Contribution of the ocular surface to visual optics.

The air/tear interface contributes 70% of the vergence in the eye and, because of this, even minor variations in its shape can produce significant visual deficit. Placido disc-based corneal topographers measure the precise characteristics of the corneal surface, transforming shape into color-coded dioptric power maps and topography indexes related to optical quality and specific patterns associated with pathology. Artificial intelligence-based methods are used to classify corneal topography and these are used as screening tools. Coupling corneal topography measurements with aberrometry measurements permits the display of the internal aberrations of the eye. Together, these data provide the opportunity to extend refractive correction beyond sphere and cylinder to the higher order aberrations as well.