Clinical Trial: Visual Cortex Stimulation in Patients With Amblyopia

Study Status: Completed
Recruit Status: Completed
Study Type: Interventional

Official Title: Investigation of Visual Plasticity by a Direct Current Stimulation of Occipital Cortex in Adult Amblyopia

Brief Summary:

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' dista
  

  Detailed Summary:

  Background: Amblyopia is a disorder of reduced visual function in an eye, without ocular disease, which arises as a result of an abnormal visual experience in early life. It is attributed to a cortical suppression of the image from the amblyopic eye caused by blur or diplopia. Amblyopia is the leading cause of preventable monocular vision loss in the US affecting 2% to 5% of the population. In addition to significant visual deficits, amblyopes are more likely to loose sight in the other, healthy eye as a result of accidents or ocular diseases. Accepted treatment of amblyopia, which includes patching or pharmacological, or optical penalization of the fellow eye, is limited to young children. This treatment is considered ineffective beyond 8 years of age, and no treatment is offered to older individuals, who comprise 72% of the population of amblyopes.

  Recent evidence suggests that some cortical plasticity might be present in older individuals beyond the accepted age limit for the amblyopia treatment. Spontaneous improvement of visual acuity in the amblyopic eye was reported in some adults, who lost sight in the good eye following trauma or disease. However, the chance of spontaneous improvement of visual acuity to a usable level is relatively low. Therefore, it is important to search for modalities to improve the vision in amblyopic individuals to prevent incapacitating loss of function following loss of sight in a sound eye.

  Weak direct current (DC) stimulation is a noninvasive method able to induce cortical excitability changes. It has been previously safely applied in many animal and several human studies, and was able to modulate activity of primary motor and prefrontal cortices. These studies revealed that cathodal stimulation reduces spontaneous firing rates of cortical cells, most likely by hyperpolarizing cortical n
  Sponsor: National Eye Institute (NEI)
  

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  Information By: National Institutes of Health Clinical Center (CC)
  

  Dates:
  Date Received: November 17, 2004
  Date Started: November 2004
  Date Completion: June 2006
  Last Updated: June 23, 2006
  Last Verified: June 2006