Photodynamic therapy (PDT) of the ciliary body with silicon naphthalocyanine (SINc) in rabbits.

BACKGROUND AND OBJECTIVE: To investigate silicone naphthalocyanine (SINc; 0.5 mg/kg) for photodynamic therapy (PDT) of the ciliary body in pigmented rabbits.

STUDY DESIGN/MATERIALS AND METHODS: SINc was dissolved in canola oil by heating, emulsified with Tween-80, and given by ear vein. Pharmacokinetics were studied in frozen sections by fluorescence microscopy using a CCD camera-based, low light detection system with digital image processing at 1 hr and 24 hr (12 rabbits, 24 eyes total). A Ti:Sapphire laser delivered light at 770 nm by contact fiberoptic (1,000 microns; 80 mW/cm2;20,40 and 80 J/cm2). Controls (5 rabbits), received laser light at 770 nm without SINc. For comparison, eyes received continuous wave Nd:YAG laser by fiberoptic contact (0.8-1.2 J).

RESULTS: Localization studies showed intravascular distribution shifting to a ciliary body distribution at 24 hr. PDT at 1 hr and 24 hr postinjection showed a more selective destruction of the ciliary body at 24 hr. Ciliary processes treated at 24 hr showed infarction and marked edema with sparing of iris. Tissue thermal damage was minimal in PDT controls. Eyes treated with the Nd:YAG laser exhibited full-thickness thermal necrosis of iris, ciliary processes, and a fibrinous iridocyclitis. In contrast, eyes treated by PDT were quiet with thrombosis of superficial blood vessels.

CONCLUSION: Tissue photon penetration is good at 770 nm and thermal effects from the exciting laser alone were minimal. The ciliary processes of pigmented rabbits exhibit a selective retention of SINc and on that basis can be selectively destroyed with a minimum on thermal damage to nontarget tissues.