Relevance of choroidal change in glaucoma has long been a focus of interest in glaucoma research. The interest has been boosted recently since the description of parapapillary choroidal microvascular dropout (MvD) using OCT Angiography (OCTA) in glaucomatous eyes. It is acknowledged that choroidal thickness varies according to IOP change. Particularly, several studies demonstrated choroidal thickening weeks or months after trabeculectomy. However, there has been paucity in the literature about longer term effect of IOP lowering on the choroidal thickness. Kojima et al. reported thickening of the macular and peripapillary choroidal thickness after one year after trabeculectomy. Interestingly, the thickening was mostly due to the increases in the interstitial areas, while the luminal area was comparable to the preoperative state.
An interesting issue regarding the role of choroid in glaucoma is that how the optic nerve head perfusion is related with choroid. While the choroid is responsible for supporting the outer retina, which is considered not to be closely associated with glaucoma, peripapillary choroid is closely related with ONH perfusion. At least, peripapillary choroid and the deep ONH are both supplied from the branches of short posterior ciliary artery. Further, Hayreh has claimed that prelaminar tissue is supplied by the centripetal arterioles entering from the peripapillary choroid based on angiographic studies. According to his concept, the ONH perfusion would be strongly dependent on the choroid. If the choroid is atrophic with obstruction or obliteration of the choroidal vessel, the prelaminar tissue perfusion would be significantly hampered. On the other hand, corrosion casting technique has shown that the prelaminar perfusion is mostly dependent on the branches from the short posterior ciliary artery which directly (i.e., not passing through the choroid) pierces through the sclera. Yet several small centripetal arterioles were found between the peripapillary choroid and the optic nerve head suggesting that prelaminar tissue perfusion is at least partly dependent on the peripapillary choroid.
Slowing of glaucoma progression after IOP lowering treatment may be, at least partly, attributed, to the improved perfusion to the optic nerve
The interstitial tissue contains pigment cells, smooth muscles, neurons, vascular walls, inflammatory cells, and connective tissue. It is unknown whether increases of interstitial tissue alone (i.e., no change in the ruminal area) can increase the blood flow. Therefore, further study is needed to elucidate whether increase of interstitial tissue area without increase of luminal area may increase perfusion. Meanwhile, it is worthy of note that increase of ONH microvasculature has been observed after trabeculectomy in other study. It remains to be determined whether the increase of ONH vasculature is related with increase of choroidal thickness or attributed to reduction of compression of ONH connective tissue, but the finding suggests that slowing of glaucoma progression after IOP lowering treatment may be, at least partly, attributed, to the improved perfusion to the optic nerve head.