DYSFUNCTION AND REPAIR OF THE BLOOD RETINA BARRIER FOLLOWING WHITE-LIGHT EXPOSURE - A FLUOROPHOTOMETRIC AND HISTOLOGIC-STUDY

The purpose of this study was to pinpoint the site of blood-retina barrier disruption after white light exposure and determine the course of barrier repair. The retinas of 25 anaesthetized pigmented rabbits were exposed for 1 hr to the light of a xenon arc lamp filtered to eliminate ultraviolet and infrared light. The light intensities selected were near the threshold intensity causing visible retinal lesions in order to evaluate the function of the blood-retina barrier (BRB) in this range. Functional assessment of the BRB was made with vitreous fluorophotometry (VF), and electron microscopy (EM) after intra-arterial administration of horseradish peroxidase (HRP) as tracer. In 11 of the 14 rabbits exposed to threshold intensity (90-110 mW cm-2; retinal field of illumination, 0·64 cm2), a breakdown of the BRB was demonstrated by a 2-40-fold increase in the permeability of the BRB for fluorescein and by transcellular passage of HRP through the retina pigment epithelium (RPE). All 11 rabbits developed oedematous fundus lesions. Within a week, pigmentary alterations of the fundus were seen on ophthalmoscopy, while the BRB permeability for fluorescein and HRP had returned to normal. EM of the retina showed slight swelling of RPE during the period of increased permeability but no alterations of the neuroretina. After functional barrier repair, the RPE cells demonstrated irregularity of the melanin pigment alignment and some loss of the monocellular arrangement. In six rabbits exposed to subthreshold light intensity (65-89 mW cm-2) no fundus lesion developed and EM evaluation of the BRB was normal. All five superthreshold exposed rabbits (111-140 mW cm-2) developed ophthalmoscopically visible lesions, and VF and EM evidence of BRB permeability increase. In the range 65-140 mW cm-2, fluorescein leakage into the vitreous after a 1-hr exposure was found to increase exponentially with the light intensity starting at a value of 69 mW cm-2 (corresponding with 250 J cm-2; 95% confidence intervals, 200 and 280 J cm-2). The results show that low-intensity white light primarily affects the RPE cells in rabbit eyes inducing a temporary breakdown of the BRB. This functional disturbance can be quantified with fluorophotometry prior to the development of morphological or ophthalmoscopic changes. Functionally, the barrier recovers although morphologically, on ophthalmoscopy and EM, the retina remains altered. © 1992.