title: VARIABILITY IN FOVEAL AVASCULAR ZONE AND CAPILLARY DENSITY USING OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY MACHINES IN HEALTHY EYES.
abstract: OBJECTIVE
  To evaluate the variability in foveal avascular zone (FAZ) and capillary density measurements on optical coherence tomography angiography using Optovue RTVue XR Avanti (OA) (Optovue) and Zeiss Cirrus HD-OCT 5000 (ZC) (Carl Zeiss Meditec).
  
  
  METHODS
  In this prospective, comparative case series, parafoveal (3 × 3 mm) optical coherence tomography angiography scans were obtained on healthy volunteers using both the Avanti and Cirrus. The FAZ area and capillary density at the level of both the superficial and deep capillary plexus were measured automatically using the built-in ReVue software (Optovue) with the Avanti as well as manually using ImageJ (National Institutes of Health) with both machines.
  
  
  RESULTS
  There were 50 eyes in 25 healthy volunteers included in the analysis. Mean subject age was 33 years and there were 14 women (56%). On optical coherence tomography, mean central macular thickness was significantly greater on OA (259.1 μm) than ZC (257.6 μm, P = 0.0228). On optical coherence tomography angiography, mean superficial and deep plexus FAZ measured 0.2855 mm and 0.3465 mm on Avanti automated (A-A), 0.2739 mm and 0.3637 mm on Avanti manual (A-M), and 0.2657 mm and 0.3993 mm on Cirrus manual (C-M), respectively. There were no statistically significant differences in superficial plexus FAZ measurements between the A-A and A-M (P = 0.4019) or A-A and C-M (P = 0.1336). The A-M measured significantly larger than C-M (P = 0.0396). Deep plexus FAZ measurements were similar on A-A and A-M (P = 0.6299), but both were significantly less compared with C-M (P < 0.0001 for A-A vs. C-M, P = 0.0184 for A-M vs. C-M). Mean superficial and deep plexus capillary densities were 53.6% and 59.3% on A-A, 48.1% and 47.7% on A-M, and 52.5% and 48.1% on C-M, respectively. Superficial plexus capillary density measurements were statistically similar on A-A and C-M (P = 0.0623), but both were significantly higher than A-M (P < 0.0001 for A-A vs. A-M, P < 0.0001 for A-M vs. C-M). However, deep plexus capillary density measurements on A-A were significantly higher than A-M (P < 0.0001) and C-M (P < 0.0001), but A-M and C-M measurements were similar (P = 0.5986). There was no significant difference in all parameters measured in both eyes of one subject using any of the three measuring techniques.
  
  
  CONCLUSIONS
  While measurements taken with the same machine and technique are consistent and reliable between fellow eyes, significant variability exists in FAZ and capillary density measurements among different machines and techniques. Comparison of measurements across machines and techniques should be considered with caution.
authors.affiliation: Ocular Oncology Service, Wills Eye Hospital, Thomas Jefferson University, Philadelphia, Pennsylvania.
authors.forename: George N
authors.initials: GN
authors.lastname: Magrath
authors.forename: Emil Anthony T
authors.initials: EAT
authors.lastname: Say
authors.forename: Kareem
authors.initials: K
authors.lastname: Sioufi
authors.forename: Sandor
authors.initials: S
authors.lastname: Ferenczy
authors.forename: Wasim A
authors.initials: WA
authors.lastname: Samara
authors.forename: Carol L
authors.initials: CL
authors.lastname: Shields
mesh_terms: D000328:Adult; D002196:Capillaries / Q000473:pathology; D004867:Equipment Design; D005260:Female; D005451:Fluorescein Angiography / Q000295:instrumentation*; D005584:Fovea Centralis / Q000098:blood supply*; D005654:Fundus Oculi; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000473:pathology*; D041623:Tomography, Optical Coherence / Q000295:instrumentation*; D055815:Young Adult