title: Crowdsourcing as a screening tool to detect clinical features of glaucomatous optic neuropathy from digital photography.
abstract: OBJECTIVE
  Crowdsourcing is the process of simplifying and outsourcing numerous tasks to many untrained individuals. Our aim was to assess the performance and repeatability of crowdsourcing in the classification of normal and glaucomatous discs from optic disc images.
  
  
  METHODS
  Optic disc images (N = 127) with pre-determined disease status were selected by consensus agreement from grading experts from a large cohort study. After reading brief illustrative instructions, we requested that knowledge workers (KWs) from a crowdsourcing platform (Amazon MTurk) classified each image as normal or abnormal. Each image was classified 20 times by different KWs. Two study designs were examined to assess the effect of varying KW experience and both study designs were conducted twice for consistency. Performance was assessed by comparing the sensitivity, specificity and area under the receiver operating characteristic curve (AUC).
  
  
  RESULTS
  Overall, 2,540 classifications were received in under 24 hours at minimal cost. The sensitivity ranged between 83-88% across both trials and study designs, however the specificity was poor, ranging between 35-43%. In trial 1, the highest AUC (95%CI) was 0.64(0.62-0.66) and in trial 2 it was 0.63(0.61-0.65). There were no significant differences between study design or trials conducted.
  
  
  CONCLUSIONS
  Crowdsourcing represents a cost-effective method of image analysis which demonstrates good repeatability and a high sensitivity. Optimisation of variables such as reward schemes, mode of image presentation, expanded response options and incorporation of training modules should be examined to determine their effect on the accuracy and reliability of this technique in retinal image analysis.
authors.affiliation: NIHR Biomedical Research Centre, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Danny
authors.initials: D
authors.lastname: Mitry
authors.affiliation: NIHR Biomedical Research Centre, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Tunde
authors.initials: T
authors.lastname: Peto
authors.affiliation: Department of Public Health and Primary Care, University of Cambridge, Strangeways Research Laboratory, Cambridge, United Kingdom.
authors.forename: Shabina
authors.initials: S
authors.lastname: Hayat
authors.affiliation: NIHR Biomedical Research Centre, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Peter
authors.initials: P
authors.lastname: Blows
authors.affiliation: School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.
authors.forename: James
authors.initials: J
authors.lastname: Morgan
authors.affiliation: Department of Clinical Gerontology, Addenbrookes Hospital, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Kay-Tee
authors.initials: KT
authors.lastname: Khaw
authors.affiliation: NIHR Biomedical Research Centre, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, United Kingdom.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Foster
mesh_terms: D063045:Crowdsourcing; D005901:Glaucoma / Q000150:complications*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008403:Mass Screening; D009898:Optic Disk / Q000473:pathology; D009901:Optic Nerve Diseases / Q000150:complications* / Q000175:diagnosis* / Q000473:pathology; D010781:Photography