Retinotopic organization of primary visual cortex in glaucoma: a method for comparing cortical function with damage to the optic disk.

PURPOSE

To demonstrate that the relationship between the functional organization of primary visual cortex (V1) and damage to the optic disc in humans with primary open-angle glaucoma (POAG) can be measured using a novel method for projecting scotomas onto the flattened cortical representation.

METHODS

Six subjects participated in this functional magnetic resonance imaging (fMRI) experiment. Structural damage to the optic disc and the retinal nerve fiber layer (RNFL) was measured by three techniques: scanning laser polarimetry (GDx ECC; Carl Zeiss Meditec, Dublin, CA), confocal scanning laser ophthalmoscopy (HRT II; Heidelberg Engineering, Heidelberg, Germany), and optical coherence tomography (StratusOCT; Carl Zeiss Meditec, Inc.). Cortical activity for viewing through the glaucomatous versus fellow eye was compared by alternately presenting each eye with a contrast-reversing checkerboard pattern. The resultant fMRI response was compared to interocular differences in RNFL or mean height contour for analogous regions of the visual field.

RESULTS

fMRI responses to visual stimulation were related to differences in RNFL thickness or mean height contour between eyes. The correlation between fMRI responses and measurements of optic disc damage for OCT (RNFL), HRT (mean height contour), and GDx (RNFL) were r = 0.90 (P = 0.02), r = 0.84 (P = 0.04), and r = 0.79 (P = 0.063), respectively. The probability of observing all three correlations by chance was low (P = 0.0003).

CONCLUSIONS

Cortical activity in human V1 was altered in these six POAG subjects in a manner consistent with damage to the optic disc. fMRI is a possible means for quantifying cortical neurodegeneration in POAG.