In the design and prescribing of contact lenses, there are two general categories: the first is the molded commodity-style lens, and the second is the custom lathe-cut contact lens. When considering custom contact lens design and prescribing, the major advantage is that this category allows eyecare practitioners to independently vary each and every parameter of the contact lens. This includes power (sphere, cylinder, and axis), add power, multifocal zone size, base curve, and overall lens diameter, all independent of the lens material.
When considering the complexity of multifocal optics and patients’ varying level of adaptation to simultaneous multifocal optics, custom multifocal soft lenses allow practitioners to precisely prescribe the sphere and cylinder power in increments as fine as 0.1D and the axis in increments as fine as 1º, depending on the manufacturer. This can be incredibly helpful in troubleshooting visually discriminating patients.
Similarly, due to their custom nature, the add power can be varied in as fine as 0.25D or even 0.1D steps. Custom soft lenses are also often available in add powers beyond +2.50D should the need arise; typically, add powers for molded commodity-style contact lenses end at +2.50D.
When determining multifocal zone size in custom soft contact lenses, there are some key differentiators. Practitioners can choose the traditional industry standard of center-near aspheric optics, or they also can specify center-distance optics. This is on top of the ability to specify the center zone size and the intermediate/peripheral zone size.
The peripheral/intermediate zone is the distance at which, in the example of a center-near aspheric multifocal, the distance power is reached and then remains at that power to the end of the overall optic zone. The rationale behind selecting a custom multifocal zone size is that it allows for custom tailoring to an individual patient’s unique pupil size.
When considering the fit of a custom multifocal contact lens, eyecare practitioners can vary the base curve in increments as fine as 0.1mm or adjust the overall lens diameter in 0.1mm increments. For those individuals who have uniquely large or small corneas or uniquely flat or steep corneas and who have struggled with traditional molded commodity-style lenses in the past, custom soft multifocal lenses may allow them to successfully wear contact lenses again.
Recent innovations in custom multifocal lens manufacturing have allowed companies to offset multifocal optics that no longer have to be in the geometric center of the lens, where they have been traditionally located. The rationale behind this is the subtle but common on-eye temporal position of soft lenses as well as of scleral lenses. Additionally, the visual axis and the pupil are commonly nasal to the geometric center of the cornea, which is the opposite direction of where the lens typically positions (as noted above). Therefore, contact lens manufacturers have created custom multifocal contact lens options that have the optical center of the lens offset nasally to counteract these challenges. In the case of soft contact lenses, this necessitates that the lens be prism ballasted to allow for correct on-eye orientation of the optics.
Several key advantages of custom soft multifocal contact lenses allow precise prescribing in an effort to optimize multifocal contact lens success. CLS