title: Pupil to limbus ratio: Introducing a simple objective measure using two-box method for measuring early anisocoria and progress of pupillary change in the ICU.
abstract: BACKGROUND
  Measurement of static pupillary size in the ICU is of importance in cases of acutely expanding intracranial mass lesions. The inaccuracies with subjective assessment of pupillary size by medical personnel preclude its use in emergent neurological situations.
  
  
  OBJECTIVE
  To determine if the ratio of pupil to limbus diameter (PLD ratio) measured by a two-box method is a reliable measure of pupil size for detecting early anisocoria and measuring pupillary changes.
  
  
  METHODS
  The PLD ratio was defined as the ratio of the pupillary diameter measured at a para-horizontal axial plane with the limbus diameter measured at the same or parallel axial plane. A two-box method was used to estimate the diameters of imaged pupils. Eyes were imaged using an iPhone 4S cellphone camera. Background illumination was measured and kept constant. The pupils of a 78-year-old woman, who presented with a large intra-axial parenchymal hemorrhage, were imaged. The patient had left pupillary miosis in dark but not in bright light. After presenting this case along with the images of the pupillary examination, a group of 21 medical staff were asked several questions on the pupillary examination. Reliability of PLD ratio were assessed via standard error of mean (S.E.M) of PLD ratios for 3 different subjects each imaged under constant illumination and fixation but from different angles to the optical axis.
  
  
  RESULTS
  Analysis of questionnaire data together with PLD ratios revealed that ~ 14% and 10% of participants could estimate the pupillary size in darkness and bright light respectively but none were simultaneously accurate indicating that subjective assessment of pupillary size was unreliable. The approach towards a systematic pupillary examination was inconsistent among the participants. The PLD ratio was found to be a reliable measure of pupillary size with standard error of mean below 0.1 mm for the three subjects tested.
  
  
  CONCLUSIONS
  Static pupillary sizes can be objectively and consistently evaluated using PLD ratios using a two-box method. PLD ratios are resistant, within limits, to changes in imaging angle or choice of para-horizontal axes for measurement.
authors.affiliation: Department of Neurology, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, USA.
authors.forename: Deb Kumar
authors.initials: DK
authors.lastname: Mojumder
authors.affiliation: Department of Neuroscience, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Saumil
authors.initials: S
authors.lastname: Patel
authors.affiliation: Department of Internal Medicine, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, USA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Nugent
authors.affiliation: Department of Neurology, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, USA.
authors.forename: John
authors.initials: J
authors.lastname: Detoledo
authors.affiliation: Department of Neurology, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, USA.
authors.forename: Jongyeol
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Radiology, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, USA.
authors.forename: Nabeel
authors.initials: N
authors.lastname: Dar
authors.affiliation: Department of Neurology, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, USA.
authors.forename: Henrik
authors.initials: H
authors.lastname: Wilms
keywords: Acute intra-cerebral mass lesion; anisocoria; intensive care unit; limbus; pupil; two-box method