Yuya Hirata

The choroidal circulation assessed by laser-targeted angiography

The choroid plays an important role in supplying nutrients to and removing waste products from the outer region of the retina. Abnormal choroidal blood flow can disrupt normal retinal function and lead to alterations in visual function. Visualization of the choriocapillaris in vivo is a great challenge to understanding its normal physiology and involvement in the disease process. Laser-targeted angiography (LTA) is a relatively new method used to visualize and analyze the choroidal circulation. Carboxyfluorescein (CF), encapsulated in heat-sensitive liposomes, is released locally in the choroid through the application of a heat beam provided by an infrared laser. Video angiograms are generated with excitation illumination provided by an argon laser. Obtained images are highly selective to the choriocapillaris and are sharply contrasted against underlying and overlying structures. The images can be obtained repetitively, during which period the circulating liposome concentration is sufficient to generate adequate angiograms. These high-quality images have revealed three distinct phases (filling, plateau, and draining) of the choriocapillaris. In the plateau phase, a cluster of lobules fed by a common arteriole has been uniformly illuminated. This defined cluster area does not change in size while an infrared laser is continuously applied to the same spot, which demonstrates that each cluster is functionally independent and no physiological communication exists between them. Only in posterior regions do the angiograms demonstrate during the filling and draining phases that each lobule is filled from a central spot and drained along a peripheral ring, showing honeycomb flow patterns. The regional differences in choriocapillaris flow patterns revealed by LTA suggests that the choriocapillaris provides a more highly efficient system of outflow in posterior regions than in peripheral regions. LTA is useful in analyzing choroidal circulation in vivo and has the potential for clinical application in the future. Additionally, LTA has a unique capability to image choroidal neovascularization in animal models and it promises potential application in age-related macular degeneration (AMD).

Quantitative evaluation for blood-retinal barrier breakdown in experimental retinal vein occlusion produced by photodynamic thrombosis using a new photosensitizer

Purpose. To establish a rat model of retinal vein occlusion (RVO), we applied photodynamic thrombosis using a new photosensitizer. By measuring the breakdown of the blood-retinal barrier (BRB), we evaluated the model quantitatively. We also investigated how hypertension and retinal pigment epithelium (RPE) influence the breakdown of BRB after RVO. Methods. We modified a slit lamp biomicroscope for photodynamic thrombosis. The light source was changed from white light to argon laser, which made it possible to perform fluorescein angiography (FAG) simultaneously during photodynamic thrombosis. We irradiated with a continuous diode laser to occlude three retinal veins in a rat after PAD-S31 injection. The breakdown of BRB was quantitated by measuring extravasated Evans blue dye in albino and pigmented rats. We compared hypertensive rats (SHR) to nor-motensive rats (WKY) and sodium iodate-treated rats to normal rats. Results. High photosensitivity of PAD-S31 made it possible to occlude any retinal veins within 120 seconds at a low dose of 10 mg/kg without retinal thermal burn at the occlusion site. Simultaneous FAG enabled us to observe the formation of thrombus during diode laser irradiation. Our measured value of intraretinal Evans blue correlated with the range of serous retinal detachment. Both albino and pigmented rats demonstrated stable and constant values of Evans blue. SHR recovered from the breakdown of BRB after venous occlusion more slowly than WKY. Sodium iodate-treated rats had smaller breakdowns of BRB and recovered earlier than normal rats. Conclusions. In this study, we established the stable and constant rat model of RVO efficiently by using a new photosensitizer. Our simultaneous FAG method was considered to have an advantage of several potential clinical applications. Our rat model of RVO allows us to study factors associated with the recovery from damage by RVO.

Iridociliary melanocytoma with suspected pulmonary metastasis.

Melanocytoma is a benign tumor that is usually located over the optic nerve head, but may occur rarely in the iris, ciliary body, or choroid. 1 Because this deeply pigmented tumor may grow progressively, 2 invade the surrounding ocular tissues, 3 or cause secondary glaucoma, 4 it is sometimes difficult to clinically differentiate melanocytoma from malignant melanoma prior to histopathologic diagnosis. This report concerns a case of iridociliary melanocytoma with pulmonary mass lesion that initially simulated malignant melanoma with pulmonary metastasis.