur astronomer with your surgeon. Medical constraints will guide what is possible and safe, but there are also optical constraints as to what's acceptable for amateur astronomy. Make sure both you and your surgeon understand what you want and how to achieve as much of it as medically possible. If you go into cataract surgery informed, you stand a much better chance of coming out happy.
What Is a Cataract?
The eye's natural lens consists mostly of long, thin, transparent cells called lens fibers. Over time, ultraviolet light from the Sun, and a host of other factors such as trauma or diabetes, can damage proteins in these cells, hardening and clouding the fibers. The cells change their index of refraction as a result, and they don't do so uniformly. Different parts of the lens harden faster than others, creating multiple focal zones. These changes muddy vision and may even create multiple images of the same object.
Kathy and Jerry Oltion have been amateur astronomers for about a decade. Jerry builds telescopes and many of his creations have been featured in Gary Seronik's Telescope Workshop column. View their website at www.sff.net/people/j.oltion. They thank Drs. Philip Stockstad, Steven Ofner, Mark Packer, and Matthew Neale for their assistance in restoring Kathy's vision and preparing this article.
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|Title Annotation:||Clear Eyes|
|Author:||Oltion, Kathy; Oltion, Jerry|
|Publication:||Sky & Telescope|
|Date:||Sep 1, 2014|
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