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Cyclic strabismus is a rare phenomenon characterised by recurring periods of heterotropia usually on alternate days. It was first described by Bohm in 18451 and classically follows a 48 hour cycle with 24 hours of “straight” eyes followed by 24 hours of manifest strabismus. It usually appears spontaneously although it has been reported in the aftermath of cataract, retinal detachment, and intracranial surgery.2–4 In addition there are two case reports of cyclical esotropia developing following strabismus surgery for intermittent exotropia5 and for infantile esotropia.6 However, there are no previous reports of this unusual condition developing after surgery for partially accommodative esotropia. We therefore present such a case.
A 14 year old girl was referred by her optometrist with an intermittent esotropia. Both the patient and her mother had noticed that the squint was present on some days but not on others, irrespective of spectacle wear. Six years previously she had undergone a left medial rectus recession of 5 mm and a left inferior oblique recession for a partially accommodative left esotropia with inferior oblique over action. Unfortunately there were no previous orthoptic measurements available. However, according to her parents her surgery was successful and she had been discharged from follow up. Subsequently, despite full time spectacle wear, there had been a gradual decrease in cosmesis to her present state. She had no other ocular or medical history of note. At the time of her most recent presentation her visual acuities were 6/6, N5 in both eyes and cycloplegic refraction was unchanged from the full prescription given by her optometrist (right+4.00/+0.50×135, left+4.00/+0.25×160). Orthoptic assessment revealed a fully accommodative left esotropia with right hyperphoria. There was normal retinal correspondence with sensory and motor fusion and stereo acuity was 55′ of arc (Frisby test). She was therefore advised to wear her glasses full time. On review two months later both the patient and her mother were adamant that the squint was present every second day, with that particular day being a “squinting day”, which correlated with the last clinic appointment being on a “non-squinting day”. She was found to have a partially accommodative left esotropia measuring with glasses 35 and 30 prism dioptres (Δ) for near and distance respectively and measuring without glasses 50Δ and 40Δ for near and distance respectively. In addition she had bilateral inferior oblique overaction. Sensory fusion showed left suppression. The history and clinical findings were suggestive of a diagnosis of cyclical esotropia. She was asked to start a diary documenting the presence or absence of her squint on a daily basis until her next visit 6 weeks later, which confirmed the cyclical nature of her strabismus. Because of forthcoming school examinations no surgical treatment was planned at this stage. On review a further 2 months later she felt her squint was present the majority of the time, with her eyes “straight” only every third or fourth day. Her orthoptic findings were unchanged. She was therefore listed for surgery and underwent right medial rectus recession of 5.5 mm, left medial rectus recession of 2.5 mm, and bilateral inferior oblique muscle recession. Postoperatively she had a fully accommodative left esotropia measuring 6Δ for near and distance with glasses, and 25Δ and 20Δ for near and distance respectively without glasses. There was constant binocular single vision with a stereo acuity of 40′ of arc (Frisby test). This has remained stable during a nine month follow up period.
The aetiology of this unusual form of strabismus is unknown although it has been reported in association with abnormalities of the central nervous system.7 However, our patient was otherwise fit and well with nothing to suggest an underlying neurological problem. According to von Noorden8 cyclical strabismus in childhood may last from 4 months to several years after which time it invariably becomes constant. Treatment in such patients is based upon the premise that they are basically strabismic but capable of good binocular vision. This would probably account for the reported success of surgery in these children,2 which is also our experience in this case. Although cyclical esotropia following strabismus surgery is a rare phenomenon, this report illustrates the importance of considering it in the differential diagnosis in those patients who have variable orthoptic findings, particularly as it is amenable to surgical management.