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P. Margaron, R. Li, K. Nelchenbrecher, K. Gibbon, R. Kjellbotn, G. Lewis, C. Smits; Effects of laser spot size on the chorioretinal responses to PDT in the rabbit. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3186.
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Purpose: To investigate the effects of spot size and light dose on the responses of the chorioretina to photodynamic therapy (PDT) in the rabbit. Methods: Dutch Belted rabbits were administered an intravenous bolus injection of 0.2 mg/kg verteporfin (Visudyne®, Novartis AG). Fifteen minutes later, the retinas were exposed to 20, 25, or 50 J/cm2 of 689–nm laser light (600 mW/cm2) applied on a 3 mm diameter spot; or 6, 15 or 25 J/cm2 applied on a 5 mm diameter spot. The rabbits were monitored for 14 days, during which the effects of PDT on the posterior segment were assessed by indirect ophthalmoscopy on Days 1, 2, 3, 7 and 14 and fluorescence angiography on Days 3, 7 and 14 after PDT. At Day 14, the animals were sacrificed and chorioretinal tissues collected for histopathological evaluation. Results: The inflammatory and vascular responses to PDT in the chorioretina were light–dose dependent regardless of the spot size. Responses ranged from undetectable at a dose of 6 J/cm2 applied on a 5 mm spot to vaso–occlusion, massive inflammation and retinal damage at 25 J/cm2 on a 5 mm spot. The milder the inflammation and vascular changes at Day 1, the faster they resolved over time. In most eyes, the retinal spots exposed to inflammatory doses of PDT displayed alteration of fundus pigmentation by Day 7. The intensity of the responses to PDT was also related to the spot size. A dose of 25 J/cm2 applied on a 3 mm spot caused a minor inflammatory response that resolved over 3 days; it affected neither choriocapillaris perfusion nor the neurosensory retina at Day 3, in contrast to the same dose applied on a 5–mm spot. Conclusions: The study demonstrated that the vascular and inflammatory responses to PDT are light–dose and spot–size dependent in the rabbit chorioretina.
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