An optical measurement apparatus comprising: an optical system comprising: a source arranged to generate, when in use, a probe beam (116, 118), the optical system being arranged to direct, when in use, the probe beam (116, 118) to a location to be measured, the location to be measured being a location of a feature of an eye having a first axis and a second axis; a detector arranged to receive, when in use, a reflected beam from the location to be measured; and a receiving axis; wherein the apparatus further comprises: a processing resource operably coupled to the detector and capable of assessing when in use, a characteristic of an output signal generated by the detector, assessment of the characteristic of the output signal corresponding to an assessment of degree of alignment of the location to be measured with the receiving axis of the optical system; wherein the output of the detector has a signal profile corresponding to a reflection of the probe beam (116, 118) in respect of the location to be measured, characterised in that the output signal is a trace comprising a number of profiles corresponding to a number of reflections of the probe beam (116, 118); and the processing resource is arranged to use the trace to assess the degree of axial alignment of the first or second axis with the receiving axis of the optical system. an optical system comprising: a source arranged to generate, when in use, a probe beam (116, 118), the optical system being arranged to direct, when in use, the probe beam (116, 118) to a location to be measured, the location to be measured being a location of a feature of an eye having a first axis and a second axis; a detector arranged to receive, when in use, a reflected beam from the location to be measured; and a receiving axis; wherein the apparatus further comprises: a processing resource operably coupled to the detector and capable of assessing when in use, a characteristic of an output signal generated by the detector, assessment of the characteristic of the output signal corresponding to an assessment of degree of alignment of the location to be measured with the receiving axis of the optical system; wherein the output of the detector has a signal profile corresponding to a reflection of the probe beam (116, 118) in respect of the location to be measured, characterised in that the output signal is a trace comprising a number of profiles corresponding to a number of reflections of the probe beam (116, 118); and the processing resource is arranged to use the trace to assess the degree of axial alignment of the first or second axis with the receiving axis of the optical system. a source arranged to generate, when in use, a probe beam (116, 118), the optical system being arranged to direct, when in use, the probe beam (116, 118) to a location to be measured, the location to be measured being a location of a feature of an eye having a first axis and a second axis; a detector arranged to receive, when in use, a reflected beam from the location to be measured; and a receiving axis; wherein the apparatus further comprises: a processing resource operably coupled to the detector and capable of assessing when in use, a characteristic of an output signal generated by the detector, assessment of the characteristic of the output signal corresponding to an assessment of degree of alignment of the location to be measured with the receiving axis of the optical system; wherein the output of the detector has a signal profile corresponding to a reflection of the probe beam (116, 118) in respect of the location to be measured, characterised in that the output signal is a trace comprising a number of profiles corresponding to a number of reflections of the probe beam (116, 118); and the processing resource is arranged to use the trace to assess the degree of axial alignment of the first or second axis with the receiving axis of the optical system. a processing resource operably coupled to the detector and capable of assessing when in use, a characteristic of an output signal generated by the detector, assessment of the characteristic of the output signal corresponding to an assessment of degree of alignment of the location to be measured with the receiving axis of the optical system; wherein the output of the detector has a signal profile corresponding to a reflection of the probe beam (116, 118) in respect of the location to be measured, characterised in that the output signal is a trace comprising a number of profiles corresponding to a number of reflections of the probe beam (116, 118); and the processing resource is arranged to use the trace to assess the degree of axial alignment of the first or second axis with the receiving axis of the optical system.