Construction of a 3-D atlas of corneal shape.

Purpose: A methodology is proposed to build population-based average three dimensional (3-D) atlases or standards of the human cornea based on topographic data, along with variation maps. Also, methodologies for comparing populations or screening populations, based on these atlases are proposed.
Methods: Topographies (Orbscan II; Bausch & Lomb, Rochester, NY) of 516 normal subjects were used. Methodology for the construction of a corneal atlas consisted of (1) data acquisition from both anterior and posterior corneal surfaces in the format of a 101 x 101 grid of z elevations evenly spaced (every 0.1 mm) along the x and y axes; (2) spatial normalization of the topographies on a unique average best-fit sphere to reduce the large variability in size and spatial location between corneas; (3) generation of the average 3-D model; and (4) statistics maps including average, median, and SD for each point of the grid.
Results: To demonstrate the informative potential of this methodology, examples of atlases were generated. Numerical corneal atlases allow (1) characterization of a population, (2) comparison of two or more populations, (3) comparison of an individual with a reference population, and (4) screening of a population for the detection of specific corneal shape abnormalities, such as keratoconus or previous refractive surgery.
Conclusions: The concept of a 3-D corneal atlas was developed. The proposed technique was meant to be simple, accurate, reliable, and robust and can be extended easily to any type of topographer capable of providing tridimensional corneal maps.