Rabbit model of ocular indirect photodynamic therapy using a retinoblastoma xenograft.

PURPOSE: The goal of this project was to demonstrate the feasibility of coupling the indirect ophthalmoscope laser delivery system with the 690 nm wavelength diode laser used to perform photodynamic therapy (PDT) in the treatment of retinoblastoma. METHODS: For phase 1, a total of six pigmented rabbits were treated with the indirect laser delivery system. The laser source was provided by the Lumenis Opal 690 nm laser unit, delivered through a 810 nm Indirect ophthalmoscope headpiece and a hand-held 28-diopter indirect lens (1.0 mm spot size). Four rabbits received intravenous verteporfin at doses of 0.43 or 0.86 mg/kg, and two rabbits did not receive verteporfin (controls). A second phase of the study involved eight rabbits using a retinoblastoma xenograft to determine the effect of indirect PDT on subretinal tumors. RESULTS: For phase 1, a total of 20 laser treatments were performed in the right eyes of six rabbits. Laser power levels ranged between 40 and 150 mW/cm2 and treatment duration ranged between 1 and 3 min. In the four rabbits that received verteporfin, focal retinal scars were noted at 40 mW/cm2 and higher power levels. In the two control rabbits that did not receive verteporfin, thermal burns were confirmed at 75 mW/cm2 and higher power levels. Histopathology showed focal retino-choroidal scars at the site of PDT treatment, without evidence of generalized ocular damage. Using the retinoblastoma xenograft, the indirect PDT system was shown to cause areas of tumor necrosis on histopathology. CONCLUSIONS: The results of this pre-clinical study suggest verteporfin may be activated in the rabbit retina with the indirect delivery system and the 690 nm laser unit (i.e., Indirect PDT). Using verteporfin, treatment effects were observed at 40-50 mW/cm2 in the rabbit retina, while photocoagulation was achieved at 75 mW/cm2 and higher power levels. Fundoscopic and histopathologic examination of treated areas showed circumscribed areas of retinal damage and a lack of generalized ocular toxicity, suggesting that this modality may represent a safe and localized method for treating intraocular retinoblastoma.

Vitreous Seeds in Retinoblastoma: Clinicopathologic Classification and Correlation.

PURPOSE: A recent classification scheme for retinoblastoma vitreous seeds has shown promise in predicting treatment response. For the first time, we correlate this clinical classification scheme with its histopathologic features. DESIGN: Retrospective review. PARTICIPANTS: Enucleated eyes received at the pathology department of the Retinoblastoma Center of Houston from 2010 to 2015. METHODS: Macroscopic photographs of the enucleated eyes of patients with retinoblastoma were analyzed to select those with vitreous seeds. Cases with adequate material for clinicopathologic correlation were selected for further analysis, and clinical photographs were reviewed. Routine histopathologic slides were reviewed and compared with the clinical and macroscopic photographs. Seeds were classified as type 1 ("dust"), type 2 ("sphere"), or type 3 ("cloud"). To confirm the presence of macrophages, CD68 immunohistochemical staining was used. Synaptophysin was used to stain retinoblastoma cells. MAIN OUTCOME MEASURES: To correlate clinical vitreous seed type with histopathologic features. RESULTS: A total of 14 eyes with adequate amounts of tumor seeds along with clinical and macroscopic photographic correlation were selected from a total of 138 eyes reviewed. Type 1 seeds consisted of individual viable tumor cells and scattered macrophages. Type 2 seeds consisted of 2 submorphologies: spheres with viable cells throughout and spheres with an outer rim of viable cells but necrotic cells centrally. Type 3 seeds were composed of more than 90% necrotic material admixed with few macrophages and viable cells at their outer rim. Untreated (8/14) and previously treated (6/14) eyes showed similar histopathologic features for each type of seeds. Treated eyes had more type 1 and 3 seeds. CONCLUSIONS: We provide the first histopathologic correlation of the clinical classification scheme for vitreous seeds in retinoblastoma. "Dust" is formed by scattered single cells alternating with macrophages. "Spheres" with translucent centers contain multiple layers of viable tumor cells that shed single cells and may be more clinically aggressive. "Cloud" seeds are mostly composed of necrotic material, explaining their lack of therapeutic response. Pretreated eyes showed tumor seeds morphologically similar to untreated eyes. Knowledge of the underlying histopathology of vitreous seed types is a fundamental component of classification and may aid in understanding clinical response to treatment.