A method for inspecting defects inside a glass core rod for the production of an optical fibre, the method comprising: - generating a first scanning beam of parallel light rays sweeping an inspection plane in a first scan direction; - directing the first scanning beam onto a transparent glass core rod for the manufacturing of an optical fibre, the core rod having a longitudinal axis and being arranged in such a way that the inspection plane is transverse to the longitudinal axis of the core rod and comprises a rod's cross-section; - detecting the first scanning light beam at an opposite side of the glass core rod that is interposed to intercept the parallel rays of the scanning beam, thereby producing a first electric output signal, and - processing the first electric output signal to produce a first light intensity profile in the first scan direction, the light intensity profile comprising a shadow region delimited by first and second shadow edges (53,54;74,74'), the width between the first and second shadow edges being indicative of the outside diameter of the core rod across the inspection plane, characterised in that the method further comprises: - analysing the first light intensity profile to determine the presence or absence of a peak of positive intensity within the shadow region, the peak originating from deflected rays transmitted through the core rod and detected, and, if an intensity peak (51;71) is determined to be present, to determine the presence or absence of a region of depressed intensity within the intensity peak, and - if, as a result of analysing, an intensity peak within the shadow region is determined to be absent or, if an intensity peak is determined to be present, a region of depressed intensity is determined to be present within the intensity peak, identifying the presence of at least one structural defect within the rod's cross-section. - generating a first scanning beam of parallel light rays sweeping an inspection plane in a first scan direction; - directing the first scanning beam onto a transparent glass core rod for the manufacturing of an optical fibre, the core rod having a longitudinal axis and being arranged in such a way that the inspection plane is transverse to the longitudinal axis of the core rod and comprises a rod's cross-section; - detecting the first scanning light beam at an opposite side of the glass core rod that is interposed to intercept the parallel rays of the scanning beam, thereby producing a first electric output signal, and - processing the first electric output signal to produce a first light intensity profile in the first scan direction, the light intensity profile comprising a shadow region delimited by first and second shadow edges (53,54;74,74'), the width between the first and second shadow edges being indicative of the outside diameter of the core rod across the inspection plane, characterised in that the method further comprises: - analysing the first light intensity profile to determine the presence or absence of a peak of positive intensity within the shadow region, the peak originating from deflected rays transmitted through the core rod and detected, and, if an intensity peak (51;71) is determined to be present, to determine the presence or absence of a region of depressed intensity within the intensity peak, and - if, as a result of analysing, an intensity peak within the shadow region is determined to be absent or, if an intensity peak is determined to be present, a region of depressed intensity is determined to be present within the intensity peak, identifying the presence of at least one structural defect within the rod's cross-section. - analysing the first light intensity profile to determine the presence or absence of a peak of positive intensity within the shadow region, the peak originating from deflected rays transmitted through the core rod and detected, and, if an intensity peak (51;71) is determined to be present, to determine the presence or absence of a region of depressed intensity within the intensity peak, and - if, as a result of analysing, an intensity peak within the shadow region is determined to be absent or, if an intensity peak is determined to be present, a region of depressed intensity is determined to be present within the intensity peak, identifying the presence of at least one structural defect within the rod's cross-section.