An applanation tonometer head, comprising a transparent integral body with rotational symmetry having a longitudinal axial direction, defining: at a first end along said longitudinal axial direction, an end portion defining a flat circular or elliptical corneal applanation surface, having a respective applanation radius or semi-axis, arranged on a first base plane of the end portion orthogonal to a longitudinal axis of the tonometer head, and having a second base parallel to said flat corneal applanation surface; a second portion, distinct from said end portion and integral with it, having a respective major base having a second radius or second semi-axis and arranged on a second plane orthogonal to said longitudinal axial direction, and a respective minor base along a third cross section arranged on a third plane orthogonal to said longitudinal axial direction and having a third radius or third semi-axis smaller than said second radius or second semi-axis, respectively, said second portion having a respective external lateral surface comprised between said major base and said minor base, at least a zone of said external lateral surface being inclined with respect to said corneal applanation surface by a respective internal angle comprised between 0° and 80° and being configured to define a rectilinear light path so that a light shaft incident on the external lateral surface from outside of the applanation head enters said second portion and propagates in said end portion up to said flat corneal applanation surface without to be reflected and without encountering material discontinuity surfaces; two semi-cylindrical or semi-elliptical prisms (4a, 4b), each having: - a respective semicircular or semi-elliptical lower base integral with said second portion and arranged along a fourth plane orthogonal to said longitudinal axial direction; - a nominal height at a center of the respective semi-circular or semi-elliptical lower base; - a semi-elliptical upper base surface opposite to said respective lower base and inclined with respect to the lower base by a respective internal angle comprised between 10° and 60°; said two semi-cylindrical or semi-elliptic prisms (4a, 4b) being opposed in the sense of height along an axial separation plane so that the respective semicircular or semi-elliptic lower bases lie on said orthogonal fourth plane composing together a full circle or a full ellipse, respectively; wherein said end portion, said second portion and said two prisms (4a, 4b) are integral with each other. at a first end along said longitudinal axial direction, an end portion defining a flat circular or elliptical corneal applanation surface, having a respective applanation radius or semi-axis, arranged on a first base plane of the end portion orthogonal to a longitudinal axis of the tonometer head, and having a second base parallel to said flat corneal applanation surface; a second portion, distinct from said end portion and integral with it, having a respective major base having a second radius or second semi-axis and arranged on a second plane orthogonal to said longitudinal axial direction, and a respective minor base along a third cross section arranged on a third plane orthogonal to said longitudinal axial direction and having a third radius or third semi-axis smaller than said second radius or second semi-axis, respectively, said second portion having a respective external lateral surface comprised between said major base and said minor base, at least a zone of said external lateral surface being inclined with respect to said corneal applanation surface by a respective internal angle comprised between 0° and 80° and being configured to define a rectilinear light path so that a light shaft incident on the external lateral surface from outside of the applanation head enters said second portion and propagates in said end portion up to said flat corneal applanation surface without to be reflected and without encountering material discontinuity surfaces; two semi-cylindrical or semi-elliptical prisms (4a, 4b), each having: - a respective semicircular or semi-elliptical lower base integral with said second portion and arranged along a fourth plane orthogonal to said longitudinal axial direction; - a nominal height at a center of the respective semi-circular or semi-elliptical lower base; - a semi-elliptical upper base surface opposite to said respective lower base and inclined with respect to the lower base by a respective internal angle comprised between 10° and 60°; - a respective semicircular or semi-elliptical lower base integral with said second portion and arranged along a fourth plane orthogonal to said longitudinal axial direction; - a nominal height at a center of the respective semi-circular or semi-elliptical lower base; - a semi-elliptical upper base surface opposite to said respective lower base and inclined with respect to the lower base by a respective internal angle comprised between 10° and 60°; said two semi-cylindrical or semi-elliptic prisms (4a, 4b) being opposed in the sense of height along an axial separation plane so that the respective semicircular or semi-elliptic lower bases lie on said orthogonal fourth plane composing together a full circle or a full ellipse, respectively; wherein said end portion, said second portion and said two prisms (4a, 4b) are integral with each other.