We recently reported that it was possible to obtain a complete topographic image of human eyes by high-resolution 3D MRI.
11 We compared the contour of the inner scleral surface seen in the OCT images and the shape of the outer surface of the eye obtained by 3D MRI. We have developed software to analyze the human eye shape obtained by 3D MRI, and we used this software to automatically analyze the degree of symmetry of the posterior eye segment in the horizontal and sagittal planes. We also determined the pointedness or bluntness of the posterior pole of the eye (
Fig. 2). Briefly, the view of the eyes from six points, namely the front, back, superior, inferior, nasal, and temporal, was incorporated into the software of the 3D MRI. Then, a central axis line passing through the geometric center of the eye was automatically drawn. The point of intersection of the central axis and the posterior margin of the eye was defined as the basal point (P
b). Then, a point on the central axis 87 pixels, approximately 12.5 mm, anterior to the P
b was defined as the point of origin (P
o) of the measurements; the purpose was to avoid the influence of axial length on the location of P
o.
Next, Po was rotated 22.5° nasally in the horizontal plane, and a line was drawn posteriorly. Where the line intersected the margin of the eye was called Pn. Similarly, Po was rotated 22.5° temporally in the horizontal plane, and where the line from Po intersected the margin of the eye was called Pt. In the sagittal plane, Po was rotated either inferiorly or superiorly, and where lines intersected margin of the eye was called Pi or Ps, respectively. The area of the segment formed by Po, Pb, and Pn was defined as Sn; the area of the segment formed by Po, Pb, and Pt was defined as St; the area formed by Po, Pb, and Pi was defined as Si; and the area formed by Po, Pb, and Ps was defined as Ss. The degree of symmetry in the horizontal plane was expressed by the ratio of Sn and St, and the degree of symmetry in the sagittal plane was expressed by the ratio of Si and Ss. The posterior surfaces with ratios between 90 and 110 were classified as symmetrical.
For the sharpness of the posterior surface, the angle formed by Pn, Pb, and Pt was defined as the posterior sharpness angle. The shape of the posterior segments of the globe was defined as “pointed” when this angle was ≤150°, and the shape of posterior segment of the eye was defined as “dull” when this angle was >150°.