In an ophthalmic laser system preferably intended for photoablative refractive surgery, a component apparatus that is preferably an optical coherence tomography device for measuring corneal pachymetry makes its measurement when the First and Second Purkinje reflections of the OCT probe beam are detected, otherwise, the reflection signal is not strong enough to enable the OCT measurement. The beam axis of the therapeutic laser of the system is co-aligned with the OCT-prbbe beam. When the First and Second Purkinje reflections of the OCT probe beam are detected, a signal is generated by the OCT device and sent to the eye tracker component of the system to engage the eye tracker operation. This allows for objective, automatic engagement of the eye tracker and alignment of the patient's optical axis to the treatment axis or a diagnostic beam axis.