AIM: To determine the force needed to extract a drop from a range of current prostaglandin monotherapy eye droppers and how this related to the comfortable and maximum pressure subjects could exert.
METHODS: The comfortable and maximum pressure subjects could apply to an eye dropper constructed around a set of cantilevered pressure sensors and mounted above their eye was assessed in 102 subjects (mean 51.2±18.7 years), repeated three times. A load cell amplifier, mounted on a stepper motor controlled linear slide, was constructed and calibrated to test the force required to extract the first three drops from 13 multidose or unidose latanoprost medication eye droppers.
RESULTS: The pressure that could be exerted on a dropper comfortably (25.9±17.7 Newtons, range 1.2-87.4) could be exceeded with effort (to 64.8±27.1 Newtons, range 19.9-157.8; F=19.045, p<0.001), and did not differ between repeats (F=0.609, p=0.545). Comfortable and maximum pressures exerted were correlated (r=0.618, p<0.001), neither were influenced strongly by age (r=0.138, p=0.168; r=-0.118, p=0237, respectively), but were lower in women than in men (F=12.757, p=0.001). The force required to expel a drop differed between dropper designs (F=22.528, p<0.001), ranging from 6.4 Newtons to 23.4 Newtons. The force needed to exert successive drops increased (F=36.373, p<0.001) and storing droppers in the fridge further increased the force required (F=7.987, p=0.009).
CONCLUSIONS: Prostaglandin monotherapy droppers for glaucoma treatment vary in their resistance to extract a drop and with some a drop could not be comfortably achieved by half the population, which may affect compliance and efficacy.
|Journal||British Journal of Ophthalmology|
|Early online date||11 Mar 2015|
|Publication status||Published - 2015|
Bibliographical noteThis article has been accepted for publication in British journal of ophthalmology following peer review. The definitive copyedited, typeset version Drew, T & Wolffsohn, JS 2015, 'Usability of prostaglandin monotherapy eye droppers' British journal of ophthalmology, Online first is available online at: www.http://bjo.bmj.com/content/early/2015/03/11/bjophthalmol-2014-306291
Funding: Laboratories Thea, France
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