ABSTRACT
Sometimes the patient performs the Preliminary Drill first before the Modified Preliminary Drill during the treatment for anisometropia. The conventional definition for anisometropia is a difference of −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 weaker eye predetermines the flatness factor for both lenses. The treatable range is when one eye is moderate (from −1.00 D to −1.75 D) and the other is in the midrange (from −2.00 D to −2.75 D). The treatment is optimal when the better eye is −1.00 D to −1.25 D, and the weaker eye is −2.00 D or −2.25 D. The patient needs to realize that the Preliminary Drill is temporary. It is usually performed first to prepare the eye for the Modified Preliminary Drill. You eventually have to treat anisometropia with the Modified Preliminary Drill.
According to research, the myopic shape of the crystalline lens and eyeball is not in proportion to the thickness of the ciliary muscle (Kuchem et al., 2013). The increase in tension of the ciliary muscle of the weaker eye due to near-point stress spills over onto the better eye. The ciliary muscle of the better eye neurologically inherits the same thickness. The myopic shape of the crystalline lens and eyeball of the better eye, however, is not in proportion to the thickness of the ciliary muscle.
It is better for a less intense drill (i.e., the Preliminary Drill) to relax the ciliary muscle rather than a more intense drill (i.e., the Standard Drill). The Preliminary Drill relaxes the ciliary muscle of the better eye without overcorrecting the lens or the axial length of the eyeball. Once you attend to the ciliary muscle before increasing the tension of the rectus muscles, the Modified Preliminary Drill becomes more effective when it attends to the eyeball as well as the crystalline lens.
