PHOTOSENSITIZATION-INDUCED RETINOPATHY IN THE NEWBORN BEAGLE

Purpose. Photosensitization is a mechanism by which oxygen and light m ay interact to generate free radicals capable of tissue injury. It has been proposed as a possible etiologic mechanism in the development of retinopathy of prematurity. The authors report the effects of light e xposure and a photosensitizer, rose bengal (RB), on the developing ret ina of the beagle puppy. Methods. Seven purebred beagle puppies (2 or 7 days old) were given RB (7.5 mg/ml) intravenously (0.9 ml bolus foll owed by a 74 mu l/min constant infusion), and one eye was exposed to f iltered light delivered by a modified slit lamp at 30 mW/cm(2) for 5, 15, 25, 35, and 45 minutes. The fellow eye was not irradiated and serv ed as an RB-only control. Three beagles were exposed to light (one eye only) for 15 to 120 minutes in the absence of RB to provide light-onl y and no-treatment control eyes. Animals were followed clinically by i ndirect ophthalmoscopy and fluorescein angiography, and eyes were proc essed for light microscopy. Results. Clinical and/or histologic abnorm alities were found in all seven eyes exposed to light in the presence of rose bengal, as follows: vitreous hemorrhage in four eyes, incomple te peripheral retinal vascularization in four eyes, fibrovascular/fibr ocellular proliferation with traction on the retina in two eyes (inclu ding preretinal neovascularization in one eye), total or partial retin al detachment in two eyes, dilated peripheral vessels compatible with shunt vessels in one eye, retinal dysplasia with loss of normal archit ecture and formation of rosettes in five eyes. All 13 control eyes sho wed normal, complete retinal vascularization. Conclusions. The failure to progress to the end-stage tractional retinal detachment seen in hu man infants is a shortcoming of existing animal models. Photosensitiza tion injury to the developing retina in this animal model can produce a spectrum of retinal pathology that includes extraretinal vasculariza tion and subsequent retinal detachment.