Threshold parameters for choroidal vessel closure with the photosensitizer, lambda 27

To determine the threshold photodynamic therapy parameters, required for choroidal vessel closure, with the photosensitizer, Lambda 27, in Dutch belted rabbits, using fluorescein angiography and histopathology.

A pre-clinical experiment.

Department of Ophthalmology at the Tulane University Health Sciences Center, between June 2001 - July 2002.

Dutch belted rabbits were divided into two groups. The first group was injected intravenously with an aqueous solution of Lambda 27 at 1mg/kg. Saline was injected intravenously into the second group (controls). Approximately 5 minutes after injection of Lambda 27, a diode laser, mounted on Zeiss 30 SL-M slit lamp, emitting light at a wavelength of 719 nm was used to apply photodynamic therapy to the fundus. Lesions were placed on the choroid of the rabbits at a fixed spot size of 1.5 mm, using powers ranging from 50 to 120 mW, for a duration of 5 to 80 seconds. Choroidal vessel closure was documented by fluorescein angiography, the following day, and by light microscopy, after the animals were sacrificed.

Choroidal vessel closure was documented using fluorescein angiography for all of the lesions placed at fluence of 22.7 J/cm2 and above. Histopathology also confirmed this finding. No choroidal vessel closure was seen in the rabbits treated with fluences less than 22.7 J/cm2 or in the control group.

This experiment establishes threshold parameters for choroidal vessel closure using the photosensitizer, Lambda 27.