Abstract
Purpose :
To update a customizable model that maps visual field (VF) locations to sectors on the optic nerve head (ONH) allowing for new knowledge of the temporal raphe position and displacement of retinal ganglion cell (RGC) bodies from their photoreceptors in the macula.
Methods :
We reimplemented the model of Dennis et al. [1], separating it into two modules. The first generates a mapping of RGC bodies to one of 360 sectors on the ONH assuming the retinal surface is a sphere, the RGC density model given by Curcio et al [2], and the position and size of the ONH and raphe as parameters. The second maps any given visual field locations onto the surface of the sphere using displacement of RGCs in the macula according to the model of Drasdo et al. [3], and taking the nodal distance as a proportion of axial length as a parameter.
To explore the effect of ONH position on the mappings produced by the commonly used 6-sector mapping of Garway Heath et al [4], we generated 49 maps for the 24-2 VF pattern each with a different position of the ONH. For each map, we counted the number of VF locations that would not fall into the 6-sector map (allowing for a +- 5 degree wiggle in the sector boundaries). We assumed the raphe was horizontal throughout, as it is obvious that moving the raphe will alter the mappings for the far nasal VF points in the 24-2 pattern.
Results :
Figure 1 shows the results. When the ONH moves from (-15, 2) towards the fovea, there is little change in the 6-sector mapping, but moves away from the fovea, or towards the inferior retina causes large changes in the mapping.
Conclusions :
For eyes with an ONH that is nasally or inferiorly displaced form the population average of (-15,2) degrees, the commonly used 6-sector structure-function map is likely to misplace at least a quarter of the 24-2 pattern.
The code used to produce the custom maps in this study is available as a web app at http://go.unimelb.edu.au/4kg6.
[1] Denniss, Turpin, McKendrick. IOVS 55, 2014.
[2] Curcio, Allen. J Comp. Neuro. 300, 1990.
[3] Drasdo et al. Vision Res. 47, 2007.
[4] Garway-Heath et al. IOVS 43, 2002.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.