Photosensitization-induced retinopathy in the newborn beagle

Photosensitization is a mechanism by which oxygen and light may 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 exposure and a photosensitizer, rose bengal (RB), on the developing retina of the beagle puppy.

Seven purebred beagle puppies (2 or 7 days old) were given RB (7.5 mg/ml) intravenously (0.9 ml bolus followed by a 74 microliters/min constant infusion), and one eye was exposed to filtered light delivered by a modified slit lamp at 30 mW/cm2 for 5, 15, 25, 35, and 45 minutes. The fellow eye was not irradiated and served 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-only and no-treatment control eyes. Animals were followed clinically by indirect ophthalmoscopy and fluorescein angiography, and eyes were processed for light microscopy.

Clinical and/or histologic abnormalities were found in all seven eyes exposed to light in the presence of rose bengal, as follows: vitreous hemorrhage in four eyes, incomplete peripheral retinal vascularization in four eyes, fibrovascular/fibrocellular proliferation with traction on the retina in two eyes (including preretinal neovascularization in one eye), total or partial retinal detachment in two eyes, dilated peripheral vessels compatible with shunt vessels in one eye, retinal dysplasia with loss of normal architecture and formation of rosettes in five eyes. All 13 control eyes showed normal, complete retinal vascularization.

The failure to progress to the end-stage tractional retinal detachment seen in human infants is a shortcoming of existing animal models. Photosensitization injury to the developing retina in this animal model can produce a spectrum of retinal pathology that includes extraretinal vascularization and subsequent retinal detachment.