Parapapillary deep-layer microvasculature dropout is only found near the retinal nerve fibre layer defect location in open-angle glaucoma

Enlargement of microvascular dropout toward the disc-fovea axis indicates new central visual field defect in glaucoma

We aimed to evaluate the relationship between the increase in choroidal microvascular dropout (MvD) toward the disc-fovea axis and the development of central visual field defect (CVFD) in patients with glaucoma. We retrospectively reviewed the longitudinal medical records of patients who underwent at least two optical coherence tomography angiographies (OCTA) with significant macular retinal ganglion cell (RGC) damage at baseline. Patients were divided into three groups: Group 1, no CVFD; Group 2, new CVFD during the follow-up period; and Group 3, CVFD at baseline. The angular extent of MvD and the change were investigated. We had 35 eyes in Group 1, 25 in Group 2, and 43 in Group 3 with OCTA over an average of 3.1 ± 1.3 years. At baseline, MvD was significantly more frequent and larger in Group 3 compared to Groups 1 and 2; there was no difference between Groups 1 and 2, aligning with the absence of baseline CVFD. The mean final MvD extent was significantly smaller in Group 1 (9.9°) than Groups 2 and 3 (43.6 and 44.8°, P < 0.001), also aligning with the presence of final CVFD. Quantitatively, Group 2 with developing CVFD exhibited significantly greater mean increase in MvD (17.8°) than Groups 1 and 3 (0.9 and 6.0°, P < 0.001). In contrast, the changes in OCT-based thicknesses did not differ among the three groups in the period. In conclusion, in patients with glaucoma who had significant RGC damage in the macular area, longitudinal increase in MvD coincided with development of new CVFD, both in terms of the presence and in terms of angular extent, in a three-year follow-up period.

The Role of Optical Coherence Tomography Angiography in Glaucoma

Glaucoma is the leading cause of irreversible vision loss and comprises a group of chronic optic neuropathies characterized by progressive retinal ganglion cell (RGC) loss. Various etiologies, including impaired blood supply to the optic nerve, have been implicated for glaucoma pathogenesis. Optical coherence tomography angiography (OCTA) is a non-invasive imaging modality for visualizing the ophthalmic microvasculature. Using blood flow as an intrinsic contrast agent, it distinguishes blood vessels from the surrounding tissue. Vessel density (VD) is mainly used as a metric for quantifying the ophthalmic microvasculature. The key anatomic regions for OCTA in glaucoma are the optic nerve head area including the peripapillary region, and the macular region. Specifically, VD of the superficial peripapillary and superficial macular microvasculature is reduced in glaucoma patients compared to unaffected subjects, and VD correlates with functional deficits measured by visual field (VF). This renders OCTA similar in diagnostic capabilities compared to structural retinal nerve fiber layer (RNFL) thickness measurements, especially in early glaucoma. Furthermore, in cases where RNFL thickness measurements are limited due to artifact or floor effect, OCTA technology can be used to evaluate and monitor glaucoma, such as in eyes with high myopia and eyes with advanced glaucoma. However, the clinical utility of OCTA in glaucoma management is limited due to the prevalence of imaging artifacts. Overall, OCTA can play a complementary role in structural OCT imaging and VF testing to aid in the diagnosis and monitoring of glaucoma.

Comparative features of superior versus inferior hemisphere microvasculature dropout in open-angle glaucoma

PURPOSE

This study aimed to investigate differences in microvasculature dropout (MvD) between the superior and inferior hemispheres in glaucoma patients.

STUDY DESIGN

Retrospective and cross-sectional.

METHODS

Fifty-eight eyes of 58 open-angle glaucoma patients (age 61.12 ± 10.19 years, mean deviation - 7.32 ± 6.36 dB) were included. MvD was detected with en face images from swept-source optical coherence tomography angiography. Blood flow at the optic nerve head was measured with laser speckle flowgraphy, represented as the mean blur rate in tissue (MBRT). Logistic and linear regression models adjusted for age, intraocular pressure, axial length, and circumpapillary retinal nerve fiber layer thickness were used to investigate the relationship between various factors and MvD angle in each hemisphere.

RESULTS

The presence of inferior MvD was related to peripapillary atrophy-β area (odds ratio = 14.10 [2.49-234.00], P = 0.019). Superior MvD angle was significantly related to MBRT in the superior quadrant (β = -0.31 [- 0.60 - -0.02], P = 0.037). Inferior MvD angle was significantly related to peripapillary atrophy-β area (β = 0.49 [0.21-0.77], P = 0.001).

CONCLUSIONS

Only superior MvD demonstrated a significant relationship with reduced ocular blood flow. In contrast, inferior MvD was associated with mechanical stress. These findings may suggest a potential difference in pathophysiology between superior and inferior MvD.

Clinical characteristics of open-angle glaucoma progression with peripapillary microvasculature dropout in different locations

OBJECTIVE

The study attempted to identify clinical characteristics associated with structural progression in open-angle glaucoma (OAG) in the presence of MvD in different locations.

METHODS

A total of 181 consecutive OAG eyes (follow-up 7.3 ± 4.0 years), which demonstrated peripapillary choroidal MvD (defined as a focal capillary loss with no visible microvascular network in choroidal layer) on optical coherence tomography (OCT) angiography (OCTA), were divided based on the location of MvD. Structural progression was determined using trend-based analysis of the Guided Progression Analysis software of Cirrus OCT.

RESULTS

MvD was identified in the temporal quadrant in 110 eyes (temporal MvD; 60.5 ± 12.6 years), and in the inferior quadrant in 71 eyes (inferior MvD; 60.3 ± 11.1 years). After adjusting for age, average intraocular pressure (IOP) and baseline retinal nerve fibre layer (RNFL) thickness and visual field mean deviation, inferior MvD eyes showed faster rates of thinning in the inferior RNFL (mean (95% CI); -0.833 (-1.298 to -0.367)) compared to temporal MvD eyes (-0.144 (-0.496 to 0.207)) when long-term IOP fluctuation was larger than the median value (1.7 mmHg; P = 0.022). Long-term IOP fluctuations were independently associated with inferior RNFL thinning in eyes with inferior MvD (P = 0.002) but not in eyes with temporal MvD.

CONCLUSIONS

In OAG eyes, the rates of RNFL and GCIPL thinning were comparable regardless of MvD locations. However, inferior MvD is associated with faster RNFL and GCIPL thinning in the same quadrant when long-term IOP fluctuation is present. Structural progression in the presence of temporal MvD was less associated with IOP fluctuation.

Comparative Topographical Analysis of Choroidal Microvascular Dropout Between Glaucoma and Nonarteritic Anterior Ischemic Optic Neuropathy

Purpose

To identify the presence of choroidal microvascular dropout (MvD) in nonarteritic anterior ischemic optic neuropathy (NAION) eyes and to characterize the topographical distribution for the mechanistic interpretation of MvD development.

Methods

We performed optical coherence tomography angiography on 47 open-angle glaucoma (OAG) and 19 NAION eyes with β-zone peripapillary atrophy (βPPA). We recorded the presence of MvD and compared between the peripapillary topographical measures of MvD, retinal nerve fiber layer (RNFL) defect, and βPPA in angular width and location.

Results

MvD was present in both diseases, marginally more frequently in NAION eyes (19/19, 100.0%) than in OAG eyes (38/47, 80.6%, P = 0.050), without a discernable difference in appearance. NAION eyes also showed wider MvD and RNFL defects compared to OAG eyes (both P < 0.001). In topographical measurements, the distribution of MvD showed a strong correspondence to superimposition areas of βPPA and RNFL defects, more distinctly than to RNFL defects (all P < 0.001). The outline of superimposition area also remarkably resembled the MvD area.

Conclusions

MvD was present in both the OAG and NAION groups. The βPPA-RNFL defect superimposition area topographically and morphologically matched MvD. Further investigations are needed to elucidate the role of RNFL defects in the pathogenesis of MvD and the clinical significance.