Ophthalmology Cornea 5a4971cf Microcornea is defined as: A < 10 mm corneal diameter at bih B <13 mm corneal diameter at bih C < 10 mm axial length at bih D < 20 mm axial length at bih High-Yield Explanation Microcornea < 10 mm corneal diameter at bih. Megalocornea > 13 mm after 2 yr of age or >11.7 mm before 2 yr of age.