PEARLS FOR AMBLYOPIA DETECTION AND TREATMENT OF AMBLYOPIA AND STRABISMUS

In a keynote address delivered at the 2nd World Congress of Paediatric Ophthalmology and Strabismus, Emilio Campos MD, professor and chief of ophthalmology, University of Bologna, Italy, highlighted his career experiences and lessons learned during 40 years of clinical strabismology. His presentation provided pearls for amblyopia detection and treatment of amblyopia and strabismus. While screening in young children is critical to limit the burden of amblyopia-related visual impairment, achieving complete eradication of amblyopia through screening is impossible because of the presence of primary microstrabismus, noted Dr Campos.

In undertaking screening, evidence demonstrating there is good parallelism between free alternation of fixation and equal visual acuity in the two eyes until around age five indicates that fixation preference can be used for diagnosing and following amblyopia in children below the age when visual acuity can be reliably tested (<3 years). However, fixation preference in one eye can only be reversed by treatment early, said Dr Campos, cautioning that continuing occlusion after age five with the aim of obtaining free alternation has to be avoided.

“Intractable diplopia will be its only result,†he said. Cure of amblyopia is established by obtaining iso-acuity, free alternation, equal speed of reading and iso-accommodation. If residual amblyopia persists, hyperopic patients should receive a full cycloplegic correction to achieve their optimal acuity. Although a variety of modalities for treating amblyopia have been proposed over the years, Dr Campos said that none is a valid alternative to occlusion. Nevertheless, there is a place for medical therapy. Recognising the role of the dopaminergic system in amblyopia, Dr Campos and colleagues began investigating the use of citicoline. Their experience showed intramuscular injection of citicoline produced stable results for at least six months without complications.

“Citicoline represents a useful adjunct to part-time occlusion in non-responding patients, and with the current availability of an oral preparation, its use is easier and more accepted,†Dr Campos said. Research investigating botulinum toxin for strabismus treatment was initiated by Dr Campos almost three decades ago with a focus on essential infantile esotropia. “In the early 1970s, based on the idea that a prevalence of esotonus was the underlying aetiology, use of prisms and even surgery were proposed as treatment for infantile esotropia to break the system and induce an exotropia. However, injection of botulinum toxin into both medial rectus muscles is a more acceptable and less invasive approach,†he said.

The technique involves mask narcosis and injection of botulinum toxin A five units per muscle, under direct visualisation with an open sky approach. Dr Campos noted that stable results have been achieved in about 75 per cent of cases after just one treatment if the neurotoxin is administered no later than six months of age. “The end-result is usually a small-angle esotropia, rarely orthotropia, but normal binocular vision with stereopsis has never been achieved,†he said. Dr Campos provided four take-home messages about accommodative esotropia, the most common form of esotropia. Having found that hyperopes who develop esotropia have a reduced fusional amplitude in divergence, Dr Campos said that a full retinoscopic correction should be prescribed as prevention in these patients.

He addressed the misperception on hypo-accommodation in patients with a high accommodative convergence. Lack of accommodation is due to prolonged use of bifocals, noting that it pre-exists. Therefore, parents must be counselled that the need for near aid might remain after surgery. Dr Campos said that a change in the AC/A ratio probably underlies esophoria that is present with full correction in teenagers with accommodative esotropia and asthenopic complaints. In this situation, surgery can be performed but will eliminate only the phoric component.

Treatment of accommodative esotropia requires full retinoscopic correction and surgery is contraindicated. Bifocals should be used for the correction and not progressive lenses. Findings from studies by Dr Campos and colleagues also highlight issues to keep in mind when performing strabismus surgery. He cautioned colleagues to think about a lost or slipped muscle in patients who present with an excessive lid opening and a mild muscle action deficit so that they do not inadvertently operate on healthy muscles without fixing those responsible for the strabismus.

Dr Campos also underscored the need for follow-up within one week after reoperating on rectus muscles to evaluate patients for the development of corneal dellen, which occurs fairly frequently after reoperations. Noting a shift in strabismologists’ surgical activity to include more adults with acquired ocular motility problems, Dr Campos reinforced the need to evaluate motility in both eyes when operating on adult patients with a large deviation and severe motility disorder secondary to thyroid eye disease.

“The presence of a high degree hypotropia should not detract your attention from a careful evaluation of motility in the second eye and from CT/NMR examinations. Surgery on just one eye would not solve the problem,†he said. He further noted that involvement of the second eye can be delayed, occurring after a long period of the patient being diplopia-free. Awareness of this situation will allow proper diagnosis and intervention.

“The greatest mistake that a surgeon can make is to undo the previous surgery rather than approaching the newly affected eye,†Dr Campos said. Also pertaining to strabismus surgery in adults, Dr Campos noted misperceptions exist about the risk of diplopia after operating on a severely amblyopic eye of adults. Based on findings from his research showing that diplopia is much more likely to occur in amblyopic than in freely alternating patients, there is no risk of postoperative diplopia in adults with infantile alternating strabismus. However, greater caution is needed in deep amblyopic patients.