The main focus of this study was to compare the outcomes of a specific refractive surgical modality, LASIK, after discontinuation of SCL in a large sample of patients. However, only two other studies have focused on SCL removal and refractive surgery in general[14, 15].
In recent years, many recommendations and guidelines have proposed the removal of SCL at least 3 to 14 days before LASIK, but still, there are no consensus[16, 17]. Shehadeh-Mashor et al., in their case-control study concerning the duration of SCL removal before myopic refractive surgery, have found a significant difference between the patients who removed their SCL in less than 1 day and those who removed them in more than 1 day before the PRK procedure. However, they found no significant difference between those who discontinued the SCL between 1 to 3 days and those who discontinued them for more than 3 days before PRK.
As for LASIK, literature has shown little evidence on the effect of late discontinuation of SCL before the procedure. Shehadeh-Mashor et al. found no statistical difference between the SCL discontinuation in less than 1 day, 1 to 3 days, and more than 3 days before LASIK. These results were concordant with the actual study's results, mainly that they also used a microkeratome LASIK.
Nevertheless, Fragkopoulou et al., evaluated the effect of SCL discontinuation for 7 days on LASIK outcomes in 113 patients and found a significant difference between the postoperative and target spherical and cylindrical refraction. The previously mentioned study had many limitations due to the small sample size and the lack of a control group; therefore, it was concluded that the period needed to discontinue SCL remains to be determined by further investigations.
Consequently, this actual study brings additional evidence on the safety of performing LASIK 24 hours after discontinuing SCL use, especially with the large sample of patients included compared to the previous studies and the presence of a control group.
Furthermore, it has been well documented that SCL usage, regardless of the type, causes many corneal modifications: topographic and biomechanical[19, 20]. The hypoxia caused by SCL is thought to be the primary factor in corneal layer modification, leading to corneal injury caused by keratocyte apoptosis and other complex mechanisms. Even though less severe with silicone hydrogel (siHy) SCL use, these mentioned changes could take around 2 weeks or even more to stabilize after the discontinuation of the SCL[7, 15, 19]. Thus, statistically significant, those changes did not affect LASIK safety, efficacy, and predictability in most studies where the SCL was removed between 3 to 7 days before the procedure. However, in this study, the control group was comparable to that of non-SCL wearers due to their SCL removal 1 month before the LASIK procedure, ensuring that most corneal changes and distortions, whether topographic or not keratometric, were stabilized[9, 22].
As mentioned in the results, the discontinuation of the SCL 24 hours before the procedure did not affect the visual outcomes in analogy to the outcomes of LASIK reported by other authors[23, 24]. Surprisingly, SCL wearing was even positively correlated with better LASIK and PRK results regardless of the discontinuation time (at least 24 hours) in comparison to non-SCL wearers, according to Lloyd-McKernan et al.,. Their results could be explained by the age discrepancy between both groups in the study. Moreover, SCL users who already had increased corneal surface irregularities adapted better to the induced spherical aberrations, and residual refractive error after LASIK could also be an explanation. On a side note, those results are not entirely valid in the case of this actual study because Lloyd and colleagues used femtosecond LASIK.
In this study, two antibiotics were used postoperatively: an aminoglycoside (Tobramycin) and a fourth-generation fluoroquinolone (Moxifloxacin). Thus, no signs of infectious keratitis were documented using both antibiotics despite the increased risk of keratitis caused by SCL themselves and by the corneal changes that they induce, especially in group 1.
Moreover, both SCL and LASIK are known to increase the risk of dry eyes[29, 30]. It might be convenient to predict that the SCL removal 24 hours before the surgery might predispose to an increased risk of dry eyes after LASIK, especially in long-term users. However, Schirmer's test results reported were comparable in this study. Previous similar studies did not report the incidence of post-LASIK dry eyes 24 hours after the discontinuation of SCL. The literature showed an incidence range of 20 to 50% of dry eyes after LASIK, significantly earlier, but this may also be affected by patients' education and compliance with the postoperative eye drops treatment. Long-term SCL use can be assumed as a risk factor for dry eyes post LASIK. However, the risk of developing dry eye post-LASIK may not be influenced by the SCL use with the absence of predisposing dry eye disease and lack of corneal warpage.
Consequently, screening patients for dry eyes preoperatively could help predict the risk of dry eyes postoperatively. Eventually, this study may confirm that the variation in the duration of discontinuation of SCL before LASIK will not predispose patients to develop dry eyes, which can be explained by the different pathophysiology of SCL-induced dry eyes and post LASIK dry eyes[34–36].
As for intra-operative epithelial defect and corneal flap incidence, there was no statistical difference between both groups; therefore, it is safe to presume that the duration of SCL removal before LASIK did not increase the risk of these complications. However, controversial evidence exists on the effect of the duration of SCL-use wear (years) and epithelial defect requiring further investigations[37, 38]. Last but not least, no further complications like limbal bleeding, non-infectious keratitis, or central toxic keratopathy were reported.
Like other studies, this one had its limitations. Since it is a retrospective and non-randomized study; a double-blinded, randomized clinical trial with a large enough sample size should be done, or even a prospective study would also be a good start; it would give more evidence on the specific duration needed for discontinuation of SCL before LASIK. Additionally, another previously-mentioned confounding factor that was not controlled in this study is the duration of SCL use (long-term or short-term users); it could also affect LASIK outcomes due to the induction of a different spectrum of morphologic corneal changes.
Furthermore, topographic follow-up and reporting with cut-off limits and values would have added another dimension to this study and would have given more information for future patient selection recommendations. Moreover, higher-order aberrations (HOA) assessment after LASIK were not reported in this study or any other study to assess the effect of late SCL discontinuation. Thus, the groups may differ regarding HOA measurements despite having the same refractive outcomes.
The LASIK flap creation in this study was done using a microkeratome. Another study using femtosecond LASIK and even the new SMILE procedure would also be of use for future recommendations on SCL removal.
Finally, the removal of SCL 24 hours before the LASIK procedure is considered an unusual practice in refractive surgery. However, it did not negatively affect the outcomes and safety of the procedure. It remains to be seen if these results could be duplicated in prospective studies.
While it looks safe and efficient, also it has better patient satisfaction; this particular practice is not recommended or included in the guidelines. Therefore, a case-by-case selection process is recommended to be done by an expert refractive surgeon. Moreover, it is advised that refractive surgeons select their patients carefully, ensuring that Schirmer's test, break-up time test, and other routine tests are within usual international standards before performing LASIK within 24 hours of SCL discontinuation.