Gas permeable lenses dominated much of the 70's and 80's, but lost significant ground in the last 2 decades with the advancement of soft lenses. Most contact lens specialists prefer to fit Gas Permeable lenses (GPs) over soft lenses due to the excellent optics of the lenses, longevity, and corneal health benefits. Patients on the other hand typically have rejected them due to the initial discomfort of the lenses.
Until recently, GPs have been primarily designed with only 3 or 4 curves in the lenses. Your doctor would take a small 3mm measurement of the center of your cornea, and then ask the lab to create a GP lens of anywhere from 8-9.5mm in size. How have we measured the rest of the cornea to fit the GP lens you might wonder? Simply put, we guessed, ordered the lens, checked the fit, and then made a series of one or many adjustments until we found we had the appropriate fit.
The problem with fitting gas permeable contact lenses, is that we are often trying to adjust the back curvature of the lens, to optimize the tear "lens" between the contact and the cornea. This tear lens however, is invisible to us whenever the size decreases below the 20um level. Another issue we have when designing gas permeable lenses are the manufacturer's limitations on fabrication. Many labs have basic lathes that can only cut a 3 or 4 curve lens, however some of the most sophisticated labs have lathes that have the potential to cut hundreds of curves over the surface of the lenses. Unfortunately most of those labs don't utilize the full capability of the lathes, and still cut the traditional 3 and 4 curve lenses of the past.
With WAVE contact lenses we can now create hundreds of curves on a single lens which allow for a more optimal fit with better tear coverage and corneal alignment. We are fortunate enough to work with a fantastic lab that has the ability to produce these lenses.
With all the technology necessary and difficulty in fitting the gas permeable lens, why would we bother to do so? This is often a question I get from soft contact lens wearers who aren't familiar with any other modality. There a multiple reasons why corneal gp lenses can be a much better option than soft contact lenses.
Vision - Its very difficult to find a soft contact or even a spectacle lens that can compete with the fantastic vision offered by a well fit corneal gas permeable lens. This is due to the fact that the GPs correct the irregularities of the cornea with amazing thin lens tear optics. The tears that fill in behind the lens and the cornea create a custom refracting surface which "sphericalizes" the corneal surface, creating a near perfect refracting lens.
Health - Corneal GP lenses are typically the most healthy option for the eye as well for a multitude of reasons. One of the most important aspects of corneal health that is often ignored by many practitioners is the area of the limbal stem cells just on the periphery of the cornea. These stem cells are responsible for constantly healing the surface stress of the cornea on a daily basis. Soft lenses typically hug the limbal stem cell area and can cause compression and oxygen deprivation. Because GP lenses typically are smaller in size than the cornea, they do not exert pressure on the limbal stem cells.
Comfort - Yes, without a doubt, soft lenses are initially much more comfortable than gas permeable lenses upon insertion. However, given a few days and weeks in corneal gas permeable lenses, most patients will report great comfort. In my experience, it is much more common for patients to complain about dryness with their soft lenses than those patients who wear gas permeable lenses. After the initial adaptation period with GP lenses, most patients will not complain about comfort and can wear their corneal lenses comfortably for most of the day.
If you haven't tried contacts in a while, or have been unhappy with your soft lenses and would like to consider trying GP lenses, feel free to mention it to either myself or Dr. Giedd at your next appointment and we'd be glad to discuss it with you further.
See better and live better,