Some components affecting the precision of corneal thickness measurement performed by optical pachometry

With the Haag-Streit pachometer attached to a Haag-Streit 900 slit-lamp, 29 normal individuals were examined by repeated measurements on two separate days by the same observer. A statistical variance component model admitted three components of variance to be separated and estimated as SD: The biological day to day variation (0.006 mm), the variation attributed to the slit-lamp adjustment (0.005 mm), and the variation derived from the adjustment of the pachometer (0.013 mm). Knowing these components an optimum practical procedure of examination can be established.