The default dose reduction A(R) for reduced scatter near an air interface where R is the distance from the air boundry and d is the distance from the source are estimated from figure 8 in Thomson et al, Monte Carlo dosimetry for I-125 and Pd-103 eye plaque brachytherapy, Medical Physics, 35(12): 5530-5543, 2008. The correction factor becomes negligible at 1.5 cm from the air interface.

In Plaque Simulator the air interface is estimated as a plane through the cornea and tangent to the anterior oblate spheroid of the eye model on the AP axis of the eye.