A wind turbine comprising an elongated blade body, a system for detecting an ice layer on the blade body, the system comprising a light source for emitting a light beam; a light splitting optical element optically connected to the light source so as to receive the light beam emitted from the light source, the optical element adapted to split the light beam received from the light source into a reference light beam and a detecting light beam, a boundary area which is arranged at the blade body so as to be exposed to the outer surroundings of the blade body and which is optically connected to the light splitting optical element such as to receive the detecting light beam and to reflect an internal reflected part of the detecting light beam at the boundary area and to transmit a transmitting part of the detecting light beam to the outer surroundings of the blade body through the boundary area and to allow an external reflected part of the transmitting part of the detecting light beam, which has been reflected from outside of the blade body, to be re-transmitted through the boundary area, a light measuring device optically connected to the light splitting optical element so as toreceive the reference light beam, the internal reflected part of the detecting light beam and the external reflected part of the detecting light beam, wherein the light measuring device is configured to analyze the received light and to determine the presence and/or thickness of an ice layer on the blade body dependent on the analysis.