Plaque Simulator's 3D plaque models include the toroidally shaped structures of the suture eyelets. The coordinates on the exterior surface of the sclera which underly the doughnut hole in the eyelet can be expressed as a meridian clock hour (in the manner of the retinal diagram) and a chord distance along that meridian measured from the limbus. Plaque Simulator automatically calculates the scleral coordinates underlying each eyelet of a plaque and the chord distance between eyelets. Manual calculation and/or verification of these coordinates and distances are also supported.

To use the coordinates, the surgeon marks the coordinate meridians on the eye near the limbus. The chord distances are measured using a Castroviejo caliper as illustrated on the right. The chord distance between the eyelets helps to confirm that the meridians have been correctly projected posteriorly from the limbus.

In reference to the earth, meridians are lines of longitude which are expressed as degrees offset from the prime meridian that passes through Greenwich in the United Kingdom. In reference to the eye, meridians are also lines of longitude, except that they are expressed as clock hours on the retinal diagram.

The retinal diagram is a 2D polar map of the entire spheroidal surface of the retina with the posterior pole at the map's center. The tic marks on the retinal diagram illustrated to the right are spaced 1 mm apart. Note that the circumferential distance between these marks increases with radial distance from the pole at the center of the diagram. The outermost circle on the diagram is the limbus. The diameter of the limbus circle appears to be much greater than the diameter of the equatorial circle. In 3D space, however, the diameter of the limbus is actually much smaller than the diameter of the eye at its equator.

In Plaque Simulator, the retinal surface is modeled as being 1 mm inset from the exterior surface of the sclera. An outline of the plaque, which rests against the exterior of the sclera, is projected onto the retinal surface. In the example on the right, we see that the holes in the eyelets are centered along the 1:00 o'clock and 2:52 o'clock meridians.

The chord distance from the limbus to the exterior sclera underneath an eyelet can be measured by passing a meridian plane through the eyelet in the 2D planar Dosimetry window. The illustration to the right is the 2:52 o'clock meridian. The meridian plane can be advanced from eyelet to eyelet by simply clicking the Eyelet button or by control-clicking the button to display a contextual menu from which a specific eyelet can be selected. If the adjacent Ruler tool is enabled the distance from the limbus to the scleral suture point below the eyelet will be plotted.

The Ruler tool can also be dragged manually to measure arbitrary chord distances anywhere in the window. Option-clicking the Ruler button automatically moves one end of the ruler to the limbus and the other end to the suture point below the most recently selected Eyelet. Distances to the limbus are calculated automatically and displayed on the retinal diagram for convenience along with the meridian hour (e.g. 2:52,4.5mm). The manual tools in the Dosimetry window enable you to confirm that the automatic calculation is working correctly. The suture points are also displayed three dimensionally in the Patient Setup window.

A list of suture eyelet coordinates for each plaque is printed at the lower left corner of the Retinal Diagram document. A list of distance(s) between eyelet pairs, measured on the exterior sclera, appears near the upper right corner. In the example to the right, the distance between eyelets A and B measured on the exterior sclera is 9.3 mm. The coordinates also appear adjacent to each eyelet in the diagram itself.