Research on optical fibers is of high interest because of the wide range of applications i.e. the automotive and aviation industry, medicine and laser technology. In comparison to glass fibers, polymer optical fibers (POFs) have a high mechanical durability but low optical radiation resistivity and high attenuation are limiting factors for possible areas of application. For this reason, this study is focused on the long-term behaviour of the laser-induced degradation applying a S-on-1 test series using a Nd:YAG nanosecond pulsed laser, with a wavelength of 532nm and a repetition frequency of 10Hz. In this investigation POFs were studied regarding different pulse energies and varying fiber parameters. For each test series, the degradation was determined by monitoring the fiber transmission. A CCD camera served as an in-situ detection method capturing scatter centers caused by the laser radiation. The scatter signal of the damages was monitored providing insight into the damage growth during irradiation. It is observed that a relative loss in transmission is caused by an increase in the scattering signal. After the test is completed, the ex-situ investigation of the laser-induced defects is performed by using differential interference contrast microscopy. Using this technique, the average damage density is determined in each fiber as well as the axial and radial position of the damages. It is observed that the damage density decreases with increasing radial position whereas the axial damage distribution is more or less homogenous. Additionally, the damage morphologies were studied using scanning laser optical tomography, scanning electron microscope and energy-dispersive X-ray spectroscopy, showing that the laser radiation can induce cavities inside the POF leading to a transmission loss. In addition, the formation and expansion of the cavities might be the reason of an increasing scatter signal during irradiation.