Purkinje imaging has been one of the most popular methods to perform phakometry. Purkinje images, first described by Purkinje in 1832, are reflections from the ocular surfaces. The radii of curvature of the different ocular components (acting as mirrors) are estimated from the relative height of images of the light source. The brightest reflection (first Purkinje image, PI) comes from the anterior corneal surface and can be used to estimate the corneal radius of curvature, as it is done in keratometry. The third (PIII) and fourth Purkinje images (PIV), from the anterior and posterior surface of the crystalline lens, are used for phakometry. Two algorithms have been proposed to estimate the radii of curvature from the relative heights of PIII and PIV: the equivalent mirror (EM) theorem method, based on the replacement of the different ocular surfaces by a single mirror (Smith & Garner,
1996), and the merit function (MF), based on a recursive method (Barry, Dunne, & Kirschkamp,
2001; Garner,
1997). Recent computer simulations of an experimental Purkinje imaging system developed in our laboratory show that the MF produced more accurate results for the posterior surface than EM (Rosales & Marcos,
2006). Early Purkinje imaging systems were based on photography (Van Veen & Goss,
1988; Wulfeck,
1955) and some versions were used to study correlations between refractive error and geometrical properties of the lens (Sorsby, Benjamin, & Sheridan,
1961). Mutti, Zadnik, and Adams (
1992) used it to study myopia and to study normal ocular development in children population (Zadnik et al.,
2004). Additional technical implementations include the use of a telecentric stop lens to capture PI, PIV, and PIII (in a slightly different plane) with no magnification changes (Phillips, Perez-Emmanuelli, Rosskothen, & Koester,
1988). This method was used to measure the refractive index with age (Garner, Ooi, & Smith,
1998; Hemenger, Garner, & Ooi,
1995), with accommodation (Garner & Smith,
1997), and the change in lens radius with accommodation (Garner & Yap,
1997).