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Dyes and stains Part 1 – Lissamine green
June 29, 2018 - Sarah Farrant on Optician (UK) journal
Have you ever wondered why mushy peas or your favourite mint sauce is so green? It may be because they added Green S food dye (E number E142), which you may recognise as lissamine green.
This vital stain was introduced in 1973 by Norn 1 as an alternative to rose bengal for assessing the ocular surface. The TFOS DEWS II Report 2 recommends that lissamine green (along with Fluorescein assessment) should be used when evaluating ocular surface damage. Using both stains is the most appropriate diagnostic technique for evaluating ocular surface damage and that the benefits of using lissamine green outweighed any risks.
However, lissamine green appears to be underutilised in routine optometric practice and there are a number of potential reasons for this:
Lack of understanding
Belief that use of Fluorescein is sufficient
Making decisions based on other clinical findings or reported symptoms
Cost and time commitments
Supply issues
Confusion over the legal status
This article highlights the merits of lissamine green, along with best practice guidance on when, why and how it should be used.
What is lissamine green and how does it compare to the other dyes used for vital staining?
Lissamine green is an organic dye that is synthetically produced and its molecular weight is 576.6 Daltons. Since 1923, the Biological Stain Commission (BSC) has classified dyes with similar chemical structures according to their chromophores. Lissamine green is a diphenyl-naphthyl methane derivative of the phenylmethane dye, whereas fluorescein and rose bengal fall into the category of xanthine dyes. Despite rose bengal being a derivative of fluorescein, the clinical staining patterns of lissammine green and rose bengal are the most similar, though lissamine green does not fluoresce. Unlike rose bengal which causes ocular irritation, lissamine green is well tolerated making it the preferred choice in optometric practice.
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