Sir,

It was interesting to read the article by Gupta et al1 reporting the use of trans-scleral vision blue (TSVB). As the authors state, this is an off-label use and as such there should be good evidence to support its use or a robust audit to determine its efficacy. They reported that ‘there was no evidence of complications as a result of TSVB injection’; how did the authors look for such complications? Fourier domain optical coherence tomography (OCT) may be used to evaluate the photoreceptor inner–outer segment junction that has been shown to be disrupted when exposed to subretinal VB.2 Similarly, microperimetry and fundus autofluorescence may be useful.

The inner retina has evolved to be naturally isolated from direct contact with contents of the vitreous and blood. When this selective permeability is disrupted, as it occurs in many pathological situations, the presence of relatively ‘harmless’ endogenous fluids may result in damage. There should therefore be strong reasons before iatrogenically disrupting this balance, as the RPE and photoreceptors may be insulted either directly, by exposure to toxic agents, or indirectly, via non-iso-osmolar solutions. The authors cite Veckeneer et al3 stating ‘At 0.06% Trypan blue (TB) was concluded to be harmless’. In these experiments, however, the dye injection was intravitreal and should not be extrapolated to confirm safety if placed in the subretinal space. A further in vitro model tested the toxicity of 0.15% TB (higher than used here) in RPE cells and reported its safety.4 Subsequent in vivo experiments with subretinal 0.15% TB injections in rabbits showed significant photoreceptor and RPE damage.2 Even the injection of an iso-osmolar balanced salt solution has been shown to cause mild photoreceptor outer-segment damage.2

One important, and perhaps overlooked, finding of this study may be the increased occurrence of occult breaks around areas of prior retinal cryopexy. This could be used to strengthen the argument favouring laser retinopexy over cryopexy, but more importantly highlights that this is an area where we ought to be extra vigilant in our search for breaks when performing repeat surgery.