Contact Lenses-How They Work And How I Fit Them Part II

Rigid Lenses

As their name suggests, “Rigid Contact Lenses” are made from a stiff material which maintains its shape when the lens is placed on the cornea. Because of this fact, these lenses provide superior optics in many situations. These lenses are made with a CNC lathe which allows me to design some very custom and very complex lens designs. These lenses can have several different curves across the back surface of the lens, which improves the fitting relationship between the lens and the cornea. In the “bad old days”, rigid lenses had one curve across their back surface, making it difficult to have the lens align precisely with the cornea. Using cutting edge technology, I can now design lenses that precisely follow the cornea’s contour, greatly improving not only lens comfort but also lens stability.

I can also design very precise optics on the front side of the lens, allowing my to correct high degrees of astigmatism, and even irregular astigmatism. Rigid bifocal lenses can also be designed with total control over the size, location and power of the distance, near and intermediate vision zones in the lenses. This allows me to fit even the most complex cornea and visual systems with multifocal lenses. I also use these lenses to perform “vision rehabilitation” for patients with significantly irregular astigmatism or post refractive surgery vision problems such as glare, halos, irregular astigmatism and double vision. You can learn more about this on my website “Better Vision Correction”.

Soft Lenses

These lenses are made from soft, pliable material which drapes over the surface of the cornea, creating a comfortable lens fit, but with a few more limitations on the type of vision that they can correct. These lenses have come a long way during my years in practice. They now come in designs to correct myopia, hyperopia and astigmatism as well as bifocal lens designs. Among soft lenses, there are many different materials used, some which are designed to only be used once and disposed of (Daily Disposable Lenses), some designed to be replaced after two weeks of wear and some designed to be replaced after a month of wear. I rarely fit lenses designed to be used for more than a month. 99% of the time that I fit a lens designed to be used for more than a month, it is a very expensive custom designed astigmatic correcting lens.

Shorter lens life spans has greatly reduced the number of contact lens related eye health issues that I see. Frequent lens replacement doesn’t mean that a lens cannot create a complication, but replacing lenses more frequently prevents lenses from becoming dirty and deposited which reduce both the lenses ability to move oxygen to the cornea and increase the likelihood of both infection and allergic reaction to the lens.

Soft astigmatic lenses have two powers in them, typically one that is oriented pretty much vertically and one that is oriented horizontally. These two powers are always 90 degrees away from each other in orientation. These lenses are designed to not rotate on the surface of the eye using one or more lens design techniques. This keeps the two focal powers of the lens oriented correctly on the eye. If the lens does rotate a bit on the surface of the eye, the orientation of the powers in the lens is altered to compensate for the lens rotation. There are microscopic lens orientation marks inscribed on the front of these lenses so that I can see how the lens is positioning and moving on the eye. You can see these markings on the image below:


Choosing Which Type Of Lens To Fit

I base my lens type recommendation to my patients based on many factors. The first is ocular health. If there are any specific ocular health issues to deal with such as a pre-existing corneal degeneration or dystrophy, known ocular allergies, dry eye or eyelid anomaly, my choices may be limited to one type of lens (soft or rigid) and if a soft lens, a specific lens replacement schedule may be much preferred. Patients with significant ocular allergies often times do much better with daily disposable lenses for example. Once the patient and I have talked about the “Soft vs Rigid” decision, I then start thinking about which type of lens material, replacement schedule and lens design will provide the best combination of ocular health and vision correction. If we are going to use a soft lens, I will typically select trial lenses for the patient to wear for a few days to a few weeks and after insuring that the patient knows how to handle and manage their lenses will see the patient back in a few days to a few weeks. If I am designing rigid lenses, I will use the patient’s prescription (the glasses and contact lens Rx’s are usually different, sometimes quite a bit different) to design their initial lenses. I say initial lenses because I may need to modify the fit and power of the lenses to maximize lens comfort and vision. Here is a link to an interesting video about the rigid lens design process that I use.

In the next and final segment of this project, I’ll cover what I look for during contact lens follow up visits and discuss some of the lens complications that I see and how I deal with them. As always, feel free to drop me an email or set up a free, no commitment consultation by calling the office.

Dr. Warren

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