It has been widely proven in literature that most optical microscopy techniques can greatly benefit from the application of adaptive optics correction of phase aberrations through an adaptive optical element, such as a deformable mirror or a spatial light modulator. However, adaptive optics is not yet widely adopted in the life sciences community, mostly due to the lack of adaptive commercial microscopy systems, and the inherent technical difficulty in modifying an existing microscopy setup to integrate an adaptive element, both on the software and hardware sides. We present a plug-and-play adaptive optics module for generic optical microscopes, based on a prototype refractive 18 actuators adaptive optical element, which can be inserted in any microscope between the objective and the microscope body. Correction is performed in a sensorless fashion, optimizing image quality metrics of the image presented to the user on screen. The results presented show how an end-user oriented commercial confocal laser scanning microscope (Leica SP5) can be upgraded with adaptive optics with minor hardware modifications, and no changes to the microscope control software.