Section 1-C: Understanding Vision Loss from Glaucoma

Central vision is the fine vision people use to read and recognize faces, while peripheral vision is the side vision that is used for navigating obstacles in the environment (like doorways and coffee tables) and for detecting oncoming vehicles from a side street. The diagnosis of glaucoma is often made late in the disease course, because early stages of glaucoma are usually characterized by loss of peripheral vision and sparing of central vision. Patients often fail to notice peripheral vision loss until it has progressed towards the center of vision. Unless the patient happens to be examined by an eye doctor, they could be unaware that they have glaucoma. The only way to be diagnosed with glaucoma in early stages is to be examined by an eye doctor and undergo an eye exam and visual field testing, which measures the amount of vision loss from optic nerve damage (Figures 1-10 to 1-14).

	Figure 1-10. Normal Humphrey visual field test. This is a side vision test which is performed to diagnosis glaucoma. There are no dense black spots indicating vision loss.
	Figure 1-11. Superior arcuate visual field loss from glaucoma – as tested by Humphrey visual field device. The black areas represent abnormal blind spots corresponding to areas of vision loss.
	Figure 1-12. Superior and inferior visual field loss from glaucoma causing tunnel vision. Despite the peripheral vision loss, central vision is still intact and the vision may be 20/20.
	Figure 1-13. End stage glaucoma with dense superior and inferior visual field defects – as tested by Humphrey visual field device. Central vision is now gone and there is severe visual impairment.

Figure 1-14. Visual field testing with a Humphrey Field Analyzer device shown here is a standard method for monitoring glaucoma.

The nerve fibers of the optic nerve spread from the nerve head and arch superiorly and inferiorly, meeting at an anatomic line called the horizontal raphe. Glaucoma tends to affect the superior and inferior parts of the optic nerve first, thereby producing arching or arcuate visual field defects. This explains the characteristic pattern of visual field loss in glaucoma. Because of the anatomy of the eye, when the superior part of the nerve is damaged, patients will develop inferior visual field loss. Conversely, when the inferior nerve is damaged, patients will develop superior visual field loss. Since the center vision is usually spared, visual acuity may be 20/20 at least until the center vision is finally affected late in the disease course. In certain forms of glaucoma the central vision can be affected early in the disease process. When the central vision is affected, patients will often notice the vision loss and seek medical help. In this case, patients may notice a black (blind) spot in their vision.

Figure 1-15

If optic nerve damage occurs both superiorly and inferiorly, the two arcuate visual deficits can meet, resulting in tunnel vision. Even at this advanced stage of glaucoma, the vision may be 20/20. However, if the center or fovea is affected (which typically occurs in endstage glaucoma), the vision will get worse. At this point, most of the vision is gone and patients may have difficulty functioning independently.

The visual field test determines the extent of peripheral vision loss. This, in turn, corresponds to the cupping of the optic nerve with glaucoma. Visual field defects from other types of eye diseases may also be detected during visual field testing. Glaucoma has characteristic visual field defects, which correspond to the anatomic distribution of the nerve fibers. Particular patterns of visual field loss can be used to diagnose glaucoma and distinguish it from other eye disorders.

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