1. An ophthalmologic apparatus comprising: an imaging unit configured to image a cross-section of a cornea of an eye to be examined based on return light from the eye illuminated with measurement light; a measurement unit configured to measure a corneal thickness from a cornea cross-sectional image of the eye imaged by said imaging unit; and a correction unit configured to correct the corneal thickness based on a position of the cornea cross-sectional image on an imaging plane of said imaging unit.