15 How Does Cyclodestruction Affect the Blood–Aqueous Barrier? In the past, cyclodestruction was performed by various methods, including surgical excision, diathermy, cryotherapy, and laser. Nowadays, laser cyclophotocoagulation (CPC) is the principal method for reducing aqueous inflow.1 However, all of these treatments cause a certain level of damage to the nonpigmented layer of the ciliary epithelium, which forms the blood–aqueous barrier (BAB), and thus might break down the immune privilege status within the eye. Transscleral diode cyclophotocoagulation (TCP) is a popular choice because of its relatively good tolerance and efficacy, which may be due to its theoretical advantages of effective penetration and selective absorption by the pigmented tissue of the ciliary body. A newer method to directly photocoagulate the ciliary processes within the eye using direct endoscopic visualization, known as endoscopic diode cyclophotocoagulation (ECP), is increasingly used to treat refractory glaucoma in eyes with relatively intact central visual acuity.2 Transscleral diode cyclophotocoagulation has been shown to induce significant damage (including coagulative necrosis) to the pars plicata and surrounding tissues, including the sclera, iris, and pars plana.3 However, during ECP treatment, typically only the raised processes are treated without affecting the “valleys” between processes, which could control the damage so that it is more specific and localized. Furthermore, laser energy is applied to each process just until shrinkage and whitening occur, which may avoid excessive energy (when the process explodes or “pops” with bubble formation), leading to excessive inflammation and further breakdown of the BAB.1 However, there have not been any studies to assess how these cyclophotocoagulative procedures affect the functional BAB, but indirect evidence enables us to speculate based on histological and clinical findings. Our group at University of California, San Francisco (UCSF) studied the acute and late effects of TCP and ECP on the histology and ciliary blood flow in rabbits.4
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