What is the different between fractional laser and photodynamic therapy?

They are different: Photodynamic therapy(pdt) is a treatment which is used for treating some cancers and combines laser with an IV medication which makes cancer more sensitive to light treatments.

Chemical vs. Heat: Focal laser uses heat in ophthalmology to coagulate tissues proteins, stop leaky blood vessels, and destroy diseased tissues and tumors. Photodynamic therapy (pdt) uses a laser to chemically activate verteporphrin (visudyne) dye that is injected into a patient. The dye sticks to leaky blood vessels and the when activated by the laser, closes them off. Pdt laser does not heat up the tissues.

Injuries vs light: Fractional laser makes small injuries to a certain depth by destroying a target chromophore and then it heats the surrounding area. This causes new collagen formation. Pdt uses an agent to attach to a target like melanin and than it heats the target and surrounding tissue.