The corneal morphology of the normal population is an aspheric surface. The cornea is gradually flat from the center to the periphery, and the whole is oblong oval. In clinical work, we will see various parameters that describe corneal morphology, such as Ecc value ( e value ), E value, p value, Q value ( Figure 1 ).
Fig. 1 (DEA520 Corneal Topographer-Shape Factor )
e value (Ecc value): also known as eccentricity,describes the change in curvature of the cornea from central to peripheral. Itis mainly used in the corneal contact lenses fitting.
Q value (p-1): also known as asphericity parameter, it describes the trend of corneal curvature from central to peripheral. It is mainly used in the design of aspheric IOL facets and personalized refractive surgery.
Fig. 2 (DEA520 Corneal Topographer-Aberration )