ABSTRACT
The Modified Preliminary Drill treats anisometropia, where the disparity between the right and left eye is −0.75 D or more. The drill also treats compound anisometropia and anisometropic amblyopia. The assumption is that patient’s prescription is within the myopic model, and the deviation took place during postdevelopment. The conditions allow for the application of an inline direct and indirect effect.
Normally, the patient attempts the Preliminary Drill first. It prepares the eye for the Modified Preliminary Drill. The conventional definition for anisometropia is a difference of at least −1.00 D between the right and left eye. In reference to what can be treated by ortho C, a disparity of −0.75 also qualifies as anisometropia.
The treatable range is when one eye is moderate (from −1.00 D to −1.75 D) while the other eye is in the midrange (from −2.00 D to −2.75 D). In that range, the treatment is optimal when the better eye is −1.00 D or −1.25 D, and the weaker eye is −2.00 D or −2.25 D. It seems that the myopic range of the better eye determines the degree of correction for both eyes. Anisometropia is another exception where the flatness of the lens is not equal to the absolute value of the prescription.
