The photoactivated agent produces {HEAD ~ activated oxygen species}, such as hydroxyl radicals and other radicals, that damage the new vessels, and may occlude {TAIL ~ the vessels} 
The photoactivated agent produces { HEAD ~ activated oxygen species } , such as hydroxyl radicals and other radicals , that damage the new vessels , and may occlude { TAIL ~ the vessels }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL