A Test of a Descriptive Model of the Boundaries of the Maculo-Papillary Region

Abstract

 

Purpose:

 

To develop a descriptive model of the borders of the maculo-papillary region (MPR) based upon tracings of retinal nerve fiber (RNF) bundles and to test this model with high density perimetry and frequency-domain (fd) OCT scans of eyes with glaucomatous damage of the macula.

 

Methods:

 

We defined the MPR as RNF bundles that do not arc around the fovea, but originate from the nasal side of the fovea and travel to the disc. Digital fundus photographs of 11 healthy eyes showing particularly well-defined RNF bundles were analyzed. The centers of the fovea and disc were determined and the RNF bundles traced from the twelve and six o’clock (OD) foveal locations to the disc by 2 observers. To test the model, one eye of each of 8 patients showing glaucomatous arcuate damage within the central 10° (10-2, HFA, Zeiss) was tested with a customized visual field (Haag-Streit, Inc) with double the density of 10-2 test points (diagonal spacing of 1.4°). Macular and optic disc fdOCT (Topcon, Inc) scans (3D cube, 128 B-scans) were obtained and the thickness of the RNF and retinal ganglion cell (RGC) plus inner plexiform layers determined [1,2]. Probability plots for the fdOCT thicknesses were created.[2]

 

Results:

 

The model: The 11 individual MPR borders showed good agreement when the fovea and disc centers were aligned by rotation and scaling [3]. Similar results were obtained by tracing fiber bundles seen in Fig. 2A of [3]. The test: The thinning on the fdOCT probability plots (fig: black, p<1%, region) was near the edge (5 eyes) or outside (3 eyes) the MPR (diagonal lines). After accounting for the displacement of RGC bodies near the fovea [2], the abnormal SAP data were seldom inside the MPR. Of 376 points with a loss in sensitivity greater than 5dB (e.g. gray region in fig), only 14 (3.7%) fell inside the MPR borders. Furthermore, only 8.3% of the points clearly within the MPR were <-5dB.

 

Conclusions:

 

The proposed MPR is relatively free of arcuate damage of the macula seen on fdOCT probability maps or high-density SAP tests of patients with glaucoma. When SAP test points are adjusted for RGC displacement [2], the model supplies an anatomical basis for the shape of the preserved "central isle" seen in advanced glaucoma.[4]  

 

Keywords: visual fields • imaging/image analysis: clinical • ganglion cells