Biological features of the choriocapillaries after hypocrellin B photodynamic therapy

Fanguang LIU; Lina HAN; Ying GU; Li ZHANG; Hongxia CHEN

ABSTRACT

BACKGROUND:

The authors' experiments of the earlier stage proved that the hypocrellin B photodynamic therapy(HB-PDT) can cause selective injuries to choriocapillaries. It is not known whether changing the therapeutic parameters would gain a different result regarding the choriocapillaries after the hypocrellin B photodynamic treatment for a month.

OBJECTIVE:

To observe the features of Chinchilla rabbit choriocapillaries after HB-PDT treatment and to probe into the research prospect of using HB-PDT to treat choroidal neovascularization (CNV) and of using green light as the light source for PDT.

DESIGN:

A single sample study.

SETTING:

Laser Department of the Chinese PLA General Hospital.MATERIALS The trial was conducted at the Laser Department and the Department of Pathology of the Chinese PLA General Hospital as well as the Department of Photoelectric Engineering of Beijing University of Science and Engineering. The materials included photosensitizing agent hypocrellin B (HB), a green laser transmitter, fundus fluorescence camera and transmission electronic microscope.

METHODS:

The 532 nm green laser transmitter and slit-lamp microscope were connected by light fiber. Chinchilla rabbits of 2.5 to 3.5 kg was narcotized generally and HB(1. 0 mg/kg) was injected into the marginal ear vein. HB was excited with the green laser of 532 nm. The power density of the light spot on fundus was 300 mW/cm2, and the energy density 30 J/cm2. Laser was applied immediately after HB injection and the diameter of the light spot was 2 000 μm. Direct observation of retina, fluorescein fundus angiography and observation with light microscope and electronic microscope were conducted on the 1st, 7th and 28th days respectively after PDT to find the biological features of retina and the choroid.MAIN OUTCOME

MEASURES:

Non-selective injury of retina through direct observation of the fundus; obliteration of the choriocapillaries detected through fluorescein fundus angiography; the position and extent of non-selective injury in retina and the structural changes of the choriocapillaries observed through the light microscope; the ultrastructural changes of the fundus observed through the electronic microscope.

RESULTS:

One day after PDT, photodynamic thrombosis was formed in choriocapillaries being illuminated and the external layer of retina was apparently injured. On the 7th day, injury of endothelial cells of the choriocapillaries was aggravated without obvious changes of the main vessels of choroid. On the 28th days, fibrous tissue appeared where the choriocapillaries had been and the glass membrane became thickened. Repair and proliferation of RPE cells appeared in the laser illuminated area.

CONCLUSION:

The biological effect in the target area and non-selective injury in the non-target area began to appear from the 1st to the 7th day after PDT and continued to aggravate. That would be repaired by fibrous tissues from the 28th day. It deserves further studies to treat age-related macular degeneration or other diseases in fundus characterized with choroidal neovascularization.