Prescribing for Presbyopia
Scleral Multifocal Power Profiles
BY CRAIG W. NORMAN, FCLSA
Similar to a comparison of the optical properties of aspheric GP multifocals previously discussed in this column (Norman, 2014), researchers Kargenian, Kindt, Rosen, and Pole from the Michigan College of Optometry followed up by performing a similar evaluation titled “Power Profiles: A Scleral Multifocal Analysis,” which was presented at the 2016 Global Specialty Lens Symposium as a scientific poster (www.pentavisionevents.com/ckfinder/userfiles/files/Scleral%20MF%20NIMO%20Poster%20v6.pdf).
Many manufacturers offer scleral lenses with multifocal optics. The purpose of this study was to analyze the surface power profiles in two different distance powers of various scleral multifocal lens designs by measuring them with the Nimo TR1504 contact lens power mapper, manufactured by Lambda-X SA.
Thirteen different scleral multifocal contact lens designs (26 lenses in total) were ordered, with one ultimately excluded due to breakage in shipment. Diameters ranged from 14.0mm to 18.0mm, distance powers were +3.00D and –3.00D, and all lenses were ordered as a +2.00D add. Some lenses contained center-near (CN) optics, while others were center-distance (CD). All had a 7.50mm base curve (45.00D) and had similar sagittal heights.
Lens material was determined by the manufacturer, and index of refraction and center thickness were accounted for in the TR1504 calculations.
Power profiles (Figures 1 and 2) were created along the 180° meridian to provide a visual interpretation of the transition of power from the optical center to an 8.0mm zone diameter in the plus powered lenses.
Figure 1. Center-distance plus lenses.
Figure 2. Center-near plus lenses.
Results showed that although the ordered distance powers of the lenses were identical, the resulting measurements varied, especially in the CN designs. For example, lens 13 and lens 25 are both CN plus lenses, but their power profiles differ significantly. Also, note the difference in power profiles between the CN and CD configurations.
Scleral multifocal contact lenses aim to provide presbyopic patients with optimal vision at distance and near. But, unlike corneal GP designs that all translate during changes in position of gaze, sclerals perform more like soft contact lenses such that the multifocal optics remain in front of the pupil at all times.
The authors’ conclusions are that not all scleral designs are created the same, reaching the full add power at different points on the lens. This demonstrates the importance of communicating with your laboratory to fully understand how each presbyopic scleral lens is designed and in what situations each may best be used for your patients. CLS
For references, please visit www.clspectrum.com/references and click on document #244.
Craig Norman is Director of Research, Michigan College of Optometry at Ferris State University. He is a fellow of the Contact Lens Society of America and is an advisor to the GP Lens Institute. He receives honoraria from Bausch + Lomb and Truform Optics. You can reach him at CraigNorman@ferris.edu.