An investigation into the causes of non-compliance by patients using eyedrops has been undertaken by questionnaire, ability tests, and by tests on eyedrop bottles. The results indicate a high prevalence of non-compliance, compounded by an inability adequately to instill a drop into the eye. About half the patients had difficulty aiming the drop, and other problems including squeezing the bottle, blinking, and seeing the tip of the bottle. Ability tests included a measurement of the grip strength of patients to complement measurement of the force required to expel a drop from a bottle. Some patients, particularly those with arthritis, could not generate enough force to squeeze a bottle. These same patients also had difficulty with the other movements required to administer drops. While some attempts have been made to produce devices to assist with eyedrops which can improve the aim of the patient, none give assistance in expelling a drop. An additional problem found was the reluctance of patients to admit to medical staff that they experienced any difficulty with their drops.