In contrast to years past, especially from 2006 to 2009, where 'corneal staining' at two hours was a hot topic, there was almost no talk regarding the Andrasko grid.1 This is due to new compelling research that showed fluorescein is able to enter healthy, dividing cells2 and the signal seen with MPS solutions (PATH) is reversible and benign3-5 and occurs with all solutions, depending upon when viewed after lens insertion.1,6,7
What is more interesting is that the preservative polyquaternium-1 (Polyquad/PQ-1), which is found in several MPSs that show low levels of PATH at two hours, disrupts corneal cell membrane models at 7-8ppm; levels near (3ppm in RevitaLens OcuTec; AMO) or below (10ppm in Opti-Free Express and RepleniSH; Alcon) that found in three marketed solutions.3 This is in contrast to polyhexamethylene biguanide (PHMB), a preservative found in several of the solutions showing high levels of PATH at two hours, which had no effect on the same corneal cell membrane models up to 100 times that found in marketed solutions.
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