title: Effect of grid decentration on macular thickness measurements in normal subjects and patients with diabetic macular edema.
abstract: OBJECTIVE
  To evaluate the effect of optical coherence tomography (OCT) grid decentration on macular thickness measurements in healthy subjects and patients with diabetic macular edema.
  
  
  METHODS
  In this prospective study, 3D spectral-domain OCT images of 51 eyes with clinically significant diabetic macular edema and 29 healthy eyes were assessed. In each eye, the macular Early Treatment Diabetic Retinopathy Study grid was evaluated for decentration. After grid adjustment, changes in central subfield thickness (CST) and central subfield volume (CSV) measurements were recorded. Changes &gt;1 μm and &gt;8.5 μm in CST were considered as grid decentration and clinically significant grid decentration, respectively.
  
  
  RESULTS
  Grid decentration was found in 10 normal eyes (34.6%) and 32 clinically significant macular edema (CSME) eyes (62.7%, p = 0.01). Clinically significant CST changes were found in 3 normal eyes (10.3%) and 23 CSME eyes (45%, p = 0.001). The mean change in CST after grid adjustment was 6.4 ± 5.8 µm and 24.7 ± 27 µm in normal and CSME eyes (p = 0.04). Age, sex, and CST had no statistically significant effect on grid decentration in normal and CSME eyes. Best-corrected visual acuity was significantly worse in eyes with grid decentration (0.75 ± 0.55 vs 0.42 ± 0.22 logMAR, p = 0.02) and clinically significant grid decentration (0.81 ± 0.6 vs 0.45 ± 0.27 logMAR, p = 0.01). Change in CSV was detected in 3 normal eyes (10.3%) and 24 CSME eyes (47%, p = 0.001).
  
  
  CONCLUSIONS
  Grid decentration occurs in a large number of OCT thickness maps and leads to significant error in macular thickness measurements. The effect is more prominent in patients with CSME.
authors.affiliation: Eye Research Center, Rassoul Akram Hospital, Iran University of Medical Sciences, Tehran - Iran.
authors.forename: Khalil Ghasemi
authors.initials: KG
authors.lastname: Falavarjani
authors.forename: Joobin
authors.initials: J
authors.lastname: Khadamy
authors.forename: Hamid
authors.initials: H
authors.lastname: Safi
authors.forename: Nasser
authors.initials: N
authors.lastname: Karimi
authors.forename: Foad
authors.initials: F
authors.lastname: Amirkourjani
mesh_terms: D000328:Adult; D000368:Aged; D003930:Diabetic Retinopathy / Q000175:diagnosis*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D021621:Imaging, Three-Dimensional; D008266:Macula Lutea / Q000473:pathology*; D008269:Macular Edema / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D009929:Organ Size; D011446:Prospective Studies; D041623:Tomography, Optical Coherence / Q000379:methods; D014792:Visual Acuity