What do you know about vision loss? It's not as simple as you might think! Read on so you can distinguish the facts from the assumptions and act now to prevent vision loss.

You don't see what you don't see

Sometimes vision loss due to glaucoma is depicted as "tunnel vision." Gradually, over time, the sides of the image go dark so that only the center is seen surrounded by a ring of blackness. But that's not truly what people with glaucoma experience.

Visual field loss does often start at the sides with the peripheral vision. However, many people with glaucoma don't realize there is a loss of vision because they don't actually "see" dark areas. There are no visible "walls" of the so-called "tunnel." People with peripheral vision loss just have a narrower visual field. People with normal vision see images of their surroundings and have a naturally limited range of vision. They do not "see" darkness all around them. People with glaucoma don't "see" darkness either they just see less of their surroundings.

Why is this important? Because glaucoma can steal your sight before you realize it's happening. Fortunately, you have started doing something about elevated intraocular pressure (IOP) and glaucoma. Stick with your treatment and see your eye doctor regularly to test your visual field and identify any damage to your optic nerve. With the tests available from your eye doctor, you should be able to understand and track any defects in your vision.

You "see" what you don't see

Glaucoma patients are often not aware of their loss of vision until the advanced stages of the condition. Researchers who study how the brain works have tried to explain this lack of awareness. One theory is that, when the retina or optic nerve is damaged, the area in the brain that processes visual input (the visual cortex) reorganizes the image it receives to mask the "defects" in the visual field. In other words, the brain fills in the broken image so that what you see appears to be whole.

You may be familiar with this ability of the brain from experience with a "blind spot" perhaps when driving. This "blind spot" is the area of the road behind and to the side of your car. Neither your sideview nor your rearview mirror reflects that portion of road, but your eyes and your mirrors may "fool" you into thinking you can see the whole road. Your brain makes assumptions in order to give you a more complete picture. It's a common phenomenon, but it also commonly leads to accidents on the road.

In the early stages of glaucoma, the brain may be able to form an image that seems complete. The brain may be able to "complete" the image by filling in the missing parts with the colors and patterns of the surrounding areas. However, there are many situations where this "filling in" can be hazardous to you and those around you. Let's continue with our car example. If a dog, cat, or even a person walks in front of your car, you may not see them. But not only that you may not know that you're actually not "seeing" that area of the road at all! If your brain fills in your blind area with surrounding input (color and texture of the road, curb, grass, etc.), how would you know that you're not getting the whole picture?

The impact of vision loss on your daily life

Several recent studies have tried to measure the effect of gradual vision loss over time. Just as people with glaucoma don't see "tunnel walls" or "blind spots," they may not understand the effects that vision loss may have on daily activities and the rest of their health picture.

Vision is more than just acuity (the ability to distinguish details). Many people with eye diseases such as glaucoma experience visual difficulties that affect their lives every day.

• Activities are limited
  Many people with glaucoma lose confidence in their ability to perform activities related to vision even before they report specific visual disabilities and long before they experience low vision or blindness. Of particular concern: glare, peripheral vision, and daily activities that involve adapting to light and darkness.
  
  
• Falls more likely
  People who have visual field defects that their doctors can measure (whether or not the acuity or sharpness of their vision is changed) are more likely to experience a fall.
  
  
• Traffic accidents more common
  Drivers diagnosed with glaucoma are more likely to be involved in a crash, compared with drivers of the same age without glaucoma.