Lights On-Off Test

a.k.a. Small field central fusion test

• This test is useful in the setting of diplopia in the presence of a dragged fovea causing diplopia giving central-peripheral rivalry
• Use a single white letter on a black monitor about 20/70 in size
• Must have a very dark room and no light bleeding through an LCD monitor
• The patient sees diplopia when fixating on the letter with the lights on
• With the lights off, the diplopia resolves

from De Pool ME. et al. The Dragged-Fovea Diplopia Syndrome: Clinical Characteristics, Diagnosis and Treatment. Ophthalmology 2005;112:1455-1462