contact lens materials
Who Needs High-Oxygen Transmission Contact Lenses?
BY NEIL PENCE, OD, FAAO
Silicone hydrogel lens materials are widely recognized as a significant advancement in regard to oxygen transmission. However, higher levels of oxygen haven't solved all lens-related complications, and interesting debates can arise regarding the role of oxygen in dry eye, inflammation or infection.
Who Benefits the Most?
For extended or continuous wear, high-oxygen materials are an obvious requirement. For daily wear we often question the oxygen amount needed. It's likely that many daily wear patients do occasionally fall asleep with their lenses on. There are also many patients who wear their lenses every waking hour, meaning their corneas are covered by the lenses or the eyelids for years on end. While the need for high oxygen may not be as obvious, many daily wear patients benefit from the increased oxygen transmission of silicone hydrogels.
Patients with high ametropia also benefit from higher oxygen transmission. For comparative purposes, oxygen transmission values are typically reported based on the levels found through a –3.00D lens. Any lens power or design that has significantly different thickness than a –3.00D lens will have much less oxygen transmission than the reported level. This generally means high-minus lenses, medium-to-high plus lenses and toric lenses.
Custom Silicone Hydrogels
With all lenses, companies must decide available power ranges based on manufacturing and inventory costs compared to expected demand. Custom lenses are basically those parameters that would not be profitable for the company to maintain inventories. A +12.00D or a –18.00D lens is not likely to be needed often, but as noted, few wearers benefit more from a high-oxygen transmission lens than do patients needing high powers. Fortunately, there are custom silicone hydrogel lenses from CIBA Vision.
The O2Optix Custom is a lathe cut version in a material that's only slightly modified from the O2Optix sphere. It's available from –20.00D to +20.00D in the diameters and base curves listed in Table 1, and it's intended for quarterly replacement. You can order a single lens either empirically (the 8.4mm/14.0mm is an average starting point) or on the advice of the company's consultation department. Then order the yearly four-pack after evaluating fit and performance and refining acuity with an over-refraction.
Others who benefit from the O2Optix Custom are those patients needing a smaller or larger lens diameter. Pediatric fits and instances when a pinguecula might interfere with the lens edge can benefit from the 13.2mm lens. When a patient might benefit from a larger diameter than that of standard silicone hydrogel lenses, it's nice to remember that a 14.8mm lens is available.
More for (Almost) All
With currently available silicone hydrogel lenses, you can offer most patients the higher oxygen these lenses allow. For those outside the standard parameters, high-powered spherical lenses are now possible with the O2Optix Custom lens.
We hope more custom silicone hydrogel lenses will be introduced to fit astigmats whose needs are outside currently available parameters. Then we can truly offer high oxygen for all our soft lens patients. CLS
Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana.