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Structural thinning may precede microvascular changes in early glaucoma
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Both ganglion cell complex density and macular vessel density significantly decrease in preperimetric and early primary open-angle glaucoma.
However, ganglion cell complex loss is greater than macular vessel density loss in early primary open-angle glaucoma (POAG), according to a study.
Although this suggest that microvascular changes may be secondary to structural thinning in early glaucoma, this inference “cannot be generalized to all glaucoma cases,” according to the authors.
In the study, 55 pre-perimetric subjects (68 eyes), 121 early glaucoma subjects (162 eyes) and 37 healthy subjects (57 eyes) were included. OCT angiography (OCTA) and spectral domain OCT (SD-OCT) imaging were performed to analyze microvasculature and structural changes within the macula. The AngioVue system, which has integrated OCT and OCTA facilities, was used.
As compared with healthy eyes, preperimetric and early POAG eyes had significantly lower ganglion cell complex (GCC) thickness and vessel density. GCC thickness loss was greater in the early POAG than in preperimetric eyes, while vessel density loss was similar.
In early POAG, GCC thickness percent loss was greater than vessel density loss.
As the authors noted, there has been increased interest in evaluating the macula to diagnose and manage glaucoma because macular changes occur early in the disease. In addition, the development of OCTA has been instrumental in providing evidence of the important role of microvascular changes in the pathophysiology of glaucoma.
The current study suggests that structural thinning might more often precede than follow microvascular changes in early glaucoma, but not in all cases, considering that one-third of the cases showed a greater percent loss in vessel density than in GCC thickness.
“The above inference cannot be generalized to all glaucoma cases,” the authors wrote, and added that “vascular change as the primary event in pathogenesis of glaucoma cannot be excluded.”
“Nevertheless, no matter whether neural tissue loss or vessel loss is the primary event, vascular abnormality and thickness change can be interdependent,” they wrote.
They also emphasized the fundamental role of OCT and OCTA in detecting early glaucoma. – by Michela Cimberle
Disclosure: Hou reported no relevant financial interests. Please see the published paper for the other authors’ financial disclosures.
Perspective
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Mark Eltis, OD, FAAO
Despite our armada of technological and pharmaceutical tools, many questions remain unanswered regarding the pathophysiology of glaucoma. The vascular theory vs. the neuronal destruction process is still a chicken-and-egg-type question. The real significance of this study for practice? It helps us determine what technology to invest in and gives some insight on how to utilize it most effectively.
Which systems are best for earliest disease detection, and which can accurately detect progression in more advanced cases? The need for ganglion cell analysis in concert with 10-2 visual fields in early detection has become clearer. Macular microvascular analysis with OCTA is of emerging importance, although it remains unclear what advantage it holds over GCC analysis.
This study suggests that structural damage precedes microvascular changes more often than not. This does not exclude the possibility that microvascular changes will be of greater significance in certain glaucoma populations, as one-third of the cases showed a greater percent loss in vessel density than in GCC thickness.
Ultimately, both technologies will likely play a role, but further studies are needed and may hopefully also shed light on the origins of the disease.
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