title: Usability of prostaglandin monotherapy eye droppers.
abstract: OBJECTIVE
  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.
authors.affiliation: Ophthalmic Research Group, Life and Health Sciences, Aston University, Birmingham, UK.
authors.forename: Tom
authors.initials: T
authors.lastname: Drew
authors.affiliation: Ophthalmic Research Group, Life and Health Sciences, Aston University, Birmingham, UK.
authors.forename: James S
authors.initials: JS
authors.lastname: Wolffsohn
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D000959:Antihypertensive Agents / Q000008:administration & dosage*; D005260:Female; D005901:Glaucoma / Q000188:drug therapy*; D006801:Humans; D007322:Instillation, Drug; D000077338:Latanoprost; D008297:Male; D008875:Middle Aged; D009883:Ophthalmic Solutions / Q000008:administration & dosage*; D011312:Pressure; D011453:Prostaglandins / Q000008:administration & dosage*; D011461:Prostaglandins F, Synthetic / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D000959:Antihypertensive Agents; D009883:Ophthalmic Solutions; D011453:Prostaglandins; D011461:Prostaglandins F, Synthetic; D000077338:Latanoprost
keywords: Glaucoma; Treatment Medical