It's can be a challenge to correct vision for patients with keratoconus. Glasses and soft contact lenses often have a hard time doing the trick. So many of these patients look to vision correction surgery to try to get them out of their glasses and contact lenses. One such vision correction surgery is the Visian ICL. ICL surgery can work in some cases to correct vision (but not all cases). Let's see why:
What is keratoconus?
Keratoconus is a condition with progressive weakening of the cornea. A normal cornea exists in a dome shape. This dome shape allows for great optics and great vision. In keratoconus, the weakening of the cornea causes the cornea to turn into a cone shape over time instead.
Cornea shape with keratoconus, Madhero88, CC BY-SA 3.0, via Wikimedia Commons
Typically this cone shape forms in the bottom part of your cornea (not dead center where you are trying to look). As a result, this cone creates distortions in your vision. In the early stages of keratoconus, these distortions come in the form of extra astigmatism (astigmatism is the blur caused to vision by one direction of the cornea being flatter and one direction being steeper - like the shape of a football; light that enters the flat side of the cornea isn't focused at the same point as light that enters the steep part). When the astigmatism is roughly symmetric on both sides of the cornea, the astigmatism is said to be "regular" and is able to be corrected quite well with glasses.
But as the keratoconus gets worse, this astigmatism becomes irregular and asymmetric. Imagine if you took a football and were able to deflate and put a dent in one side of the football: this would create irregular astigmatism on the football. Irregular astigmatism creates distortions called higher order aberrations that can't be corrected well with glasses. These distortions create lots of night-time vision symptoms.
So what's the trouble with laser eye surgery for keratoconus?
Lasik corrects vision by remodeling the cornea. In this process, a certain amount of cornea tissue is removed. Prior to the surgery, the lasik surgeon evaluates your cornea to make sure it has enough thickness for the procedure. If the cornea is too thin, removing too much cornea tissue can cause it to become weak.
Keratoconus is a condition in which the cornea is already weak. In addition, as the cornea continues to become weak and form a cone, the cornea thins out more. Removing extra cornea tissue through lasik or PRK would most definitely cause the cornea to become even weaker and make the keratoconus even worse!
Note: there are situations in which PRK can be possible after strengthening the cornea through a procedure called corneal cross-linking, but those situations can still be limited.
Enter ICL eye surgery for keratoconus
The ICL is a great thought to correct vision for keratoconus patients. The Visian ICL is a corrective lens which is placed inside the eye behind your iris and in front of your own natural lens to correct vision. This lens contains your prescription and is designed to correct your vision and get you out of glasses. Except for the tiny incision to place the ICL, it works completely independent from the cornea. It won't thin the cornea out and cause the keratoconus to become worse.
There are even ICL lenses which correct for astigmatism called toric ICLs (see also What Is A Toric ICL?). In the early stages, regular astigmatism can be corrected quite well with a toric ICL for keratoconus.
Drawbacks of vision correction by ICL
- The main drawback of ICL correction is that it only works the best for the early stages of keratoconus. The toric ICL is only capable of correcting regular, symmetric astigmatism. It can't correct irregular, asymmetric astigmatism. Whatever you can correct with glasses, ICL is capable of correcting. If glasses can't correct your vision anymore, ICL is limited in what it can correct. If you have advanced keratoconus, ICL can reduce your prescription burden by getting rid of a large amount of nearsightedness, but it won't be able to get rid of distortions or night-time vision symptoms.
- ICL surgery can be a little less accurate in keratoconus. There is a chance you can have a small amount of remaining prescription left over. While this can also happen to patients without keratoconus, those patients are frequently able to get laser eye surgery to correct that residual prescription. That is typically not an option for keratoconus patients.
- Keratoconus can get worse with time. As the keratoconus gets worse, the prescription can continue to change. Prior to the ICL surgery, the cornea should be treated with a procedure called corneal cross-linking to strengthen and stabilize the cornea (and really, anyone with keratoconus should get this procedure done regardless of considering surgery or not). This procedure is designed to prevent the keratoconus from getting worse and prevent further vision loss from keratoconus.
So ICL eye surgery can be used in some limited early cases to correct vision with keratoconus. But the main limitation is that it can't correct the irregular astigmatism that keratoconus frequently causes.
If not ICL for keratoconus, then what?
There are good non-surgical specialty contact lens options to correct vision with keratoconus. There are two main types: rigid glass-permeable contact lenses and the newer scleral contact lenses. Unlike soft contact lenses which conform to the shape of the cornea, these contact lenses are rigid and are able to mask the cone from keratoconus. These contact lenses are able to restore a nice natural dome shape to your cornea again. This cuts out the irregularity and the asymmetry. Not only does this correct prescription but also dramatically eliminates the distortions and night time vision symptoms. These are a very good option for advanced keratoconus patients.
Summary
The ICL is best used for the early mild cases of keratoconus (after the cornea has been treated with corneal cross-linking). In those cases, glasses and soft contact lenses are also capable of correcting vision with minimal additional distortions. But the ICL can also be considered to help reduce the burden of glasses in advanced cases where contact lenses or glasses can't be worn for a variety of reasons. The ICL just won't be able to completely restore all vision in those cases; there will still be some irregular astigmatism and distortions.
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