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Introduction
Intractable diplopia is a condition where binocular diplopia can only be eliminated via a means of occluding one eye. It can occur in patients with strabismus where binocular vision is absent and the ability to suppress is lost, either due to a change in alignment following botulinum toxin or surgery 1 2 or via reduction in the density of suppression following amblyopia treatment. 3 Intractable diplopia can also present following cataract surgery where once the vision is restored, diplopia is perceived due to inability to fuse the images. 4 5 Other potential causes are loss of fusion following severe head trauma and brain lesions or due to incompatibility of images after refractive surgery. The very nature of intractable diplopia means that it cannot be eliminated by surgical realignment of the eyes or correcting the angle with prisms and therefore presents important quality of life issues for the individuals affected. Elimination of the diplopic image can only be achieved by occluding one of the eyes. A variety of methods have been employed such as using occlusive contact lenses, Bangerter filters, opaque tape applied to glasses, induction of ptosis via botulinum toxin, corneal tattooing and opaque intraocular lenses (IOLs). 1 6-9 These methods are often poorly tolerated, may cause irritation and headaches, can be cosmetically poor or lead to corneal epitheliopathy or ulcers. At best the diplopia is resolved, but by virtue of the treatment, the patient is effectively left with only one functioning eye.
While it is clear that intractable diplopia would be a serious debilitating condition 10 11 for those affected, little is known regarding the incidence or presentation. It is reported to be a rare occurrence, but to date there has been no prospective study of intractable diplopia. Previous studies have either reported case reports, or retrospectively provided estimates of intractable diplopia resulting from the individual treatments of adult strabismus surgery (0.8%), 2 cataract surgery (accounting for 4.6% of patients who reported postoperative diplopia) 4 or amblyopia treatment (estimated five cases per year in the UK). 3 Knowledge of the incidence and presentation of intractable diplopia will provide a valuable base on which strategies to prevent its occurrence can be established. Additional information about how the patients with intractable diplopia are managed and...