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Potential Mechanisms of Intraocular Pressure Reduction by Micropulse Transscleral Cyclophotocoagulation in Rabbit
Hotaka Nemoto1, Megumi Honjo1, Michiaki Okamoto2
1Department of Ophthalmology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Purpose:
To evaluate the histological changes associated with, and the potential mechanisms of, intraocular pressure (IOP) reduction by micropulse cyclophotocoagulation (MP-CPC) in rabbit eyes.
Methods:
MP-CPC was performed on the right eyes of Dutch belted rabbits, whereas the left eyes served as controls. The laser power settings were 250, 500, 750, 1000, 1500, and 2000 mW, 10 seconds per sweep, 100 seconds in total. IOP, outflow facility, and uveoscleral outflow tract imaging, using a fluorescent tracer, were examined at one week after MP-CPC. Changes of morphology and protein expressions in the outflow tissues, conjunctiva, and sclera were also evaluated.
Results:
Significant reductions in IOP after MP-CPC were observed at 500 to 1000 mW (P = 0.036 and P = 0.014, respectively). The pre-MP-CPC IOP was 11.35 ± 0.41 mm Hg. At one week after surgery, the respective IOP values in the eyes treated at 500 mW and 1000 mW were 9.45 ± 0.49 mm Hg and 7.4 ± 0.27 mm Hg, respectively. Severe ciliary body damage was observed at 1500 to 2000 mW. MMP1-3 and fibronectin expression levels in the outflow tract and ciliary body were upregulated after MP-CPC. The α-smooth muscle actin (α-SMA) was upregulated at higher power levels. MP-CPC significantly increased uveoscleral outflow, whereas the outflow facility did not change. The α-SMA, collagen, and fibronectin were significantly upregulated in the subconjunctiva and sclera.
Conclusions:
Reactive fibrotic responses were observed in the outflow tract, conjunctiva, and sclera after MP-CPC. A potential mechanism of IOP reduction by MP-CPC in pigmented rabbit eyes may involve increased uveoscleral outflow related to MMP upregulation.
Insights
Micropulse cyclophotocoagulation (MP-CPC) effectively reduces intraocular pressure (IOP) in rabbit eyes by increasing uveoscleral outflow. Histological analysis revealed fibrotic responses and matrix metalloproteinase (MMP) upregulation as key mechanisms.
Area of Science:
- Ophthalmology
- Glaucoma Research
- Ocular Surgery
Background:
- Intraocular pressure (IOP) elevation is a primary risk factor for glaucoma.
- Micropulse cyclophotocoagulation (MP-CPC) is a surgical technique used to lower IOP.
- Understanding the histological changes and mechanisms of IOP reduction by MP-CPC is crucial for optimizing treatment.
Purpose of the Study:
- To investigate the histological alterations resulting from MP-CPC.
- To elucidate the potential mechanisms behind IOP reduction achieved by MP-CPC.
- To evaluate the effects of varying laser power settings on ocular tissues and IOP in a rabbit model.
Main Methods:
- MP-CPC was applied to rabbit eyes at different power settings (250-2000 mW).
- Intraocular pressure, outflow facility, and uveoscleral outflow were assessed one week post-procedure.
- Histological examination and protein expression analysis (MMP1-3, fibronectin, α-SMA) were performed on ocular tissues.
Main Results:
- MP-CPC significantly reduced IOP at 500 and 1000 mW, with notable decreases from baseline.
- Increased uveoscleral outflow was observed, while conventional outflow facility remained unchanged.
- Upregulation of MMPs, fibronectin, and α-smooth muscle actin (α-SMA) was detected in the outflow tract, ciliary body, conjunctiva, and sclera.
- Higher laser power settings (1500-2000 mW) resulted in severe ciliary body damage.
Conclusions:
- MP-CPC effectively lowers IOP in rabbit eyes, primarily by enhancing uveoscleral outflow.
- The IOP-lowering effect is associated with reactive fibrotic responses and upregulation of MMPs in ocular tissues.
- Optimal IOP reduction with MP-CPC is achieved at moderate power settings, avoiding severe ciliary body damage.
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