Dispensing eye drops from flexible plastic dropper bottles. Part III: Comparison between volunteers and elderly patients
The delivery of drops from flexible plastic dropper bottles by ten healthy volunteers was compared to that by six elderly patients aged 50 years or older. During the dispensing of the drops the air pressure inside the bottle, the weight of the drops and the time necessary to dispense a drop were registered. The influence of the flexibility of the dropper bottle and the design of the dropper tip was investigated. In general, the drop delivery data of the elderly patients were comparable to those of the healthy volunteers. However, the patients squeezed the dropper bottles fitted with a special design dropper tip less strongly as the volunteers, resulting in a lower air pressure difference, but a higher drop weight. For one subject, a patient with severe arthritis, dispensing drops from this special design dropper tip was at the limit of the capability to squeeze. Overall, the stiffness of the dropper bottle had no significant effect on the delivery of drops by the volunteers or the patients. On the other hand, the smaller the inner aperture diameter of the dropper tip, the larger the air pressure difference created inside the bottle and the longer the dispensing time.