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The images above the photographs of the couple represent formal visual field testing performed at the doctors office. The 2 left figures represent left eyes with inferior defects and the two figures on the right represent right eyes with superior defects. Put into real life situation the photograph of the couple above schematizes what can happen when glaucoma damage becomes advanced. The picture on the left is normal, but notice that the picture on the right has a "tunnel vision” appearance. This occurs when the defects detailed in the upper figures are present in together in one eye.
In advanced cases of glaucoma vision loss can extend into the central area and people become functionally, and legally blind. People often note other impacts to their vision as glaucoma progresses. Contrast sensitivity, or the ability to discriminate similar shades of colors is hampered. This can manifest in difficulty identifying each step on a stairwell. In addition, light/dark adaptation is slowed. This results in an abnormally prolonged time to adjust to new lighting conditions, like walking into a dimly lighted house from a sunny day.
The single greatest risk factor for, and often the direct cause of glaucoma is abnormally high eye pressure (normal eye pressure is below 21mmHg). In order for vision to be normal the eye must pressurize itself. There is a very elegant mechanism responsible for this pressurization and can be abnormal in multiple ways resulting in obstruction of the fluid from leaving the eye. This has resulted in glaucoma being classified into 2 categories:
Not all cases of glaucoma have high eye pressure. Some patients develop progressive glaucomatous optic nerve damage despite maintaining statistically normal eye pressure (22 mmHg or lower). The results of the Normal Tension Glaucoma Study (NTGS) demonstrated that lowering eye pressure by 30% was effective in slowing vision loss in a large percentage of participants in this study.