Visual field evaluation and OCT examination

Visual field was measured by static automated perimetry using the Swedish Interactive Threshold Algorithm (Standard 24–2) of a Humphrey Field Analyzer (Carl Zeiss Meditec Inc., Dublin, California). Visual field measurements with fixation losses of more than 20%, or with over 33% false positives or false negatives were excluded from the analysis. Optical coherence tomography (OCT; Humphrey systems Inc., Dublin, CA) is a noninvasive, noncontact method that allows cross-sectional, in vivo imaging of intraretinal layers.[3] Anatomic layers within the retina can be imaged and quantitative assessment of RNFL thickness and macular thickness can be performed based on the different reflectivity properties of different layers. Spectral-domain (SD-) OCT, with its improved resolution, scan speed, and reproducibility compared with its predecessor, time-domain OCT, potentially leads to earlier and more accurate detection of glaucoma progression. Spectral-domain OCT has been used to evaluate the patterns of progressive RNFL defect and to estimate the number of retinal ganglion cells. Images with signal strength less than 6 were considered of poor quality and excluded from the data analysis. The circum-papillary RNFL thickness (cpRNFLT), the RNFLT in 4 quadrants, and 12-o’clock positions were used in the evaluation. RNFL defects were assessed clockwise in the right eyes and counter clockwise in the left eyes. In the 12 sector analysis at ONH, 7, 8, 10, 11, and 12 o’clock sectors in right eye is in correspondence to 5, 4, 2, 1, and 0 o’clock sectors in left eye, respectively. The OCT software automatically classified all RFNLT as within normal limits or abnormal (out of 95 percentile from age-matched healthy eye).