This prospective study investigated the relationship between IOP and the frequency of spontaneous venous pulsation (SVP) in primary open-angle glaucoma (POAG). The authors found that SVP was less common in patients with POAG than in glaucoma suspects, and among patients with POAG, SVP was less common in those with low IOP at all disease stages. These results are consistent with vascular factors having a more significant role in patients with POAG with low IOP than in those with POAG with higher IOP.
The authors used a confocal scanning laser ophthalmoscope (Spectralis) movie tool to measure SVP in 229 patients with POAG and 205 glaucoma suspects.
SVP was significantly more common in glaucoma suspects than among POAG patients (86.3 percent vs. 53.3 percent, P < 0.0001). Among POAG patients, it was the least frequent among those in the lowest tertile of IOP (< 15 mmHg, 40.2 percent) compared with those with IOP in the middle tertile (between 15 and 21 mmHg; 57.3 percent, P = 0.03) and highest tertile (greater than 21 mmHg; 63.9 percent, P = 0.003). The difference between the two groups with higher IOP was not significant.
In addition to IOP (P = 0.007), visual field mean deviation and refractive error were associated with frequency of SVP (P < 0.0001 and P = 0.011, respectively).
When analyzed within the same disease stage, SVP was less frequent among those with the lowest compared with the highest IOP in early (P = 0.011) and advanced (P = 0.044) glaucoma and marginally less frequent in moderate glaucoma (P = 0.080).
The reason for decreased SVP in glaucomatous patients is controversial, but it is thought to be due to increased retrolaminar venous resistance. Because increased venous resistance could reduce ocular blood flow, the SVP may be another method for evaluating retinal circulation and blood flow to the optic nerve, and it has been reported that the absence of SVP is a risk factor for glaucoma progression.
The use of the movie tool within the Spectralis HRA provides a motion correction tool, which may provide better recognition of SVP than direct observation through ophthalmoscopy. The authors believe that this may have been a reason for their finding that the frequency of SVP in glaucoma suspects in their study was higher than reported in previous studies.
The minimum IOP necessary to induce venous pulsation is venous pulsation pressure, which may be increased by an increase in venous resistance, which ultimately would result in a decrease in SVP. The combination of increased central retinal vein resistance and low IOP would result in a decrease in SVP, as was found in this study.
The finding that the absence of SVP is more common in low-tension glaucoma suggests that SVP's absence may be a causal factor in glaucoma. This also has been previously suggested as playing a causal role in the pathogenesis of glaucomatous damage. The authors suggest that if the absence of SVP is due to an increase in venous resistance, this may explain the frequency of optic disc hemorrhage in low-tension glaucoma.
They conclude that vascular factors may play a greater role in the pathogenesis of glaucoma in patients with low IOP if increased retrolaminar central retinal vein resistance is responsible for an absence of SVP.