The eye behind the red lens only sees a target, while the eye behind the green lens only sees a target. The patient uses the glasses and looks at a picture with red and green objects to keep both eyes to work together as a team or unit.
Using the appropriate combination, conditions can be arranged so that the ‘weaker’ or lazy eye is the only eye capable of viewing the image, although both eyes are open and seeking input. The patient uses the glasses and looks at a picture with red and green objects. The red objects may be red and rich in detail, which will require more work on the part of the eye. Each eye sees a different target, so the patient gets important feedback about when he or she is suppressing the amblyopic eye.
Following feedback from the patient on which color the patient cannot see or reports this colored image has gone missing, we then know which eye is being ignored or suppressed. This suppression occurs in patients with amblyopia.