We don’t think consciously about peripheral vision, but we use it all the time. That’s how drivers know a child has darted toward the street in pursuit of a ball. It’s also how pedestrians navigate through a crowd without constantly swiveling their heads from side to side. But peripheral vision can be the first thing glaucoma steals while we’re unaware that we have it. (You’ll find more about the disease at Horizon Eye Care’s Glaucoma page.)
Progression of Glaucoma
January is Glaucoma Awareness Month, a good time to think about a condition that’s usually far advanced before patients notice symptoms. Open-angle glaucoma affects about 95 percent of people with the disease. The more potentially dangerous closed-angle type occurs in the other cases. Open-angle glaucoma worsens slowly, and a doctor will detect it in an eye exam long before you realize you have it.
Healthy patients should be able to see approximately 110 degrees from the center temporally (towards the ear) and 60 degrees nasally (towards the nose). Glaucoma usually affects the nasal field first, then the temporal field, then central vision. If left untreated, it ends in blindness. (A note for drivers: The N.C. Department of Motor Vehicles requires at least one eye to have 30 degrees of peripheral vision off center in each direction – 60 degrees total – to meet requirements for a license.)
Though glaucoma affects both eyes, it can progress asymmetrically. Because your healthier eye compensates for the weaker one, it may rob 75 percent of your sight before you’re fully cognizant. Once both eyes are affected, you must turn your head to the side for your central vision to see what’s happening around you.
Causes of Glaucoma
Doctors have three theories about the causes of glaucoma. The first is mechanical. When the eye does not drain properly, fluid builds up and increases intraocular pressure (IOP). This compresses and damages fibers in your optic nerve, which sends light signals to your brain.
The second is vascular. Underlying problems such as hypertension, diabetes, smoking or cholesterol prevent blood from flowing adequately, starving those optic nerve fibers. The third is neurological. Some people produce more of certain types of neurotransmitters, which can be toxic to the nerve fibers.
Glaucoma more commonly occurs in older people and non-Caucasians. Patients whose family members have it are at higher risk themselves. A few activities are thought (though not proven) to worsen glaucoma. These include long-held yoga poses (when the head is inverted), scuba diving and wearing tight-fitting swim goggles.
Whatever the cause, doctors have only one weapon against it: Reducing IOP with drops or, in more severe cases, surgery. Doctors measure pressure with a device called a slit lamp. Normal pressure lies on a scale between 10 and 21, though you can have glaucoma with a reading as low as 12. Even if it’s not elevated at the start, doctors direct all their efforts toward lowering pressure in glaucoma. This is yet another reason why an annual exam remains essential.
Glaucoma Treatment at Horizon
To schedule an exam at Horizon Eye Care, use Horizon Eye Care’s Patient Portal or call 704-365-0555 Monday-Friday, 8 a.m. to 5 p.m.