MUC5AC and hyperinsulinemic hypoglycemia, familial, 4: Given that poor tear film stability is associated with reduction in goblet cell density and mucin deficiency on the ocular surface23, our results of conjunctival impression cytology and immunofluorescence staining for MUC5AC (Fig. 8) validate the findings of rose bengal staining (Fig. 5) and Schirmer test (Fig. 6).