Imagine waking up one morning to discover that your vision is suddenly blurred. Over the next few days it becomes progressively worse until you can no longer make out the numbers on the alarm clock, and the picture on the wall is a jumble of fuzzy, colored patches. After a visit to the ophthalmologist, you learn that you have optic neuritis, an inflammation of the optic nerve. The inflammation gradually subsides over the next several weeks. Your vision improves, but you are left with a partially blind region in the center of your visual field reducing your acuity to 20/80. You would probably be able to read the newspaper with a magnifying glass, to navigate without the aid of a cane, and to recognize familiar faces that are nearby.