title: Can we predict which patients are at risk of having an ungradeable digital image for screening for diabetic retinopathy?
abstract: OBJECTIVE
  We aimed to determine the reasons for, and variables which predicted, ungradeable retinal photographs during screening patients for diabetic retinopathy.
  
  
  METHODS
  Age, duration of diabetes, visual acuity, and HbA1c were recorded. Following dark adaptation, a single 45 degrees nonmydriatic photograph was taken of each fundus. The pupils were then dilated and the photograph repeated. Using slit lamp biomicroscopy, lenticular changes (LOCS III), and fundus appearance were recorded.
  
  
  RESULTS
  In ungradeable photographs the fovea could not be visualised in 98% of cases of images from nonmydriatic photography, and in 88% if mydriasis was used. Poor definition in the nonmydriatic image was associated with a subsequent ungradeable mydriatic photograph (P=0.001), however, the positive predictive value was poor (34%). Age, posterior subcapsular cataract, and near vision predicted ungradeable status of nonmydriatic photographs (P<0.001, P=0.004, P=0.006, respectively; regression analysis). Nuclear colour and poor definition of the nonmydriatic photograph predicted ungradeable status of mydriatic photographs (P=0.006 & P=0.001, respectively).
  
  
  CONCLUSIONS
  Inability to visualise the fovea is the commonest cause of an ungradeable image from digital retinal photography. Age and posterior subcapsular cataract were best predictors of ungradeable status of nonmydriatic fundus photographs. Nuclear colour was the strongest predictor for ungradeable mydriatic photography.
authors.affiliation: Department of Ophthalmology, Ninewells Hospital and Medical School, Dundee, UK.
authors.forename: H
authors.initials: H
authors.lastname: Murgatroyd
authors.forename: A
authors.initials: A
authors.lastname: Cox
authors.forename: A
authors.initials: A
authors.lastname: Ellingford
authors.forename: J D
authors.initials: JD
authors.lastname: Ellis
authors.forename: C J
authors.initials: CJ
authors.lastname: Macewen
authors.forename: G P
authors.initials: GP
authors.lastname: Leese
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003930:Diabetic Retinopathy / Q000175:diagnosis*; D005123:Eye / Q000187:drug effects; D005260:Female; D005584:Fovea Centralis / Q000187:drug effects; D005654:Fundus Oculi; D006801:Humans; D008297:Male; D008875:Middle Aged; D009184:Mydriatics / Q000008:administration & dosage; D010781:Photography / Q000592:standards*; D011680:Pupil / Q000187:drug effects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D015351:Vision Screening / Q000379:methods
chemical_list: D009184:Mydriatics