Breaking Down The Stages Of Keratoconus & What You Experience
Keratoconus is a progressive condition. This means that gradually over time keratoconus can get worse. What this also means is that keratoconus can exists in various stages: early in the beginning all the way to advanced or severe.
Because of this continuum of progression, various classification systems have been developed in order to stage the keratoconus. The most popular and one of the oldest being the Amsler-Krumeich classification system. But it isn't the only one. More systems have been developed to take advantage of advances in the way we can detect keratoconus.
All these classification systems are cool, and allow us to compare one keratoconus patient to another. Staging can be helpful to organize the timeline of keratoconus.
But the “stage” of the keratoconus doesn't directly influence how the keratoconus is treated. It also doesn't describe to you what you'll actually experience with your vision.
So this is what this article will cover. I'll first cover the “numbers” that define the stage, but more importantly I'll cover what you can actually expect at that stage. How well or how poorly you can expect to see, how vision can be corrected and how the keratoconus is treated.
How Does The Grading Work?
The Amsler-Krumeich classification system relies on 3 different measurements:
- How steep the cornea is (called the maximum keratometry reading)
- How thin the cornea is
- How nearsighted and how much astigmatism there is
When a cornea changes shape from keratoconus, it goes from a dome-like shape to a cone-like shape. The cornea becomes steeper.
As the cornea becomes steeper, there is a greater amount of surface area. Just like how a balloon thins as it expands, the cornea becomes thinner as it bulges out.
Finally, having a steeper cornea increases the amount of nearsightedness. As the irregular cone forms in the cornea, it adds extra astigmatism to vision.
Thus all of these three measurements increase as the keratoconus gets worse.
Newer ways to classify
Because of improvements in the way machines can measure our cornea, newer classification systems such as the Belin ABCD can rely on a few more advanced measurements:
- How steep the front of the cornea is
- How steep the back of the cornea is (a measurement that just isn't possible with older technology)
- How well vision can be corrected with glasses
- And still include the thickness of the cornea
This newer classification systems also includes a Stage 0 since our ability to detect keratoconus earlier and earlier has improved.
But for simplicity sake and to align with the most common classification system, I'll start at Stage 1.
Note: Because everyone's eye is different and because keratoconus exists on a spectrum, measurements can sometimes span two different stages. For example, if you have a very thick cornea to begin with, it won't become as thin as someone who started with thinner corneas.
Stage 1 - This can be considered mild keratoconus
Max Keratometry < 48 D
Corneal Thickness > 500 um
Myopia and Astigmatism < 5.00 D
Stage 1 of keratoconus; on the left is a map showing the curvature (known as keratometry) of the cornea, on the right is a map showing the thickness of the cornea.
Vision can still be corrected well with glasses and / or contact lenses. You may not even be aware something is wrong with your vision. You just need a higher prescription to correct it.
Stage 1 keratoconus should be treated with corneal cross linking, ****especially if progression is detected. This procedure creates bonds within the cornea to strengthen it up and can prevent the keratoconus from getting worse and causing blurry vision.
Because the vision still can be corrected well at this stage, its ideal to catch and treat keratoconus at stage 1 (or even earlier). At any age.
Stage 2 - This can be considered moderate keratoconus
Max Keratometry - 48 to 53 D
Corneal Thickness - 400 to 500 um
Myopia and Astigmatism - 5.00 to 8.00 D
Stage 2 of keratoconus
The keratoconus starts to become more symptomatic. It may start to become challenging or impossible to correct vision all the way to 20/20 with glasses or contact lenses.
But in addition to blurry vision, the irregular cone from keratoconus starts to create extra distortions in vision. This causes halos, glare and even double vision or ghosting of images.
At Stage 2 keratoconus, special rigid contact lenses may be considered (but not fully essential) to improve vision. This includes scleral contact lenses or rigid glass permeable contact lenses (RGPs).
Instead of conforming to the surface of the cornea like standard soft contact lenses, these rigid contact lenses are able to mask the irregular cone of keratoconus and prevent the cone from distorting vision. This sharpens and improves vision.
But before being fit with these special contact lenses, corneal cross linking should be performed (if not already) to stop the progression of keratoconus. And corneal cross linking will cause a change in the prescription of the eye, which will change the prescription of these special contact lenses.
Stage 3 - I would label this as severe keratoconus
Max Keratometry - 54 to 55 D
Corneal Thickness - 300 to 400 um
Myopia and Astigmatism - 8.00 to 10.00 D
Stage 3 of keratoconus
At this stage, vision CAN'T be corrected well with glasses or contact lenses. Vision is severely distorted and blurred.
Those special rigid contact lenses (scleral contact lenses or RGPs) become essential to sharpen vision.
Stage 3 is the last stage that can be treated with corneal cross linking. Beyond this stage the cornea becomes too thin to do a safe treatment.
Corneal cross linking uses UV light to create those special bonds within the cornea. Excess UV light can damage certain structures of the eye. On the inside of the cornea is a delicate layer of cells. The job of these cells is to pump water out and keep the cornea clear and transparent.
When the cornea has a sufficient thickness, not enough UV light can penetrate through and effect those cells. But too thin and excess UV light can reach and permanently damage those cells.
Stage 4 - Since we've already passed severe keratoconus, I would consider this end-stage keratoconus
Max Keratometry > 55 D
Corneal Thickness < 300 um
Myopia and Astigmatism - unable to measure
Central corneal scars present
Stage 4 of keratoconus
Vision is very poor. Vision can't really be corrected very well at all. The cornea may have scars in the center of the cornea further limiting vision and even prevent vision from being able to be fixed with those rigid contact lenses.
The cornea is too thin for corneal cross linking. But even if it wasn't, scarring in the cornea may make it a moot point anyway since there isn't much vision left.
There is really one treatment for end-stage keratoconus - a corneal transplant.
During a corneal transplant, the damaged keratoconus cornea is removed and replaced with a donor cornea. This new cornea is then stitched in placed.
Corneal transplants are unique amongst all transplant surgeries. All other transplant surgeries require medication for life to prevent the rejection of the transplant. However, the cornea doesn't! Because the cornea doesn't have any blood vessels, the immune system can't reach the new cornea very easily. Thus, the donor transplant doesn't need to be matched to the recipient and many transplant recipients can eventually get off all medications.
After a transplant, there is still a large chance of prescription and astigmatism. Thus, rigid contact lenses may still be required to correct vision.
Because keratoconus is progressive, it exists on a spectrum. To help us understand where we are on the spectrum of keratoconus, staging exists. Staging by itself doesn't directly influence the treatment. However, it can be useful to help categorize what you can expect from your keratoconus.
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