Sir,

I read with interest the report by Mitrut et al1 describing the changes in visual hallucinations after intravitreal injection of ranibizumab for neovascular age-related macular degeneration (AMD). The authors mention early in the article the term Charles Bonnet syndrome (CBS). I feel it is important to point out that not all of the visual experiences described in this series should be described with this term. CBS occurs in patients with poor vision secondary to various ophthalmic conditions, not just AMD,2, 3 and its definition includes the presence of formed, complex visual hallucinations.2, 3 Hence, colours, patches, spots, or lights may not be manifestations of CBS. In particular, the experiences of the two patients in group III who developed ‘hallucinations’ after the intravitreal injection could be explained by alternative mechanisms, such as visualization of the injected drug and vitreous traction on the retina following the injection. It would be interesting to know the time of onset of these phenomena and whether they persisted.

Regardless of whether the hallucinations constitute actual CBS, there are other interesting points that merit discussion. The authors do not mention a possible increase in intensity of visual hallucinations in Table 1, and it would be interesting to know whether this was investigated. It has been shown that visual hallucinations may increase in frequency or even begin for the first time following a change in the patient's ocular condition.4, 5 The dynamic change in visual acuity may be more important in precipitating hallucinations rather than the absolute visual acuity.4

One of the difficulties of describing the characteristics of hallucinations is their rarity, and it would be difficult to draw any definitive conclusions based on the small numbers in this series. Of the four patients in group II, only two experienced a decrease in intensity of the visual phenomenon. However, it has been shown that the frequency of visual hallucinations changes with time,4, 5 and may decrease or cease spontaneously.

I agree with the authors that this is an important symptom to enquire about, as patients are often reluctant to discuss their hallucinations.2, 3 A long-term study will be required, probably including a larger baseline population, in order to determine the course of hallucinations following intravitreal injections.