Dear Editor,

The paper by El Mallah, et al. [1], reporting visual recovery in the amblyopes after visual loss in the non-amblyopic eye brings new evidence for visual system plasticity extending beyond what was considered the critical period. Our observation of two patients presented below further supports it and suggests plasticity may be pharmacologically enhanced.

A 22-year-old woman with strabismic amblyopia in the right eye (visual acuity 0.7) developed left optic neuritis with loss of acuity from 1.0 to 0.2. She received methylprednisolone 1 g/day i.v. for 3 days. Acuity improved over 2 weeks to 1.0 right (amblyopic) eye and to 0.8 in the left eye. The improvement was sustained over 2 years of observation. She subsequently developed definite multiple sclerosis (MS). The second patient was a 19-year-old woman with strabismic amblyopia in the right eye (visual acuity 0.2), and MS since age 8, with aggressive course after age 15. Frequent relapses, mainly myelopathic and cerebellar, responded to steroids. She had 3 days of i.v. steroids for a myelopathic relapse, and recovered. One month later she developed left optic neuritis (acuity 0.2). She noted an improvement in acuity (to 0.4) in the right eye. She received i.v. methylprednisolone for 3 days. Four weeks later, visual acuity had improved to 1.0 in the right eye but only to 0.3 in the left eye. A repeat course of steroids led to marginal further improvement in the left eye. The amblyopic eye recovery was sustained for over 18 months of follow-up.

These cases show that improvement in amblyopia can occur after optic neuritis in the fellow eye. The significant improvement may reflect the patients' younger ages, but also raises the fascinating possibility that pharmacological modulation with steroids may enhance or prolong the recovery effect. Other agents enhancing plasticity improve adult amblyopia [2], and steroids, which affect neural plasticity [3], may be a future consideration.

CS Constantinescu

I Gottlob
Leicester Royal Infirmary
Leicester LE2 7LX, UK

REFERENCES

(1) El Mallah MK, Chakravarthy U, Hart PM. Amblyopia: is visual loss permanent? Br J Ophthalmol 2000;84:952-956.
(2) Gottlob I, Stangler-Zuschrott E. Effect of levodopa on contrast sensitivity and scotomas in human amblyopia. Invest Ophthalmol Vis Sci 1990;31:776-780.
(3) Cameron SA, Dutia MB. Lesion-induced plasticity in rat vestibular nucleus neurones-dependent on glucocorticoid receptor activation. J Physiol (Lond) 1999;518:151-158