Sclerals for Dry-Eyed Presbyopes
By Edward S. Bennett, OD, MSED, FAAO
Today there are essentially four options for correcting presbyopia with contact lenses: overspectacles, monovision, and soft and GP multifocals. Noting that tear volume decreases with age, a contact lens correction that provides satisfactory vision, good initial comfort, and that minimizes dry eye-related symptoms and signs with this age group is certainly the goal.
The frequent replacement of soft multifocals is a benefit for dry eye patients, and these designs continue to improve in their ability to provide acceptable vision at all distances; however, there are still issues of less-than-optimum optical quality and pupil-dependent simultaneous vision optics, typically with a center-near design.
GP multifocal designs provide the best quality of vision of the latter three options (Rajagopalan, et al, 2007); however, in a soft lens-dominated society there can be a certain level of reluctance to fit GP lenses, especially for longtime soft lens wearers.
However, if presbyopic patients are experiencing dry eye symptoms and desire initial comfort that may rival that of their current soft lenses, a scleral multifocal design may represent the best option in 2012 and beyond.
Multifocal Scleral Designs
Several multifocal scleral designs are now available in the United States, with more soon to come. TruForm Optics has two designs available. The DigiForm Lens is an up to 16mm corneal-scleral lens with five condition-specific designs. TruForm also offers the DigiForm 18 lens, an 18mm design with diagnostic etchings on the front surface of the trial lenses indicating which curves can be adjusted in the event that there is too much or too little clearance at those areas. DigiForm lenses are available with either a center-near multifocal design with adjustable zone and add powers or with a center-distance design surrounded by a near band of add power that then returns to distance. TruForm recommends using one of its fitting sets to establish the correct lens for the patient, after which the lens will be manufactured with the multifocal add-on.
For the So2Clear Progressive corneal-scleral design (Art Optical/Dakota Sciences/Metro Optics), you can use the standard So2Clear fitting set and then order the presbyopic version. It has a center-near multifocal design with a standard 2.0mm center-near zone that ranges from 1.0mm to 6.0mm in 0.05mm increments. Add powers are +1.00D to +3.50D in 0.25D steps.
Lens Dynamics (Firestone) offers both the Dyna Semi-Scleral (13.5mm to 16.0mm diameter) and the Dyna Scleral (17.0mm to 19.0mm diameter) designs. The Quad Sym edge design and front toric powers are available if needed, as well as a front-surface aspheric treatment with add powers up to +2.50D.
Blanchard Contact Lens is currently working on a center-near multizone design with aberration control optics. In addition, Advanced Vision Technologies (AVT) is introducing a unique back-aspheric center-distance scleral multifocal. Available in a standard (but adjustable) 16.1mm diameter, the back surface of the design has reverse curves to accommodate the limbal zone.
Although scleral multifocal lens designs have been limited until just recently to center-near optics due to a lack of translation, the optical quality should result in better overall quality of vision compared to soft multifocals. Future clinical research will focus on comparing multifocal scleral initial comfort and vision to that of soft multifocal lenses. This would be especially important to compare in a borderline dry eye population. CLS
Acknowledgements: Jean Blanchard (Blanchard Contact Lens), Don Dixon (TruForm Optics), Mike Johnson (Art Optical), Keith Parker (AVT), and Al Vaske (Lens Dynamics/Firestone).
For references, please visit www.clspectrum.com/references.asp and click on document #200.
|Dr. Bennett is assistant dean for Student Services and Alumni Relations at the University of Missouri-St. Louis College of Optometry and is executive director of the GP Lens Institute. You can reach him at firstname.lastname@example.org.|