Sir,

We report a case of comorbidity of exotropia with homonymous hemianopia in whom a careful preoperative assessment helped avoid an unexpected surgical outcome.

Case report

A 50-year-old male presented with a long-standing exotropia, requesting intervention for cosmetic purposes. He gave a history of an early-onset exotropia and amblyopia, with cosmetic strabismus surgery at the age of 20 years. Visual acuities were 6/6 OD and 6/12 OS. He described a consecutive exotropia within a year of surgery, which had remained stable since.

Examination revealed a concomitant exotropia, measuring 40 prism dioptres (PD) base in (BI) at 1/3 m and 35 PD BI at 6 m, with full motility. Ocular examination was unremarkable except for a left homonymous hemianopic field defect (Figure 1). Magnetic resonance imaging (MRI) scan of the brain confirmed an infarction in the right occipital lobe.

Figure 1
figure 1

Left homonymous hemianopia.

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A binocular driving visual field test resulted in a reasonably full field, presumably because the exotropia compensated for the hemianopia (Figure 2). Therefore, the patient declined surgery.

Figure 2
figure 2

Full binocular field.

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Comment

This case illustrates an important exception to the rule that two defects of the visual system usually lead to a more pronounced visual deficit than one.

Under binocular conditions, the functional significance of a homonymous hemianopia can be reduced by an exotropia of the ipsilateral eye (ie deviation in the direction of the field defect), resulting in panoramic vision. A prism correction of the exotropia, or botulinum toxin to realign the eye, followed by a repeat binocular visual field test helps predict the impact of a surgical correction of exotropia.

This combination is uncommon. Three reports of patients with exotropia who developed ipsilateral homonymous hemianopia concluded that strabismus correction is contraindicated in these patients in order to preserve their panoramic vision.1, 2, 3

This case report highlights the fact that hemianopias should be excluded before strabismus surgery. Reduction in visual field as a result of ‘cosmetic’ surgical alignment where there is an undetected hemianopia may have serious implications, including loss of driving license.