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Thomas Edward Drew, James Stuart Wolffsohn; Usability of Glaucoma Medication Eye Droppers. Invest. Ophthalmol. Vis. Sci. 2014;55(13):536.
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To determine the force needed to extract a drop from a range of current glaucoma medication eye droppers and how this related to the comfortable and maximum pressure patients could exert.
The comfortable and maximum pressure patients could apply to an eye dropper [vial or unit-dose (UD)] constructed around a set of cantilevered pressure sensors (Richmond Industries, UK) and mounted above the patients eye was assessed in 40 patients aged 19-85 years repeated 3 times. A load cell amplifier (Richmond Industries, UK) mounted on a stepper motor controlled linear slide (Trinamic GmbH, Germany; Geckodrive Inc., USA) was constructed to test the force required to extract the first 6 drops from glaucoma medication eye dropper : 4 generics latanoprost (50 µg/ml) vials of 2.5 ml, preservative free bimatoprost (0.3mg/ml) 0.4 ml UD, preservative free tafluprost (15 µg/ml) 0.3ml UD, travoprost (0.004% 40 µg/mL) vial of 2.5 ml, latanoprost (0.005%) vial of 2.5ml, bimatoprost 0.1mg/ml vial of 3ml, bimatoprost 0.3mg/ml vial of 3ml and preservative free latanoprost (50µg/ml) 0.2ml UD.
The pressure that could be exerted on a dropper comfortably (30.8 ± 17.0 newtons, range 7.3 to 85.6) could be exceeded with effort (to 62.9 ± 25.6 newtons, range 33.2 to 130.9), but did not differ between repeats (ANOVA F = 2.178, p = 0.120). Comfortable and maximum pressure exerted were correlated (r = 0.769, p < 0.001), but neither were influenced strongly by age (r = 0.084, p = 0.605; r = -0.113, p = 0.489 respectively). The force needed to exert successive drops from each individual dropper design did not alter (F = 0.662, p = 0.447), but this did differ between dropper designs (F = 26.882, p < 0.001) with the force required ranging from 6.7 to 24.3 newtons. Preservative free latanoprost 50 µg/mL 0.2ml UD and latanoprost 0,005% vial of 2.5ml required significantly less force applied to exert a drop than the other eye droppers (p < 0.001).
Glaucoma medication droppers vary in their resistance to extract a drop and this could only be comfortably achieved by all patients with preservative free latanoprost 50 µg/mL 0.2ml UD and latanoprost 0,005% 2.5ml vial. Patients would struggle with other dropper designs and this may affect compliance and efficacy.
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