Re: Putting vital stains in context

EDITOR: We note the recent article by Efron, in which considerable space is given to solution-induced corneal staining (SICS) and preservative-associated transient hyperfluorescence (PATH). In his concluding comments, Professor Efron makes the assertion ‘I feel that this phenomenon (that is, SICS) can be largely explained by PATH’. While commending this otherwise excellent review, we feel that this particular conclusion is premature, as it discounts two pieces of relevant information, both of which will be familiar to those who work with fluorescein under these circumstances. First, it is a commonly remarked-upon fact, as well as the subject of a recent report, that the epithelial appearance corresponding to SICS can be observed without the instillation of fluorescein. The PATH hypothesis is that preservatives released from soft contact lenses interact with fluorescein and the ocular surface giving the appearance of staining. It seems evident that removing fluorescein molecules from the system should eliminate all signs of PATH. Second, the PATH hypothesis has not been able to explain the punctate nature of the staining pattern observed in SICS. Given that preservative molecules in multipurpose solutions are at least 10,000 times smaller than corneal epithelial cells, the mechanism implied by PATH would be expected to produce a uniform distribution of the preservative and associated fluorescein molecules across the cornea. Consequently, the fluorescent appearance should also be uniform, rather than the discrete punctate spots, often in an annular pattern, that actually occur. To date, PATH has been founded on theory and an in vitro model that uses liposomes rather than corneal epithelial cells. We suggest that acceptance of the PATH theory requires that it must also be consistent with readily observable phenomena, such as those described above. Unless and until that is the case, while remaining an interesting hypothesis to explain the observation seen when certain contact lens solutions and materials are used synergistically, it cannot be seen as proven.