Exploding Eyeballs (How Not to Have)

(Note:  You can search for medical accurate information on the Internet.  This isn’t it. My discussion below is a light treatment of a medical condition, written for people who don’t need to know details. Consult an ophthalmologist, visit your optometrist, and the sake of your vision, get your eyes checked every year or so, or more often if you have changing vision, a family history of glaucoma or any other eye disease, injury to your eye, dry eyes, and so on.)

Overview of your eyeball. Well, not YOUR eyeball, but an eyeball. (from eyecare-for-you.com)

Your eyes are really complex little devices. Under your sclera, at the outer edge of your iris and sort of under your cornea, you have this area called trabecular meshwork, which is where the fluid behind your cornea and in front of your iris drains out to maintain your intraocular pressure (IOP, inside your eyeball, that is). It’s sort of a filter whose function is to regulate that pressure by controlling the outflow of fluid.

In glaucoma, the IOP is too high, and compresses the networks of blood vessels, cutting off blood flow to the nerve mat and optic nerve. Over time, this high pressure and decreased blood flow damages the optic nerve, and the nerve and vessel mat in the eye, and leads, eventually, to blindness.

Comparison of optic nerves. Some of the instruments use also measure the density or thickness of the layers of nerves and vessels. Thinning layers is another sign of the disease.

It is an irreversible loss of vision. The ‘puff of air’ test that people hate is a quick test to determine pressure, but more accurate measurements are available and should be used if indicated. I’ve been having the tests done since I was in college. Why, when usually it doesn’t start showing up until around the age of 40? Glaucoma doesn’t hurt. You only know you have it through pressure tests, visual field tests, and pictures of the back of your eye. My great-grandfather died blind. My grandfather had some treatments to use, but had degraded vision. My mother has degraded vision (she only went to the doc when she needed a new prescription, and so wasn’t diagnosed until she was around 65). Who knows how many generations back it goes? I’ve already warned my sons to be tested regularly. I’ve had mine controlled with prescription drops. It’s serious business.

Comparison of visual field tests. When you don’t see one of the flashes of light, the computer maps the location. The dark area on the right shows the areas of the eye that don’t register due to glaucoma damage. The dark spot on the left is the optic nerve.

 

My vision loss in one eye means the best I can see, corrected,   20/100.  (For those playing along at home, my contact lens prescriptions are -9.0,  -7.5) The scans that a good eye doctor does for you will include a visual field test, where you start into  an apparatus and push a clicker when you see tiny flashing lights in your peripheral vision. The mapping of your results shows where areas of your retina you have lost vision.  An OCT scan will show the thickness of the layers in your retina. Together, they can help identify problem areas. I have the classic vision loss pattern. It’s been held steady for the past few years.

Back to the picture – by thinning out the trabecular meshwork, you can remove some of the resistance to outflow. It used to require surgery, but now can be done with lasers. That’s right, I have a laser pointed into my eye (don’t try this at home.)

The little device that aims the laser to your eyeball! No sharks were injured.

The procedure I had is called Selection Laser Trabeculoplasty (SLT). The doctor aims the laser into the little angle where the meshwork is (see the diagram) and burns out tiny bits of the meshwork, opening it up to allow the aqueous fluid to drain more easily. In the full circumference of the eye, there might be around 100 tiny bursts. They normally do one-half of one eye at a time. The discomfort is minimum, just some irritation that lasts maybe an hour or so. In my case, the pressure reduction after one-half of my eye treated in was four points.  (This is measured in mmHg, not psig which is the unit I use in my profession. I suspect 15 psig would cause my eye to go all esplody.)  Alas, no friggin’ sharks are involved in the deployment of said lasers.



Categories: health

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3 replies

  1. Very interesting (and timely too)! Matt and I have appointments with our ophthalmologist next Thursday.

      • More timely than I could have imagined. My pressure reading was a bit high. I’ve scheduled a followup visit for a recheck in January as pressure can fluctuate a bit and mine wasn’t significantly higher than it has been through the years – 21 rather than 19 or 20. It’s good to build a medical history by having regular exams particularly when a complete family medical history is unknown. I don’t know if there is a history of glaucoma in my family or not. My father’s family was extremely dysfunctional and I know little to nothing about them.

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