SKY_September2014.pdf

36 September 2014 sky & telescope

Clear Eyes

the new lens showed a huge diff raction 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

fi eld of view, as did any fi rst- 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 diff raction 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 diff raction 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

eff orts to prevent it aren’t always eff ective. Now Kathy had

two diff raction spikes coming off every bright light. Like

the fi rst 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 complica-

tion where leftover lens cells grow on the back of the

lens capsule. Fortunately, the fi x 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 diff raction! 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 diff raction spikes going

every which way.

Fortunately, our optometrist recommended a rela-

tively 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 diff rac-

tion and her special concerns as an amateur astronomer.

He understood her concerns and promised to make the

A healthy eye’s view of Saturn through a telescope.

Kathy’s cataracts blurred and broke up the image.

After her fi rst procedure, Kathy’s daytime vision cleared signifi cantly,

but a large diff raction spike destroyed her nighttime vision. After

both eyes had been operated on, a second diff raction spike (not

shown), cocked at a jaunty angle, joined the fi rst.

WRINKLE The

haptics that hold

the replacement

lens in place stretch

the lens capsule and

can create a wrinkle.

This common eff ect

can create diff rac-

tion spikes in the

line of sight.

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Capsulorhexis

Wrinkle

Haptic

Lens edge

Cataract layout.indd 36 6/23/14 12:17 PM