Probable Central Nervous System Mediated Enhancement of Perimacular Visual Function

Abstract

Purpose : The binocular visual field closely approximates to the higher light sensitivity level for each concordant locus of the individual right and left eye fields^1,2. This was reaffirmed³ during recent studies that confirmed CNS control of glaucomatous neurodegeneration when analyzing Humphrey (HVF) 30-2^3,4 and FDT⁵ visual fields. It was also revealed that binocular fields tend to generate pericentral threshold values greater than either eye alone. The present analysis was performed to determine whether this phenomenon represents a unique compensatory mechanism in diseased eyes or if it generalized to healthy eyes as well.

Methods : This case-control study compares bilateral and binocular perimacular function in patients with severe glaucomatous field loss (N=15) and control subjects with normal visual fields (N=5). HVF 30-2 was performed on right and left eyes monocularly and immediately thereafter binocularly¹. Visual fields were divided into six concentric zones with zone 1 representing the central four points, zone 2 the next co-isopteric ring of 8 loci, and so on. Mean threshold values were calculated for the left, right, composite and binocular visual fields. Paired t-tests were then performed for intra-subject zonal comparisons.

Results : Mean unilateral thresholds within zone 1 of the glaucomatous fields were 17.0 dB OD & 19.4 OS (18.2 dB average), 4.9 dB lower than the mean zone 1 binocular threshold (23.1 dB; p=0.0181). Control eyes demonstrated similar binocular enhancement, with mean zone 1 thresholds 32.7 dB OD & 32.6 OS (32.7 average), 2.3 dB lower than the mean binocular threshold (35 dB; p=0.0036). This tendency dissipated with the eccentricity from fixation, with co-isopteric mean values of the two eyes increasingly approximating the binocular mean.

Conclusions : Refined data analysis of binocular visual fields confirms enhancement of pericentral light sensitivity when both eyes are open. This phenomenon arose with the paired-eye/brain complex of all subjects, indicating an apparent role of the CNS in maximizing binocular central vision even when general function is diminished. This phenomenon may be another manifestation of the functionally interlocking spatial arrangement of the ocular dominance columns in the striate cortex^5,6.
1. Crabb et al. BJO 1998 2. Nelson-Quigg et al. IOVS 2000 3. Sponsel et al. TVST 2014 4. Sponsel et al. TVST 2015 5. Reilly et al. TVST 2015 6. Adams et al. J Neurosci 2007

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.