Retinal and choroidal vascular changes
Overall, after surgery, the values of RPC increased, although significant only in one parameter (peripapillary small vessel).
in macular area, vessel density at the level of superficial retina and choriocapillaris level, was observed to have a decrescendo trend which was significant in fovea and superior hemifield. In superficial layer, the vessel density of one more parameter, whole image, also showed a significant reduction.
Of note, the deep vessel density did not show a significant change in none of its parameters.
Abdolalizadeh et al proved that patients with Graves’ disease without TED had higher vessel density in whole image of optic disc and peripapillary area compared to healthy group but this vessel density decreases in patients with various grades of TED and DON. This decrease in optic disc vessel density in whole image and inside disc can deteriorate BCVA, visual field, and color vision tests. [14] so it is suggested to evaluate the result of this outcome in optic nerve function test.in univariate analysis non of single variants including: age, sex, IOP and smoking did not affect any of trends in vascular measuring elements.
A study evaluated the effect of smoking on both superficial and deep macular vessel densities and they found that superficial macular vessel density in superior parafoveal area is decreased in active smokers but had no difference compared to non-smokers. [15]
In Tehrani et.al study there was a significant decrease in both macula and pripapillary area in superficial and deep vascular layers between active TED and healthy controls so maybe it can be concluded that the activity of thyroid eye disease is one of the factors that impacts on the angiogenesis of retinal vasculature. [6]
In Lanchu Yu et.al study inactive TAO patients had a higher vascular density in whole image and pp region in comparison with active TAO and healthy controls also FAZ was significantly larger and central choroidal thickness was significantly higher in active TAO patients.[17].
Another study proved that patients with Graves’ ophthalmopathy had lower retinal capillary density in both superficial and deep layers compared to the control group. [9]
One study has shown that patients with inactive TED had increased superficial retinal vessels rather than active TED and healthy group. [16]
our study showed a decrease in blood vessel density in the superficial macula (whole image, superior Hemi, fovea, superior Hemi of parafovea) and choriocapillaris (superior Hemi, and fovea) layers.
Many studies have evaluated macular vessel density in patients with TED and have described that patients with active TED had lower macular vascular density in comparison with the healthy group. [5, 6] Also patients with inactive TED had significantly lower macular superficial vessel density in the whole en face and parafovea area compared to the healthy group. [7] Another study showed that macular vascular density (except fovea) in TED patients without DON is lower than in the control group but had no difference with DON patients. [8] In the study by Wu et al, it was shown that patients with DON and Non-DON thyroid ophthalmopathy had lower macular vessel density (in both superficial and deep layers) compared with the control group. [10]
In contrast to these studies, a few studies reported a significant increase in parafoveal vessel density, in temporal and nasal areas, in patients with inactive Graves’ ophthalmopathy compared to the healthy group. [17]
In current study, we found although small vessel density in peripapillary increased postoperatively, macular vessel density in the superficial layer (whole Image, Superior-Hemifield, Fovea, -Superior-Hemifield of ParaFovea) and choriocapillaris area (the Superior-Hemifield, and Fovea) decreased significantly postoperatively.
The study of Zhang et al. showed there was lower RPC density in the whole image, inside disc, and peripapillary in the group with no DON compared to the healthy group.[10]
Lewis et al. study showed that in patients with GO blood vessel density increases as a result of high orbital pressure which causes prelaminar venous enlargement. They evaluated the density of peripapillary vessels in patients with moderate to severe TED both before and 43 days after orbit decompression surgery by OCT-A. The vascular density in the area inside the optic disc decreases after surgery on the 18/24 eyes (with DON and without DON). Although in eyes with DON the decrease in vascular density in the peripapillary ring was seen in 4/6 of eyes, in eyes without DON this change was seen only in 7/18 of eyes. This study showed DON improvement is associated with a decrease in vascular density inside the optic disc area after surgery. In this study, the reason for the decrease in vascular density after decompression was a decrease in intraorbital pressure. [18]
Contrary to this study, our study showed an increase in small vessel density in the peripapillary area but changes inside the disc area were not significant postoperatively.
In the study of Mihailovic et al., peripapillary OCT-A was used to compare inactive TED and healthy groups; lower RPC was reported in patients with inactive TED. [7] Also in our study, the peripapillary RPC small vessel density increased postoperatively.
Interestingly, values for peripapillary RNFL thickness showed a reduction trend which was significant when measuring the total and inferior hemifield.
The mean RNFL thickness decreased after surgery in the peripapillary, and -Inferior-Hemifield region.
Studies evaluating RNFL thickness in patients with TED showed that patients with active TED had higher RNFL thickness rather than patients with inactive TED and healthy group. [5] A study explained that there was no difference in RNFL thickness between no DON and the healthy group. [8]
Contrary to these studies, other studies investigated that patients with TED had lower RNFL thickness rather than the control group. [10, 16] Another study showed that both patients with moderate to severe TED and DON group had lower RNFL thickness in inferior-Hemifield compared to healthy group. They proved that the cause of this is the decrease in retinal vessel density in TED patients. [14]
study by SayJn et al., had shown that patients with thyroid ophthalmopathy had lower RNFL thickness in the inferior quadrant, and in ONH analysis their cup to disc ratio and disc area were greater compared to the control group. But our study showed decreasing peripapillary RNFL thickness, and increasing cup/disc horizontal ratio following decompression surgery, but disc area and cup/disc area didn’t show any change. [19] Peripapillary RNFL thickness decreasing following decompression surgery has been shown in other studies. [11, 12]
In the study by Hsia et al, explained that after orbital decompression surgery, average RNFL thickness is reduced in patients with TED (both in DON, and Non-DON groups). In TED with DON, it is because of optic nerve destruction or disc edema reduction after surgery. But in the TED group that didn’t undergo decompression surgery this reduction in RNFL thickness had not seen. In Non-DON group average cup/disc ratio, vertical cup/disc ratio, and cup volume increased postoperatively. After decompression surgery in the Non-DON group, RNFL thickness in all quadrants (except in the temporal quadrant) decreased significantly. [13]
Our study showed decreasing peripapillary, and inferior hemifield RNFL thickness, and increasing cup/disc horizontal ratio following decompression surgery, but disc area and cup/disc area didn’t show any change.