Aim-To identify if laser photocoagulation induces morphological changes spe
cifically related to the choroidal capillary endothelial processes that pro
trude into Bruch's membrane.
Methods-Two human eyes and one adult macaque monkey eye received retinal la
ser photocoagulation that was just suprathreshold, before enucleation or ex
enteration. They were examined by electron microscopy to determine the leng
th of the endothelial processes emanating from the choroidal capillaries in
the region around the laser burn. One human and two monkey untreated eyes
were used for comparison.
Results-In human eyes, there was no increase in the number of processes 15
hours after laser treatment but at 5 days the processes were more numerous
and longer within 400-500 mum of the burn than in the untreated half of the
same eye. The processes were longer 9 days after photocoagulation in the m
onkey, when compared with untreated monkeys, and some breached the elastic
lamina, a phenomenon not seen in the untreated eyes. Qualitative difference
s were also noted in the endothelial cell processes following photocoagulat
ion. Neovascularisation was not observed.
Conclusions-Protrusion of choroidal endothelial cell processes into Bruch's
membrane is a normal anatomical feature but the number, length, and morpho
logy of the processes change following mild photocoagulation. It is plausib
le that these processes may play a part in the clearance of debris from Bru
ch's membrane, and represent an early stage of angiogenesis. If the latter
is true prophylactic laser photocoagulation at just suprathreshold levels m
ay carry a risk of inducing choroidal neovascularisation.