In relation to the eye, topography usually refers to corneal topography – this is the measurement of the surface of the cornea. The cornea, the clear window that makes up the front of our eye, works like a fixed-focus lens and actually does the majority of the light focusing in our eye. Irregularities in the corneal surface can have dramatic impact on vision. Corneal topography can be used to measure and map out the corneal surface, similar to mapping out a mountain range in a topographical map. Aberrations like astigmatism can be detected, as can higher-order irregularities such as keratoconus.