8 Several clinical studies confirmed that the decline in RGCs precedes functional changes detected on SAP in glaucomatous eyes, confirming that a combination of structural and functional tests might offer an optimal assessment of the neural damage and its progression. 3 – 7 However, it has been estimated that at least 25% to 35% of RGCs must be lost before producing significant abnormalities on the visual field. Standard automated perimetry (SAP) has been widely used to assess visual function in glaucomatous eyes for staging and monitoring the disease progression. Glaucoma is a heterogenous group of progressive neurodegenerative optic neuropathies characterized by the degeneration of retinal ganglion cells (RGC) and their axons in addition to significant remodeling of the lamina cribrosa of the optic nerve head. The use of a 10-2° visual field grid, adjusted for the anatomical RGCs displacement, describes more accurately the relationship between RGCs thickness and visual field sensitivity loss. The analysis of the structure-function relationship revealed a good agreement between the loss in retinal sensitivity and GCC thickness. Although the diagnostic accuracy increases with more severe glaucomatous damage and higher signal strength values, it is not affected by increasing axial length, resulting in a more accurate discrimination of glaucomatous damage in myopic eyes with respect to the traditional RNFL thickness.
The most accurate GCC parameters are represented by average and inferior GCC thicknesses, and they can be associated with progressive visual field loss. The average GCC thickness and its related parameters represent a reliable biomarker in detecting preperimetric glaucomatous damage. The macular ganglion cell complex (GCC), available in commercial Fourier-domain optical coherence tomography, allows the quantification of the innermost retinal layers that are potentially involved in the glaucomatous damage, including the retinal nerve fiber (RNFL), ganglion cell and inner plexiform layers. Glaucoma is a group of optic neuropathies characterized by a progressive degeneration of retina ganglion cells (RGCs) and their axons that precedes functional changes detected on the visual field.
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