Abstract: A system and method of measuring a tissue structure is provided. The method includes obtaining image data of the tissue structure. Also, an anatomical landmark in the image data is identified. A first geometric shape is applied to the image data of the tissue structure based on the anatomical landmark. For example, the geometric shape may have a linear portion, such as a square or diamond. The method also includes applying a second geometric shape to the image data of the tissue structure based on the anatomical landmark. The second geometric shape may be different than the first geometric shape, such as an arc or parabola. The method also includes segmenting a first substructure of the image data from a second substructure of the image data. These substructures may be, for example, a sclera and ciliary body of an eye.