title: The effect of needle gauge, needle type, and needle orientation on the volume of a drop.
abstract: OBJECTIVE
  The purpose of this study was to determine impact of needle gauge, type, and orientation on average volume of drop dispensed.
  
  
  METHODS
  Five needle gauges (22G, 23G, 25G, 27G, and 30G) were examined. For each gauge, volume of drop delivered was determined for standard sharp beveled tip, blunt tip, and after breaking off of the sharp needle from the hub. Vertical and horizontal orientation of the needle was tested for effect on drop volume for 22-G and 30-G sharp beveled needles.
  
  
  RESULTS
  Mean drop volume was affected by needle gauge, needle orientation, and whether the needle had been broken off from its hub. Mean drop volume scaled directly with needle diameter with drop volumes of 25.0 μL (±20.2) and 83.9 μL (±16.5) being found for 30-gauge and 22-gauge needles, respectively. Intermediate gauges (27, 25, 23G) yielded intermediate drop volumes. Blunt needles tended to produce larger drop volumes compared to sharp beveled needles, but these differences did not reach statistical significance. Breaking off of the needle from the hub produced substantially larger drop volumes with little difference being found between needle gauges. Average volumes of 1 drop from a 22-G vertical, 22-G horizontal, 30-G vertical, and 30-G horizontal sharp beveled needle were 20.2, 9.1, 10.1, and 3.3 μL, respectively.
  
  
  CONCLUSIONS
  These findings have relevance for controlled delivery of topical ophthalmic medications to patients.
authors: Department of Surgical and Radiological Sciences, University of California Davis, Davis, CA, 95616, USA.
authors: Geneva K
authors: GK
authors: Tripp
authors: Department of Surgical and Radiological Sciences, University of California Davis, Davis, CA, 95616, USA.
authors: Kathryn L
authors: KL
authors: Good
authors: Department of Surgical and Radiological Sciences, University of California Davis, Davis, CA, 95616, USA.
authors: Monica J
authors: MJ
authors: Motta
authors: Department of Population Health and Reproduction, University of California Davis, Davis, CA, 95616, USA.
authors: Philip H
authors: PH
authors: Kass
authors: Department of Surgical and Radiological Sciences, University of California Davis, Davis, CA, 95616, USA.|Department of Ophthalmology and Vision Science, School of Medicine, University of California Davis, Davis, CA, 95616, USA.
authors: Christopher J
authors: CJ
authors: Murphy
mesh_terms: D000818:Animals; D009339:Needles; D009883:Ophthalmic Solutions / Q000008:administration & dosage*; D014730:Veterinary Medicine
chemical_list: D009883:Ophthalmic Solutions
keywords: drop volume; eye drop; needle gauge; needle orientation; needle size; topical therapy