The paper examines the vacillation of the density of the foil lyophilised from hydrogel containing 40 g/l of hydroxypropylmethylcellulose (HPMC 4000). Lamellae of a diameter of 0.55 cm were formed to estimate the density of cm 2 of xerogel. In comparison with traditional regressive methods, the use of a two-dimensional correlogram is recommended. The most important finding is the achieve- ment of random vacillation of density in a distance of ca 2 cm in connection with stamping lamellae from the lyophilised foil. The findings make it possible to optimise the procedure of pouring hydrogel for lyophilisation with a subsequent decrease in density vacillation of lyophilised ophthalmic lamellae.

        Key words: lyophilisation – hydroxypropylmethylcellulose – xerogel – density – correlogram