Double vision in one eye which persists after the other eye is covered

Monocular diplopia is double vision in one eye which persists after the other eye is covered. Image separation is slight, often described as 'ghosting.'

Common causes are:

• usually caused by abnormalities of the cornea, iris, lens, or vitreous or aqueous humour
  • for example:
    • refractive error - the commonest problem - if looking through a pinhole abolishes the diplopia then spectacles should be worn
    • developing cataract - areas of differing refractive index cause splitting of the light beam and diplopia. Usually abates as the opacification increases
    • corneal scarring

Reference:

1. Tan A. The two-minute approach to monocular diplopia. Malays Fam Physician. 2010 Dec 31;5(3):115-8.