This study will examine whether direct current (DC) polarization (electrical stimulation) of the visual cortex can cause a temporary improvement of vision in an amblyopic eye of an adult. Amblyopia (also called lazy eye) is reduced vision in an eye, caused by abnormal brain processing of visual information. In amblyopia, the visual cortex (the part of the brain that processes visual information) favors the other eye and suppresses the image from the amblyopic eye.

Amblyopia in children is treated by patching or blurring the good eye, which forces the child to use the amblyopic eye and overcome suppression by the brain. This treatment only works in children 8 years old and younger, however. Electrical stimulation of the brain can temporarily change the function of the visual cortex in adults with good vision, but its influence on the visual function of people with amblyopia is unknown. If DC polarization can improve vision in amblyopic eyes in adults, it would show that the visual cortex is still plastic, and it might help researchers develop a treatment for adults with amblyopia in the future.

Patients 18 years of age and older with amblyopia caused by crossing in or turning out of the eyes in childhood or by a difference in near- or farsightedness between the eyes may be eligible for this study. Candidates are screened with a medical history and complete eye examination, including a glaucoma screening and checks of vision, in- or out-turning of the eyes, depth perception, need for glasses, and the interior structures of the eyes.

Participants undergo two study sessions, scheduled at least 24 hours apart, involving the following procedures:

• Examination: Before each session, the patients' distance vision, contrast sensitivity (ability to see fading letters), and ability to read small print are checked in both eyes.
• DC polarization: Patients receive either 20 minutes of electrical stimulation or 20 minutes of sham stimulation (each patient will receive both electrical and sham stimulation on different days).
• Repeat examination: Immediately after the stimulation and again 20 minutes later, patients undergo repeat visual function testing. Those who show any differences in visual function 20 minutes after the stimulation are examined again 1 hour after the stimulation. Patients in whom the effect continues after 1 hour are examined again after 1 week.