Improving Vision With PRK For Keratoconus
For years, PRK has been avoided with keratoconus. PRK had the potential to make the keratoconus worse!
But recently things are starting to change. It isn’t that the PRK procedure has changed, it’s that our ability to treat keratoconus has improved. Specifically, a procedure called corneal cross linking was developed to stabilize and prevent keratoconus from getting worse.
Today, PRK can be used in conjunction with corneal cross linking in order to help improve vision with keratoconus. In addition, newer technologies such as topography-guided treatments also allow for a more personalized correction to reduce distortions caused by keratoconus. While there are still some limitations with PRK for keratoconus, it can be a helpful way to improve vision.
The Problems In The Past With PRK
In the past, the concern with PRK was that the procedure could weaken an already weak cornea. During PRK, a special laser is used to reshape the cornea and correct vision. This is done by precisely removing small amounts of corneal tissue.
The trouble with laser eye surgery when it comes to keratoconus is that if you remove too much of the cornea and thin it out, the cornea won’t be as strong. For those with keratoconus and even those with borderline or subclinical keratoconus, this means that laser eye surgery such as PRK or lasik can cause the cornea to become even weaker. This is known as post-laser eye surgery ectasia (or a progression of the keratoconus).
As the cornea becomes weaker, the cornea changes shape and as the cornea changes shape and becomes irregular and distorted, vision becomes worse.
Because of this, laser eye surgery was avoided whenever keratoconus was suspected.
Corneal Cross Linking
But even without having laser eye surgery, corneas with keratoconus get worse over time.
So to prevent that from happening, an additional procedure was developed called corneal cross linking. This procedure combines a special eye drop with UV light to link the cornea together and make it stronger.
And this procedure works! Corneal cross linking is able to prevent additional loss of vision from keratoconus.
Also check out How Good Is The Corneal Cross Linking Success Rate?
But How To Improve Vision?
The primary goal of corneal cross linking is to prevent the keratoconus from getting worse; which is also good at preventing the vision from getting worse.
Keratoconus causes the cornea to become severely distorted. As the keratoconus and cornea gets worse the vision gets worse (see also Breaking Down The Stages Of Keratoconus & What You Experience).
But corneal cross linking isn’t designed to improve vision.
So early on after cross linking was developed, surgeons have tried to figure out how to use laser eye surgery combined with corneal cross linking to reduce those distortions and improve vision.
When keratoconus reaches a certain stage, standard glasses and contact lenses become less effective at correcting vision. Standard glasses and contact lenses can’t correct the distortions in the cornea. The cornea shape is just too irregular.
Normal laser eye surgery works the same way. A normal treatment only works well for regular corneas.
But over time, a different laser treatment was developed, called topography-guided treatments.
Unlike traditional laser eye treatments, topography-guided treatments provide a custom treatment pattern based upon the individual cornea. A complete map is taken of the cornea to identify the irregular and distorted shape. Extra lasers pulses are then applied in order to smooth out those distortions to create an even and regular shape.
This means reduced distortions and better vision. This is great!
But using topography-guided PRK for keratoconus isn’t as straightforward as it may seem. Even when done in conjunction with corneal cross linking. There are still certain limitations to correcting vision with keratoconus. And still lot to learn about the best way to perform these treatments.
Thinning the cornea
The biggest reason PRK hasn’t always been done for keratoconus is that thinning the cornea can make the keratoconus worse. Corneal cross linking does change the equation. But in general many still tread cautiously.
After-all, it would ruin the point to treat with PRK if it would just make the cornea worse. Fortunately, limited long-term data show that this works.
But to reduce the risk of PRK weakening the cornea, less prescription is treated with the PRK. Less prescription means removing less corneal tissue.
This may mean that PRK can’t effectively get rid of all the prescription. In some cases, this means that topography-guided PRK is used just to improve the distorted cornea and improve vision WITH glasses or contact lenses.
There is more to be learned how much treatment can effectively done with corneal cross linking.
And while topography-guided PRK treatments work great, you still may not be able to have completely perfect vision; even with glasses and contact lenses. Much of that depends on how bad your keratoconus is.
PRK treatments are able to treat a certain amount of distortions on your cornea. If the distortions are too high, PRK may only be able to reduce them instead.
Corneal cross linking itself can change the prescription
When the cornea becomes weaker, it changes shape. But the same thing can happen when you strengthen the cornea back up again. Some of the change in shape can reverse. Not all of it, but a noticeable amount.
This can lead to a significant change in prescription after just corneal cross linking. Learn more about it at Does Cross Linking Improve Vision?
While this is generally good, it can make treating that prescription with surgery more difficult. It’s hard to treat a changing prescription. This changing prescription becomes more important when PRK is performed closely or at the same time to the cross linking procedure.
Because of this, many will wait until the prescription has stabilized first before performing a PRK treatment. This can take a year or two after cross linking! Waiting this long, however, can improve the results of the PRK treatment.
Performing PRK on a cornea already treated with cross linking still comes with its own challenges. There can be some variability in how the laser interacts with the strengthened cornea. In addition, there is still much more to be learned about long term results.
How is all this solved? Only time will tell. While only one method of cross linking is approved for use in the United States, different protocols are being invented to improve cross linking; some of which may cause less changing prescription over time.
Treating keratoconus with PRK is an evolving field.
What once was risky in the past for keratoconus patients has now become an option thanks to the development of corneal cross linking. By strengthening the cornea and reducing the chance that the cornea can get worse with time, the door is open to correct vision with PRK. Modern topography-guided PRK treatments can also improve the distortions on the cornea caused by keratoconus to improve vision beyond what can be done with standard glasses and contact lenses. Despite all these advancements, there is still more to be learned.
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