How to measure
To measure for eyes:
The size of the eye opening is the measurement you need. To do this you need a measurement tool either a ruler, measuring tape, micrometer. Take the dolls head and measure the eye opening from size
to size (corner of the eye near the nose, out toward the ear) once you have that measurement it will need to be converted to millimeters.
It is recommended to add a millimeter or two to that measurement.