Abstract
Purpose: :
To identify the specific retinal layers and macular areas damaged in glaucoma using Optical Coherence Tomography (OCT).
Methods: :
The Zeiss Stratus OCT system was used to map the macula over a 6 mm diameter (fast macular thickness map pattern) in three groups of patients – Normal (N), perimetric glaucoma (PG), glaucoma suspect and pre–perimetric glaucoma (GSPPG). OCT data was exported for automatic segmentation using a custom software program that we developed. The thicknesses of the following macular sublayers were measured: nerve fiber layer (NFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), inner retinal layer (IRL= NFL+ GCL+ IPL) and the total retina. The ability to differentiate between N, PG and GSPPG eyes was assessed using the area under the receiver operator characteristic curve (AROC).
Results: :
Forty–seven persons in the N group, 20 persons in the PG group and 32 persons in the GSPPG group were included in this study. Comparison of mean sublayer thicknesses between the GSPPG group and the N group showed the NFL (25.35 um vs 30.18 um), GCL (33.96 um vs 37.59 um) and IPL (32.83 um vs 37.44 um) were significantly thinner in the GSPPG group (p<0.0001). Similar comparisons between the PG group and the N group showed the macular NFL (23.21 um), GCL (32.45 um) and IPL (31.72 um) were significantly thinner in the PG group (p<0.0001). Discriminant power was optimized by combining the inner retinal layers. The area under the receiver operating curve was higher for IRL compared to total retinal thickness for discriminating between PG and N (0.91 vs. 0.83, p=0.014) and between GSPPG and N (0.82 vs. 0.79, p=0.332). In the GSPPG group, evaluating both macular IRL and peripapillary NFL thickness increased sensitivity (sensitivity=0.47) for the detection of glaucoma damage when compared to macular IRL (sensitivity=0.27) or peripapillary NFL thickness (sensitivity=0.35) alone.
Conclusions: :
The macular NFL, GCL and IPL layers appear to be thinner and damaged in persons with PG and pre–perimetric glaucoma. Measuring the inner retinal layers provides better discrimination between glaucomatous and normal persons compared to measuring the total macular retinal thickness. Mapping specific retinal layers over a wider area of the macula with OCT may further improve our ability to identify glaucoma damage.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • macula/fovea • nerve fiber layer