Influence of correction of ocular magnification on spectral-domain OCT retinal nerve fiber layer measurement variability and performance.
OBJECTIVE
To analyze the influence of ocular magnification on the peripapillary retinal nerve fiber layer (RNFL) thickness measurement and its performance as acquired with spectral-domain optical coherence tomography (SD-OCT).


METHODS
Spectral domain OCT measurements from 108 normal eyes (59 subjects) and 72 glaucoma eyes (58 patients) were exported and custom software was used to correct RNFL measurements for ocular magnification. Retinal nerve fiber layer prediction limits in normal subjects, structure-function relationships, and RNFL performance for detection of glaucoma were compared before and after correction for ocular magnification (Bennett's formula). Association of disc area with cross-sectional RNFL area was explored.


RESULTS
The median (interquartile range, [IQR]) visual field mean deviation and scaling factor were 0 (-0.85 to 0.73) dB and 0.96 (0.93-1.00) in normal eyes and -4.0 (-6.0 to -2.2) dB and 0.99 (0.95-1.03) in the glaucoma group (P < 0.001 and P = 0.003, respectively; average correction 3%). Correction for ocular magnification caused a reversal of the negative relationship between the cross-sectional RNFL area and axial length (slope = -0.022 mm(2)/mm, P = 0.015 vs. = 0.22 mm(2)/mm, P = 0.007). However, such correction did not change RNFL prediction limits (except in superior and nasal quadrants), improve global or regional structure-function relationships, or enhance the ability of RNFL measurements to discriminate glaucoma from normal eyes (P > 0.05). The cross-sectional RNFL area was not correlated with optic disc area (P = 0.325).


CONCLUSIONS
Correction of RNFL measurements for ocular magnification did not improve prediction limits in normal subjects or enhance the performance of SD-OCT in this group of eyes in which the axial length did not deviate significantly from average values. The cross-sectional area of the RNFL was not related to the optic disc area.
Glaucoma Division, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States.
Sara
S
Nowroozizadeh
Glaucoma Division, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States.
Nila
N
Cirineo
Glaucoma Division, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States.
Navid
N
Amini
Glaucoma Division, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States.
Shane
S
Knipping
Department of Computer Sciences, University of California San Diego, San Diego, California, United States.
Ted
T
Chang
Department of Biomathematics, David Geffen School of Medicine, University of California, Los Angeles, California, United States.
Tom
T
Chou
Glaucoma Division, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States.
Joseph
J
Caprioli
Glaucoma Division, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States.
Kouros
K
Nouri-Mahdavi
D000465:Algorithms; D003430:Cross-Sectional Studies; D005260:Female; D005901:Glaucoma / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence / Q000379:methods*
glaucoma imaging; ocular magnification; spectral-domain OCT