Are they having you flush it with saline first? I had eye problems with my cham too and before I would medicate they had me flush it with saline and that would get his eyes open and then I'd put in the drops of medicine.
Whats wrong with the eye? Was this medicine prescribed by a vet?
If this was prescribed by a vet i cant believe he/she did not show you how to administer it before prescribing it for you to take home. If this is the case maybe go back to the vet and have them show you?