Myopia progression and axial elongation after refractive surgeries remains a concern for all refractive surgeons, which are contrary to common sense and worthy of attention. However, there are few reports on the progression of adulthood myopia, before or after surgery. In this study, we mainly discussed the refractive stability of ICL implantation for adult myopia correction and the risk factors for myopia progression after surgery, which can provide insight into adulthood myopia progression.
In agreement with previous studies14–17, the results of this study also showed that ICL implantation is a safe and effective procedure for myopia correction. High myopic and ultra-high myopic patients can obtain superior visual results after ICL implantation, yet post-operative axial elongation and myopia progression is inevitable in some cases. Therefore, it is of clinical interest and significance to understand the refractive stability, axial length changes and their risk factors in the high myopia population undergoing ICL implantation.
In this study, the mean axial elongation rate for all the patients was 0.03 mm/year. Gaurisankar et al's 5-year follow-up study showed that the mean axial elongation rate was 0.04 mm/year, being slightly higher than that of our study.22 When examining the younger adults (20 to 40, mean, 21.6 years) in their study, Lee et al found that the myopic progression rate was −0.24 to −0.28 D/y and the axial elongation rate was 0.06 to 0.07 mm/year.23 Both myopic progression and axial elongation was faster compared to our study, most likely due to a well-established fact that the refractive state is relatively unstable in younger adult myopia population.
A large number of previous studies24–26 have shown that the main environmental factor for myopia progression in children is the competitive lifestyles and heavy schoolwork. It is generally believed that the myopia will tend to stabilize after adulthood, but pathological myopic patients still have the possibility of myopia progression into middle age.27,28 Pathological myopia is a kind of disease characterized by persistent axial elongation, asymmetric posterior scleral thinning, and posterior scleral staphyloma. This pathological process will lead to myopia progression, as well as macular splitting, choroidal neovascularisation, retinal atrophy and other fundus complications, resulting in irreversible visual impairment.29–33 Many studies have confirmed that fundus lesions in high myopia are closely related to axial elongation, and axial length is positively correlated with fundus damage. The shorter the axial length, the lower the incidence of fundus damages. With continuous axial elongation, the retina and choroid gradually become thinner, Bruch's membrane breaks and choroidal neovascularisation may occur.28,30 The current study showed that the myopia progression in adults was related to their preoperative ocular biometrics and not related to age and gender. The patients with higher myopia and longer axial length were prone to myopia progression, especially those with myopia higher than -12.0 D and axial length longer than 28.00 mm. For these patients, surgeons should fully communicate with them before surgery, inform them of the possibility of myopia progression and the risk of fundus complications in the long-term after surgery, and follow them up closely after surgery. If necessary, posterior scleral reinforcement can be considered to slow the axial elongation.34,35
Interestingly, we found that the axial length in some of the patients tended to shorten after ICL implantation. The axial length measured by partial coherence interferometry (PCI) represents the optical distance from the anterior surface of the cornea to the retinal pigment epithelium layer along the optic axis, which can be affected by choroidal thickness.36 It has been shown that the choroidal thickness after ICL implantation became significantly thicker than that before surgery, especially in the foveal and nasal areas.37,38 Therefore, we speculate that the increase of choroidal blood flow and the thickening of the choroid may have lead to the shortening of the axial length measured by PCI in the current study.
This study has a few limitations. The sample size is relatively small, and the follow-up time is relatively short for studying adulthood myopia. In addition, this study population is the adult myopia patients after ICL implantation rather than the general myopia population. Therefore, the conclusion of this study cannot be readily extrapolated to the overall myopic population.
In conclusion, our study found that ICL implantation is a safe and effective surgical method. Adult patients with higher preoperative myopia and longer axial length have a higher possibility to experience continuous axial elongation and myopia progression after refractive surgery, especially for those with myopia higher than -12.0 D and axial length longer than 28.00 mm.