This study revealed that 100% as well as 70% of participants had UCVA of ≥ 6/9 and ≥ 6/6 respectively at three months post-operation. These findings were similar to the observations of Kazutaka et al,13 who reported that 100% of eyes had UCVA of 20/20 and 20/40 respectively but slightly different to the observations of Chuck et al 10 who reported that 70% and 92% of participants had UCVA of 20/20 and 20/40 at 12 or more months post-operation following PRK. The similarity seen between this study and kazutaka et al,13 may be due to the fact that both studies included myopic spherical equivalent less than or equal to -10 D, unlike the report by Chuck et al 10 which included myopic spherical equivalent greater than − 10 D. Very high levels of myopia (greater than − 10 D) is a risk factor for under correction, high regression rates, low efficacy and loss in best corrected visual acuity following keratorefractive surgery.11 Furthermore, the longer follow up period as well as difference in the type of keratorefractive surgery may contribute to the disparity between this study and the observations of Chuck et al.10 This study also revealed that 100% of eyes treated were within ± 1.00D of attempted correction.
Loss of CDVA of two lines or more in this study was 0% which was comparable with the findings of Alper et al.11 Regarding cylindrical refraction, this study showed under correction, similar to the findings by Zhang et al12 and Chan et al14, but correction index of 0.65 ± 0.14 from this study was lower than that reported by Zhang et al (0.97 ± 0.3)12 and Chan et al (0.98 ± 0.08)14. This can be attributed to the fewer number of participants in this study compared to theirs. A larger number of participants will be needed to have a true reflection on the state of cylindrical refractive correction.
In terms of stability, no significant refractive regression was found from day 1 to 3 months after keratorefractive surgery in this study. This is similar to the findings of Kazutaka et al.13 However, the long-term refractive stability of keratorefractive surgery cannot be concluded at this time, since the follow up period was for 3 months. Alper et al.11 found statistically significant trend of regression in their study on outcome of SMILE in high myopia, with achieved spherical equivalent of -0.26 D, -0.33 D, and − 0.43 D at 1,3, and 5 years, respectively. This may be due to high regression rates associated with high myopia as compared with the low to moderate myopia.
In this study, two eyes (20%) developed postoperative diffuse lamellar keratitis and one eye required a surgical intervention. At 3 months post-operation, the eye that had further surgical intervention lost one snellen line due to astigmatism but visual acuity was 6/9. Alper et al11 had no sight threatening complications while Kazutaka et al13 had suction loss in 3 eyes (1.2%), subconjunctival hemorrhage in 7 eyes (2.8%), transient interface haze and diffuse lamellar keratitis in 23 eyes (9.1%) and 2 eyes (0.8%) respectively, during their first postoperative month. They were monitored without additional surgical intervention, and gradually resolved. No keratectasia, epithelial ingrowth, or any other severe complications were observed in this study. Keratorefractive surgeries (SMILE and LASIK) was safe in the six participants that underwent the procedure as 60% of participants gained 1 snellen line of CDVA and 30% of participants had no change in snellen line of CDVA with absence of severe complications. Similarly, studies with longer follow-up and larger samples have also shown good safety parameters.11,13
The limitations in this study were short follow up period, small sample size for those that had keratorefractive surgery, non-randomized nature of the study. However, the results of this study could serve as a foundation for future studies on keratorefractive surgery in Nigeria as it provided information that could be useful for patients’ counseling, health planning, improving surgical uptake and advocacy as well as a better understanding of patients’ disposition to the procedure.