CORNEAL LASER: THE 5 MOST IMPORTANT FACTORS TO CONSIDER BEFORE SURGERY

Corneal Laser Refractive Surgery has become commonplace in 2020. However, one should still consider some crucial points before deciding to undergo surgery.

1. Procedure Options and Laser Type

Excimer lasers perform LASIK and PRK/Trans-PRK procedures but only the Schwind Amaris can perform no-touch Trans-PRK. No other laser platform has SmartSurface technology. Studies are showing superior results with Trans-PRK versus PRK. The main reason for this is the quicker recovery but other contributing factors include a smoother ablation surface and better discomfort scores. There are, however, some specific indications for PRK. On this platform I shall refer to Trans-PRK as substitute for both Trans-PRK and PRK procedures.

Femtosecond lasers perform SMILE procedures only.

Trans-PRK

Trans-PRK is the most versatile procedure as the least amount of tissue is changed.  In addition, individualized custom ablation profiles contribute to this fact. We refer to the amount of tissue ablated as the percentage of tissue altered (PTA). Hence, even some of the thinnest of corneas can tolerate a Trans-PRK very safely, and subsequently Trans-PRK is the procedure with the lowest risk profile. There is no limiting factor in diameter size because a flap is absent.

The only drawback is the slightly prolonged recovery time. In my experience, most of my patients have had functional vision immediately after the procedure and normal vision by day four.  Other surgeons have had the same experiences. The image quality improves after this as the epithelium undergoes remodelling. I tell my patients that recovery is about a week, but they should expect improvement up to a month. However, improvement is possible up to six months after the procedure.

LASIK

LASIK has been the standard procedure of choice for most surgeons for routine cases. Many surgeons exclusively do LASIK and avoid PRK. Some large centres have switched to Trans-PRK since it’s inception. The speedy recovery and the pain-free experience are the significant gravitas towards LASIK. Unfortunately, no matter how experienced or competent a surgeon is, there are still flap complications. Also, the flap adds to the PTA, and therefore thinner corneas contraindicate to this technique. These thinner corneas form a small part of the average population. Myopia, hyperopia and astigmatic errors can be corrected. Custom ablation profiles are possible. LASIK is a widely performed and safe surgery in 2020.

SMILE

SMILE is an excellent procedure for moderate to high myopia without high astigmatism. Currently, there are no hyperopia profiles possible with this technology. Custom ablations are not possible, and astigmatism is permissible but for lower errors than Trans-PRK. Top-up procedures are dangerous.  The major positive is the quick recovery and excellent visual results. As the corneal tissue is transparent, and the amount of tissue removed is minimal in low myopes, doing this procedure has a high risk for smaller errors. The risk is the same for ectasia as with LASIK in higher error procedures. As there is no flap, it has some advantages over LASIK. But with the Femtosecond laser comes other specific complications like suction loss and it’s associated problems.

Would I perform this procedure if I had a Femtosecond laser? Absolutely as it is incredibly safe with excellent results. Do I think it is necessary to have a Femtosecond laser specifically for this procedure? No. There is no current literature-based advantage to this procedure in risk or results profiles above the other two options, while it increases the cost of the process. Consider the fact that we are in a resource constraint environment.

Which option would I choose?

If safety is the most significant concern, then Trans-PRK without a doubt.  I am a microsurgeon and need pristine vision. For all refractive errors other than moderate to high myopia, I would opt for Trans-PRK. For moderate to high myopia, I would consider all three options. If quick recovery is of utmost importance, then I would opt for LASIK or SMILE. If price is not an issue, then SMILE is an excellent option depending on availability and surgeon preference. LASIK has been and still is an excellent procedure for routine cases.

Summary

There is very little difference in these procedures in terms of visual outcome with the systems available. There is a definite advantage to the Trans-PRK versatility and safety profile. If the slightly slower recovery (three days) were not present with this procedure, we would all be doing it on every patient. Why don’t all surgeons offer Trans-PRK? They do not have the laser to provide this modern treatment modality.

2. Corneal Thickness

Often the corneal thickness determines the procedure type. Usually, surgeons have a default surgery, whether it be SMILE, LASIK or Trans-PRK which they utilize for most cases. The most versatile of these options is, of course, the Trans-PRK as the PTA is the lowest. Thin flap LASIK (100-micron flap) is now possible with Femto-LASIK and modern microkeratomes and have broadened the range of corneas for LASIK. Literature has shown no advantage between LASIK or SMILE for the development of ectasia.

3. Refractive Error

Please note that almost all the laser systems available have shown excellent results. It is when comparing specific results between systems that some lasers outperform others.  To add to this, differences in outcomes are often clinically irrelevant.

Myopia or nearsightedness has shown to be the best profile to laser with normal vision in 98% on day one after LASIK. This statistic is with the Schwind Amaris. Myopia correction results is this good for the simple fact that surgeons remove a regular disc of tissue.

Historically, hyperopic ablation profiles regress. Regression could be resulting from the remodelling of the epithelium as a doughnut of tissue is taken. The second most widely accepted theory is that surgeons often undertreat hyperopes because of their inherent lenticular tone. Nevertheless, with the newest SmartSurface technology that can extend the size of the ablation, regression is less, and higher hyperopic correction is possible than before.

Astigmatism profiles are excellent. Again, the Schwind Amaris has shown the best correction with the least residual error present post-ablation.

4. Corneal Laser and Keratoconus

Keratoconus is a type of ectasia which causes thinning and progressive conical shape formation. It is an absolute contraindication for refractive surgery. For a subset of these patients, higher-order aberrations results in loss of best-corrected vision. Custom ablation profiles can address these aberrations. We are in the beginning stages of setting up protocols for these profiles as it carries a high risk for further disease. To add to this, adjunctive corneal crosslinking prevents ectasia.

As our corneal lasers improve even further, our options to enhance this subset of patients will also improve. Laser corrective surgery is an exciting treatment modality in this terrible blinding disease.  Currently, we are proceeding with extreme caution.

5. Corneal Laser and Age Considerations

There are only a few contraindications for operation, and hence patients between the ages of 18 and 50 should qualify for corneal refractive surgery. Patients above 50, one has to consider the lens and presbyopia status.

Presbyopia and cataract formation is the dividing factor for lens versus corneal refractive surgery. Below the age of 50, we quickly opt for corneal surgery because we know that the patient should enjoy at least ten years of excellent vision before the development of cataracts. After the age of 60, we seldom do primary corneal refractive surgery because we know that the patient will be developing cataracts within a short few years. The lens surgery options available in presbyopic patients also gives us more options to manage refractive problems. We weigh up all possibilities including the number of surgeries, presbyopia correction and presence of cataracts.

Please note, however, that there is no upper limit to corneal laser surgery. Anybody that would like to be spectacle free, no matter the patient’s age or lens status could qualify for surgery. Therefore, a refractive surgeon needs to have a look and decide.

Conclusion

ONLY a refractive surgeon can decide whether corneal laser surgery is possible or not and the risks involved for you as an individual. The uninformed will look for reasons to stop you from having surgery.

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