Morphological changes to Schlemm's canal and the distal aqueous outflow pathway in monkey eyes with laser-induced ocular hypertension

Segmental Uveoscleral Outflow and its Relationship With Trabecular Outflow in Monkey Eyes

Purpose

Segmental trabecular outflow has been observed in various species, and we recently reported segmental uveoscleral outflow in mouse eyes. However, whether this pattern exists in other species remains unclear. This study aimed to investigate segmental uveoscleral outflow and its correlation with trabecular outflow in monkey eyes.

Methods

Five healthy eyes of aged cynomolgus macaques were examined. After anesthesia, a fixed volume of tracer was injected into the anterior chamber and allowed to diffuse for 45 minutes before fixation. The eyes were dissected into 12 radial segments, and images were captured using a confocal microscope. Segments were randomly selected for histological study. Tracer intensity and stromal thickness were measured.

Results

Four distinct tracer patterns were observed: (1) low flow in both pathways, (2) high flow (HF) in both, (3) HF in trabecular outflow, and (4) HF in uveoscleral outflow. As trabecular outflow contributed 75% of the total outflow, the "HF in uveoscleral outflow" pattern was the least frequent. Segmental flow patterns were observed in both outflow pathways, including components along the uveoscleral outflow pathway: supraciliary and suprachoroidal spaces, spaces between muscle bundles, and ciliary stroma. A positive correlation was found between tracer intensity along the uveoscleral outflow pathway and stromal thickness.

Conclusions

Uveoscleral outflow is segmental and uncorrelated with trabecular outflow in monkey eyes. It primarily occurs in the ciliary stroma, where it positively correlates with stromal thickness. Future studies in human eyes may inform the optimal placement of drainage devices and drug delivery systems targeting the uveoscleral outflow pathway.

Surgery Outcomes of Prolene Suture Gonioscopy-Assisted Transluminal Trabeculotomy (GATT): Up to 4 Years Follow-Up and Prognostic Factors

PRCIS

Long-term success was achievable after GATT. GATT performed at early stage of glaucoma had better surgery outcomes. Trabeculoplasty may compromise surgery success.

PURPOSE

To evaluate the long-term effectiveness of prolene suture gonioscopy-assisted transluminal trabeculotomy (GATT) and identify factors that may affect surgical outcomes.

PATIENTS AND METHODS

This is a retrospective cohort study of adult patients with prolene suture GATT performed by a single surgeon at 1 medical center.

RESULTS

Of the 145 eyes from 124 patients studied, intraocular pressure was reduced from 22.1±7.8 to 15.1±3.2 and 15.1±3.5 mm Hg, and the number of glaucoma medications was reduced from 3.2±1.1 to 1.3±1.4 and 1.4±1.5 at postoperative years 3 and 4, respectively. Ninety-three and 71 eyes completed a 3- and 4-year follow-up, with 44% of the eyes at year 4 remaining medication free. Compared with eyes with combined GATT/cataract extraction (CE), eyes with GATT alone had significantly more preoperative medications and a higher reoperation rate (31% vs. 16.5%). Eyes with prior trabeculoplasty had a higher reoperation rate (28.8%) than those without (16.1%). Kaplan-Meier survival analysis revealed that GATT/CE eyes without trabeculoplasty had a longer median time to failure (48 mo) than GATT/CE eyes with trabeculoplasty (18 mo), and GATT eyes with or without trabeculoplasty (9 and 12 mo, respectively).

CONCLUSION

Prolene suture GATT successfully reduced IOP. Eyes with more preoperative medications responded less well to GATT. Prior laser trabeculoplasty was associated with poorer outcomes. Further study is needed to verify these findings.

Segmental Unconventional Outflow in Mouse Eyes

Purpose

To investigate the flow pattern in unconventional outflow and its correlation with conventional outflow in mouse eyes.

Methods

Fluorescent microspheres were injected into the anterior chamber of one eye of anesthetized C57BL/6J mice (n = 4), followed by perfused fixation with 4% paraformaldehyde in situ after 45 minutes. Post-euthanasia, the injected eyes were enucleated, further immersion fixed, and dissected into 12 equal radial segments. Both sides of each segment were imaged using a confocal microscope after nuclear counterstaining. Both unconventional and conventional outflow patterns of each eye were analyzed by ImageJ and ZEN 2.3 imaging software.

Results

Segmental outflow patterns were observed in both the ciliary body (CB) and the supraciliary space and suprachoroidal space (SCS). In the CB, the tracer intensity was the lowest at 12 o'clock and highest at 9 o'clock, whereas in the SCS it was the lowest at 2 o'clock and the highest at 10 o'clock. Consequently, a segmental unconventional outflow was observed, with the lowest and highest flow regions in the superior and temporal quadrants, respectively. The overall segmental uveoscleral outflow has no correlation with trabecular outflow (P > 0.05). Four different outflow patterns were observed: (1) low-flow regions in both outflows, (2) primarily a high-flow region in conventional outflow, (3) primarily a high-flow region in unconventional outflow, and (4) high-flow regions in both outflows.

Conclusions

Uveoscleral outflow is segmental and unrelated to the trabecular segmental outflow. These findings will lead to future studies to identify the best location for the placement of drainage devices and drug delivery.

In vivo quantification of human aqueous veins by enhanced depth imaging optical coherence tomography and optical coherence tomography angiography images

AIM

To investigate the aqueous vein in vivo by using enhanced depth imaging optical coherence tomography (EDI-OCT) and optical coherence tomography angiography (OCTA).

METHODS

In this cross-sectional comparative study, 30 healthy participants were enrolled. Images of the aqueous and conjunctival veins were captured by EDI-OCT and OCTA before and after water loading. The area, height, width, location depth and blood flow of the aqueous vein and conjunctival vein were measured by Image J software.

RESULTS

In the static state, the area of the aqueous vein was 8166.7±3272.7 µm2, which was smaller than that of the conjunctival vein (13 690±7457 µm2, P<0.001). The mean blood flow density of the aqueous vein was 35.3%±12.6%, which was significantly less than that of the conjunctival vein (51.5%±10.6%, P<0.001). After water loading, the area of the aqueous vein decreased significantly from 8725.8±779.4 µm2 (baseline) to 7005.2±566.2 µm2 at 45min but rose to 7863.0±703.2 µm2 at 60min (P=0.032). The blood flow density of the aqueous vein decreased significantly from 41.2%±4.5% (baseline) to 35.4%±3.2% at 30min but returned to 45.6%±3.6% at 60min (P=0.021).

CONCLUSION

The structure and blood flow density of the aqueous vein can be effectively evaluated by OCT and OCTA. These may become biological indicators to evaluate aqueous vein changes and aqueous outflow resistance under different interventions in glaucoma patients.

Endothelial Glycocalyx Morphology in Different Flow Regions of the Aqueous Outflow Pathway of Normal and Laser-Induced Glaucoma Monkey Eyes

Glycocalyx morphology was examined in the trabecular outflow pathway of monkey eyes with and without experimental glaucoma. Laser burns were administered along ~270 degrees of the trabecular meshwork (TM) of one eye (n = 6) or both eyes (n = 2) of each monkey until intraocular pressure remained elevated. Portions of the TM were not laser-treated. Unlasered eyes (n = 6) served as controls. Enucleated eyes were perfused at 15 mmHg to measure the outflow facility, perfused with fluorescein to evaluate the outflow pattern, perfusion-fixed for glycocalyx labeling, and processed for electron microscopy. Coverage and thickness of the glycocalyx were measured in the TM, Schlemm’s canal (SC), collector channels (CCs), intrascleral veins (ISVs), and episcleral veins (ESVs) in non-lasered regions and high- and low-flow regions of controls. Compared to controls, laser-treated eyes had decreased outflow facility (p = 0.02). Glycocalyx thickness increased from the TM to ESVs in non-lasered regions and controls (p < 0.05). Glycocalyx coverage was generally greater distally in non-lasered regions (p < 0.05). In lasered regions, TM, SC, and CCs were partly to completely obliterated, and ISVs and ESVs displayed minimal glycocalyx. Whether the glycocalyx is decreased in the trabecular outflow pathway of human glaucomatous eyes warrants investigation.