á751ñMETAL PARTICLES IN OPHTHALMIC OINTMENTS
The following test is designed to limit to a level considered to be unobjectionable the number and size of discrete metal particles that may occur in ophthalmic ointments.
Procedure— Extrude,as completely as practicable,the contents of 10tubes individually into separate,clear,flat-bottom,60-mm Petri dishes that are free from scratches.Cover the dishes,and heat at 85
for 2hours,increasing the temperature slightly if necessary to ensure that a fully fluid state is obtained.Taking precautions against disturbing the melted sample,allow each to cool to room temperature and to solidify.
Remove the covers,and invert each Petri dish on the stage of a suitable microscope adjusted to furnish 30times magnification and equipped with an eye-piece micrometer disk that has been calibrated at the magnification being used.In addition to the usual source of light,direct an illuminator from above the ointment at a 45angle.Examine the entire bottom of the Petri dish for metal particles.Varying the intensity of the illuminator from above allows such metal particles to be recognized by their characteristic reflection of light.
angle.Examine the entire bottom of the Petri dish for metal particles.Varying the intensity of the illuminator from above allows such metal particles to be recognized by their characteristic reflection of light.Count the number of metal particles that are 50µm or larger in any dimension:the requirements are met if the total number of such particles in all 10tubes does not exceed 50,and if not more than 1tube is found to contain more than 8such particles.If these results are not obtained,repeat the test on 20additional tubes:the requirements are met if the total number of metal particles that are 50µm or larger in any dimension does not exceed 150in all 30tubes tested,and if not more than 3of the tubes are found to contain more than 8such particles each.