The dragged-fovea diplopia syndrome

The dragged-fovea diplopia syndrome

David L. Guyton

The Krieger Children’s Eye Center at the Wilmer Institute, The Johns Hopkins University School of Medicine, Baltimore, MD, USA

Over the past 15 to 20 years, we have seen approximately 90 patients with smallangle, comitant diplopia, almost always with a small vertical component, which was impossible to correct with prism in the glasses. Typically, a small vertical prism relieves the diplopia momentarily, but the double vision returns in five to 20 seconds. The patient usually presents with a ‘bag-of-glasses syndrome’, unable to obtain a satisfactory pair of glasses to eliminate the diplopia.

These patients have all had one finding in common – retinal disease producing traction on the fovea. The Amsler grid examination was always abnormal in at least one eye. The cause of the diplopia quickly became apparent: the fovea in one eye was being dragged out of alignment with the fovea in the other eye, even though visual acuity often remained reasonably good. Peripheral fusion maintained single vision in the periphery, but central, foveal fusion was not strong enough to compete with peripheral fusion, and central double vision was the result! We have dubbed this syndrome the dragged-fovea diplopia syndrome.1

When a small prism was introduced to rid the patient of the central diplopia, the resulting peripheral diplopia stimulated peripheral fusion to realign the eyes, compensating for the prism, and central double vision returned. Some patients have been given more and more prism, actually causing true strabismus over time, secondary to adaptation to the increasing prism!

The most common cause of this problem is a parafoveal epiretinal membrane.2 Other causes are scars near the fovea, subretinal neovascular membranes causing foveal distortion,3 and a previously detached retina that reattached in a distorted manner.

This cause of the double vision should be suspected when:

•the misalignment is of a small-angle and comitant, usually with a small vertical component;

•prism has been tried before but has been unsuccessful; and

•there is a history of retinal disease, retina treatment, or practically any form of intraocular surgery.

Address for correspondence: David L. Guyton, MD, Wilmer Institute 233, Johns Hopkins Hospital, Baltimore, MD 21287-9028, USA. Email: dguyton@jhmi.edu

At the Crossings: Pediatric Ophthalmology and Strabismus, pp. 169–172

Proceedings of the 52nd Annual Symposium of the New Orleans Academy of Ophthalmology, New Orleans, LA, USA, February 14-16, 2003

edited by Robert J. Balkan, George S. Ellis Jr. and H. Sprague Eustis © 2004 Kugler Publications, The Hague, The Netherlands

Fig. 1a. A single white-on-black letter on a visual acuity monitor is seen double when the lights are on, stimulating peripheral fusion.

The diagnosis can definitely be confirmed by:

•finding an abnormality on Amsler grid testing in at least one eye;

•observing recurrence of the diplopia within five to 20 seconds after initial neutralization with a small prism;

•observing central fusion of a small white letter against a black background when the room lights are turned off entirely (Fig. 1b), with recurrence of the central double vision when the room lights are turned on again (Fig. 1a). We call this the smallfield central fusion test, or simply the lights on-off test; and

•observation of a scar or epiretinal membrane in or near the fovea of one eye on careful slit-lamp fundus examination.

Treatment of the dragged-fovea diplopia syndrome by prisms or by eye muscle surgery is absolutely futile. Vision is good enough that retinal surgery is usually contraindicated because of the risks involved. Even when epiretinal membranes can be peeled, the distortion they have caused does not often disappear.

Occasionally we can be lucky enough to be able to convert the patient to monovision, either with contact lenses or occasionally with glasses, so that one eye is used for distance and the other for near. However, the optical difference between the two eyes with monovision is not usually enough for the patient to be able to ignore the central double vision.

Fig. 1b. When the room lights are totally turned off, extinguishing the stimuli for peripheral fusion, the central white letter is fused and seen as single within a few seconds, by the unopposed operation of ‘central’ fusion.

Occlusion of one eye may be the best option. This is best done with partial occlusion, using a vertical strip of three-quarter-inch wide Scotch ‘Satin’® tape placed on the rear surface of the glasses before the non-preferred eye. This is a new type of Scotch tape that is finely translucent, enough to block the patient’s central vision, but clear enough for others to see the patient’s eye through the tape. In other words, it is cosmetically much more acceptable than a black patch, and much less obvious than most other types of tape.

Patients with the dragged-fovea diplopia syndrome are always distraught to learn that the underlying problem cannot be corrected, but at least they are happy to finally learn the cause. They are also very appreciative when shown the benefits of partial occlusion. The Scotch Satin tape does interfere with depth perception, but this is usually a small price to pay to be rid of the central diplopia.

References

1.De Pool ME, Broome S, Guyton DL: The dragged-fovea diplopia (DFD) syndrome. (In preparation)

2.Bixenman WW, Joffe L: Binocular diplopia associated with retinal wrinkling. J Pediatr Ophthalmol Strabismus 21:215-219, 1984

3.Burgess C, Roper-Hall G, Burde R: Binocular diplopia associated with subretinal neovascular membranes. Arch Ophthalmol 98:311-317, 1980