Contact Lens Design & Materials
Contact Lens Design & Materials
Multifocal Scleral Lenses
BY RONALD K. WATANABE, OD, FAAO; JENNIFER LIAO, OD; & SHANNON BLIGDON, OD
Scleral lenses continue to grow in popularity both for regular and irregular corneas. For presbyopic patients, this usually has meant wearing reading glasses over their lenses, which may be an acceptable option for those enjoying the excellent distance vision and comfort that scleral lenses deliver. But now, several scleral lens manufacturers offer multifocal versions of their designs, an added bonus for presbyopes who rely on scleral lenses whether or not they have irregular corneas.
Due to the immobile nature of a well-fit scleral lens, multifocal scleral lenses are simultaneous vision designs, with disadvantages similar to those of most soft multifocals.
Patients simultaneously view through distance, intermediate, and near powers in the multifocal design, somewhat decreasing that image quality across all distances, more so with higher add powers. Pupil size and lens positioning can also significantly impact visual performance. A few parameters are critical to provide optimal vision.
Most multifocal scleral lenses are center-near designs with front-surface multifocal optics. They all accomplish this in different ways. Here are few examples.
Onefit (Blanchard) has an aspheric transition zone between a spherical central near zone and a peripheral distance zone, which minimizes the shadow effect often associated with center-near designs. Dominant and nondominant eyes have slightly different designs that are not pupil size dependent.
DigiForm (TruForm Optics) is also a front-surface, center-near design. The standard near zone size is 2.0mm but can be specified larger or smaller in 0.2mm steps. The add power can be specified based on patients’ needs. Toric and quadrant-specific back surfaces are also available for those who have significant corneal toricity or irregularities.
Maxim and Comfort SL (Accu Lens) are front-surface, center-near designs with optic zones that are pupil size dependent. The near zone for the dominant eye’s lens is smaller and ranges from 1.4mm to 3.6mm. For the nondominant eye, the near zone ranges from 1.9mm to 4.1mm. Add powers are generally specified +0.50D more than the spectacle add power. The Maxim lens is used for irregular corneas, while Comfort SL is indicated for non-distorted corneas and can be ordered empirically.
Custom Stable Near (Valley Contax) has center-near zone parameters that are fully customizable using the proprietary Vision Range Delivery System. The near zone on the front surface is determined based on pupil size and eye dominance. Typically, it is designed to be half the pupil size on the dominant eye and two-thirds of the pupil size on the nondominant eye. Toric options are available with this lens.
The AVT Scleral Multifocal (Advanced Vision Technologies) has a center-distance design with the multifocal optics cut into the back surface of the lens, in contrast to the designs above. It has a central spherical distance zone that transitions into an aspheric intermediate zone and a full add zone. There is a distance zone ring at 6.0mm to help with nighttime distance glare and flare common with multifocal designs as the pupil dilates. The lens is available in a toric design as well.
Expanding multifocal options mean that more presbyopic patients will be able to enjoy their scleral lenses without having to use reading glasses. Though patients will have to adapt to simultaneous vision, education and appropriate design adjustments can result in many satisfied presbyopic scleral lens wearers. CLS
Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a Diplomate in the American Academy of Optometry’s Section on Cornea and Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass. You can reach him at email@example.com. Drs. Liao and Bligdon are currently residents in Cornea and Contact Lenses at the New England College of Optometry.
Contact Lens Spectrum, Volume: 28 , Issue: November 2013, page(s): 21