An ophthalmic instrument for use with a subjects eye, comprising an interferometer having a test arm in which the subjects eye is to be positioned and a reference arm, the reference arm including a mirror adapted to be positioned such that the reference arm has a predetermined length, and an ophthalmic apparatus coupled to the interferometer such that, by altering a test arm length, a length between the ophthalmic apparatus and the eye is also altered. The mirror is positioned to achieve the predetermined length and a length of the test arm is adjusted such that interference between the light reflected from the eye and the light reflected from the mirror is achieved, the ophthalmic apparatus is optically aligned with the eye.
