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ISSN : 1229-6457(Print)
ISSN : 2466-040X(Online)
The Korean Journal of Vision Science Vol.27 No.2 pp.137-146
DOI : https://doi.org/10.17337/JMBI.2025.27.2.137

Factors Influencing Long-term after Corneal Refraction Correction Surgery

Won-Kyu Kim1), Jung Un Jang2)
1)Dept. of Optometry, Graduate School, Eulji University, Student, Uijeongbu
2)Dept. of Optometry, Eulji University, Professor, Seongnam
* Address reprint requests to Jung Un Jang (https://orcid.org/0000-0002-2475-315X) Dept. of Optometry, Eulji University, Seongnam TEL: +82-31-740-7491, E-mail: jju@eulji.ac.kr
May 19, 2025 June 29, 2025 June 29, 2025

Abstract


Purpose : This study aimed to investigate the factors influencing myopic regression in individuals who had undergone corneal refractive surgery at least one year prior.



Methods : We conducted a study on 44 adults aged 20 years or older who had undergone corneal refractive surgery at least one year prior. Subjective and objective refraction tests, distance and near phoria tests, AC/A ratio, corneal irregularity measurement (CIM), and higher-order aberrations were measured.



Results : There were no significant differences in myopic regression among groups based on distance and near phoria, AC/A ratio, and trefoil aberration, nor was there a significant correlation with myopic regression (p>0.050). However, older age and longer postoperative duration were significantly associated with higher myopic regression (p<0.050). In terms of corneal irregularity (CIM), the normal CIM group exhibited significantly higher myopic regression than the abnormal CIM group (p<0.050). Coma aberration was also significantly higher in the normal coma group compared to the abnormal coma group in both eyes (p<0.050). Regarding spherical aberration, a significant difference was observed only in the right eye, where the normal spherical aberration group had significantly higher myopic regression than the abnormal group (p<0.050), whereas no significant difference was found in the left eye (p>0.050).



Conclusion : This study aimed to investigate the factors influencing myopic regression after corneal refractive surgery. The results showed that myopic regression progressed more significantly with increasing age and longer postoperative duration. Additionally, lower corneal irregularity (CIM), coma aberration, and spherical aberration were associated with greater myopic regression.


AC/A ratio , CIM , Corneal Refractive Surgery , Heteroptoria , Higher-Order Aberration , Myopic Regression

각막 굴절교정 수술 후 장기적인 측면에서 영향을 미치는 요인

김원규1), 장정운2)
1)을지대학교 대학원 안경광학과, 학생, 의정부
2)을지대학교 안경광학과 교수, 성남

    Ⅰ. Introduction

    Corneal refractive surgery is a procedure designed to correct nearsightedness or myopic astigmatism, for individuals who prefer not to wear glasses or contact lenses. The two most common types of corneal refractive surgery are LASIK and LASEK. While most patients report satisfaction with their vision following LASIK, several side effects can complicate daily life. These include glare, light flashes, myopic regression, and decreased visual acuity. Among these side effects, myopia regression is a phenomenon where the improved vision after corneal refractive surgery diminishes over, typically within one to six months. Myopia regression after surgery often causes inconveniences such as the need for reoperation or the need to wear glasses or contact lenses again.1),2)

    Previous studies have shown that people with a high AC/A ratio are prone to excessive accommodative convergence during near work, which may increase the risk of myopia regression in the long term.3) Studies on refractive surgery have reported an increase in higher-order aber- rations in both men and women after refractive surgery, with coma aberration values reported to be higher in myopic individuals.4) Additionally, studies related to aberrations have reported that coma aberration and spherical aberration increase as myopia progresses. Furthermore, it has been reported that higher-order aberrations are associated with increased corneal irregularity and reduced structural stability of the cornea following corneal refractive surgery.5,6) Currently, several known causes of myopic degeneration include increased stromal thickness, regeneration of corneal flaps, preoperative myopia, and lifestyle factors.7) However, few studies have examined whether various factors, such as corneal irregularity (CIM), higher aberrations or near and far phoria, and AC/A ratio, which may influence myopia progression over the long term in adults and children who have not undergone keratorefractive surgery, also affect myopia regression following keratorefractive surgery. Therefore, it is essential to conduct a comprehensive evaluation of various factors to analyze the causes of myopia regression more accurately. To determine whether myopia regression occurs, it is ideal to measure and compare the refractive error immediately after surgery with the changes in refractive error over time. However, reports indicate that corneal refractive surgery is generally more frequently performed with overcorrection, resulting in some hyperopia, rather than undercorrection with residual myopia, in order to prevent long-term regression.8) It has also been reported that visual acuity stabilizes approximately six months after keratorefractive surgery.9) Based on this, we assumed that the refractive state was hyperopic immediately after surgery and conducted a study on patients who had undergone keratorefractive surgery more than one year. Therefore, the aim of this study was to examine the long-term effects of myopia regression in individuals who had undergone keratorefractive surgery more than a year after surgery and to provide useful references for patient management.

    Ⅱ. Material and Subjects

    1. Subjects

    In this study, 22 males and 22 females aged 20 years or older, who had undergone corneal refractive surgery for at least one year, agreed to the purpose of this study and were willing to participate. Those with a perfect correction of -0.50 D or more were classified as having myopic degeneration, and those with and without myopic degeneration were categorized into two groups. Patients were excluded if they had amblyopia, suppression, strabismus, vertical emmetropia greater than one prism, had undergone more than two corneal refractive surgeries, had ocular or systemic diseases, or were taking medications that could affect vision. All protocols and testing procedures were approved by the Institutional Review Board of Eulji University (EU 24-30), and all subjects were informed orally and in writing about the purpose of the study, testing methods, and possible side effects.

    2. Method

    1) Measurement of higher order aberrations and corneal topography

    Higher order aberrations were measured using the I-Profiler 3.0 (Carl-Zeiss, Meditec, Jena, Germany). Corneal topography, Corneal Irregularity measurement, and nighttime spherical, coma, and trefoil aberrations were measured. Based on Chen's 2017 study, spherical aberrations of less than 0.21 μm were classified as normal spherical aberrations and those of more than 0.21 μm as abnormal spherical aberrations.10) The coma aberration was classified as normal coma aberration if it was less than 0.26 μm and abnormal coma aberration if it was more than 0.26 μm, and trefoil aberration was classified as normal trefoil aberration if it was less than 0.19 μm and abnormal trefoil aberration if it was more than 0.19 μm.

    2) Refraction

    Objective refraction was measured using Auto Refractive Keratometry (HRK-8000A, Huvitz, Korea). The subjective refraction was then fully corrected using a projected acuity table (HCP- 7000, Huvitz, Korea). The Dominant eye was measured using the Hole in the Card method.

    3) Phoria Test

    After full correction, the phoria test was performed at a distance of 5 meters in the distance and 40cm in the near. Horizontal phoria was measured using the Howell phoria card test method, with a separating prism of 6△ BD joined to the right eye. According to Morgan's criteria, distance ortho was graded from 0 to 2△ exophoria, and near ortho was graded from 0 to 6△ exophria and categorized as exophoria, ortho, or esophoria.11)

    The vertical phoria test was measured using the Maddox Rod test method, with the Maddox placed vertically on the right eye. Patients were excluded if they had vertical phoria of more than 1 prism.

    4) AC/A ratio

    AC/A ratio was measured using the calculated AC/A ratio, and after AC/A ratio measurement, the patients were categorized into normal AC/A ratio, high AC/A ratio, and low AC/A ratio based on Morgan's normal range threshold of 4±1 (△/D).12)

    3. Data Analysis

    The SPSS 21.0 (SPSS Inc., Chicago, IL, USA) program was used to analyze the collected data. Frequency analysis and descriptive statistics were performed to determine the general characteristics of the study subjects. Comparisons of means between subjects with myopic degeneration and those without myopic degeneration were performed using independent t-tests and one-way analysis of variance. The significance level of all data was p<0.05.

    Ⅲ. Result

    1. General characteristics

    The mean age of the 44 adults aged 20 years or older who were at least 1 year post-corneal refractive surgery was 36.18±1.50 years, with 22 males and 22 females. The mean refractive error was -0.22 D±0.80 D in the right eye and -0.21 D±0.79 D in the left eye. Distance phoria, near phoria, and AC/A ratio were 1.22±2.71△ exophoria, 5.84±5.36△ exophoria, and 4.50± 1.65, respectively. Corneal irregularity (CIM) was 1.62±0.60 in the right eye and 1.66±0.73 in the left eye, and spherical, coma, and trefoil aberrations were 0.31±0.25, 0.32±0.23, and 0.15± 0.09 μm in the right eye and 0.32±0.28, 0.35± 0.26, and 0.15±0.10 μm in the left eye, respectively (Table 1).

    2. Factors Affecting Myopia Regression

    1) Age and Myopia Degeneration

    A one-way analysis of variance was performed on age and myopia regression. In both the right and left eyes, the 20-year-old group had significantly lower myopia than the 30-year-old and over 40-year-old groups (p<0.001), and the difference between the 30-year-old and over 40-year-old groups was not significant.

    Post hoc analysis of group differences (Scheffe) showed that in the right eye, the groups were 20s, over 40, and 30s, while in the left eye, the groups were 20s, 30s, and over 40(Table 2).

    2) Postoperative period and myopia regression

    An independent t-test was performed to analyze the time elapsed since surgery and myopia regression. The results showed that myopia was higher in the group with more than 5 years in both the right and left eyes, and the difference was significant (p<0.050)(Table 3).

    3) Distance and near phoria and myopic degeneration

    Independent t-tests were performed for distance phoria and myopic degeneration, near phoria and myopic degeneration, and esophoria, ortho, and exophoria groups. When comparing the esophoria and ortho groups, there was no significant difference between the groups in both distance and near for both the right and left eyes (p>0.050). Similarly, when comparing the Esophoria and exophoria groups, there was no significant difference between the groups at both distance and near for both the right and left eyes (p>0.050). The comparison of the ortho and exophoria groups also showed no significant difference between the groups for both the right and left eyes (p>0.050) (Table 4).

    4) AC/A Ratio and Myopia Regression

    Independent t-tests were performed for AC/A ratio and myopic degeneration, comparing the low AC/A ratio, normal AC/A ratio, and high AC/A ratio groups. Comparing low AC/A to normal AC/A and low AC/A to high AC/A groups, there was no significant difference between the groups in either eye (p>0.050). The comparison of normal AC/A to high AC/A ratio also showed no significant difference between the groups in both eyes (p>0.050) (Table 5).

    5) Corneal Irregularity (CIM) and Myopia Regression

    Independent t-tests were performed for corneal irregularity and myopic regression. The analysis showed that both eyes had higher myopia in normal corneal irregularity than in abnormal corneal irregularity. The difference between groups was significant only in the right eye (p<0.050) and not in the left eye (p>0.050)(Table 6).

    6) Higher aberrations and myopic degeneration

    Independent t-tests were performed for spherical aberrations, coma aberrations, and trefoil aberrations on myopia regression. The analysis showed that in spherical aberrations in the right eye, normal spherical aberrations had significantly higher myopia than abnormal spherical aberrations (p<0.050), while in the left eye, there was no significant difference between groups (p>0.050). In coma aberrations, both eyes showed higher myopia in normal coma aberrations than in abnormal coma aberrations (p<0.050). Trefoil aberrations showed no significant difference between groups in either eye (p>0.050)(Table 7).

    Ⅳ. Discussion

    Currently, the primary known causes of myopic degeneration include increased corneal stroma thickness, regeneration of corneal flaps, and lifestyle factors, all of which are known to contribute myopic degeneration.6) In this study, we analyzed the effects of age, postoperative period, phoria, AC/A ratio, corneal irregularity, and higher aberrations on myopia regression, in addition to previously reported factors. The results indicated that as patients age, the longer the time since surgery, and the greater the myopia regression, the more progressive the myopia. A 2021 study by Lee also reported that adults in their 20s and early 30s may develop myopia due to an increase in axial length of the eye, which can lead to myopia progression.13) Furthermore, Biswas' study reported that a lack of outdoor activities and increased near work may contribute to adult myopia. 14) Based on this, it is thought that the higher myopia in the older age group (30s and above) is higher than in the 20s group due to an increase in the length of the ocular axis with age, as well as the increased time spent working at close range in modern life. Additionally, since most corneal refractive surgeries are performed in the 20s, the age of the patient increases over time following surgery. Consequently, both age and time since surgery are likely factors that influence myopia regression. Therefore, it is recommended that patients improve their lifestyle habits by reducing the time spent on close work and increasing outdoor activities to reduce the risk of long-term myopia regression. For Phoria and the AC/A ratio, we did not find a significant association with myopia regression. In previous studies, neither distance nor near phoria affected myopia regression, and the AC/A ratio did not show a significant difference in myopia between groups.15),16) Donald's study also reported that while high AC/A ratios may contribute to the development of myopia, they do not affect the rate at which myopia progresses.3) This suggests that while esophoria and high AC/A ratios cause a lot of accommodation and convergence in the eye, it is not enough to have a significant effect on myopia progression in the long term.

    In terms of corneal irregularity (CIM), myopia was found to be higher in normal CIM compared to abnormal CIM in both eyes. It was expected that more irregularity and a more regenerating cornea would result in greater myopic degeneration with greater irregularity, but in fact, myopia was higher with normal irregularity. This suggests that irregularity is higher when the amount of corneal ablation is high immediately after surgery, but as the cornea regenerates, irregularity decreases, resulting in higher myopia in eyes with lower irregularity.17) For this reason, it is thought that myopia regression was more advanced in the group with lower corneal irregularity in this study, but to determine the exact cause, it is essential to observe and analyze the amount of corneal cuts at the time of surgery, the degree of corneal irregularity, and changes in corneal thickness over time in follow-up studies. For higher aberrations, spherical and coma aberrations showed higher myopia in normal spherical aberrations compared to those with abnormal spherical aberrations, while trefoil aberrations showed no significant difference in myopia between the groups. Previous studies have shown higher myopia in those with normal ranges of aberrations, and Lim's study reported that coma aberrations increase in the negative direction as refractive error increases in the (-) direction.17),18) This is likely because coma aberration and myopia are inversely related. While increasing aberrations may reduce visual quality, they do not directly influence myopic degeneration. In this study, certain factors had a similar impaction myopic degeneration in both the right and left eyes, while other factors seemed to affect only one eye. This suggests that the degree of myopia degeneration may vary depending on the structural characteristics of each eye and the individual's habits regarding eye use. Generally, many studies have analyzed the right and left eyes together, as it is assumed that the physiological characteristics of both eyes are similar and that there is no significant difference in myopic degeneration between them.19) However, since the myopic degeneration in each eye after surgery may vary based on the physiological characteristics of the eye and pattern of visual use, it is essential to analyze the right and left eyes independently to account for these individual differences in future studies.

    Ⅴ. Conclusion

    The results of this study showed that as patinets age, the longer the time since surgery, the more myopia progressed, the lower the corneal irregularity (CIM), and reduced spherical and coma aberrations are associated with increased myopia regression. Therefore, factors such as age, time since surgery, corneal irregularity (CIM), spherical aberration, and coma aberration may serve as predictive of myopia regression in the long term. Future studies should analyze the relationship between myopia regression and lifestyle habits, including the number of hours spent on near work and time spent outdoors, as well as the extent of corneal cutting during surgery and changes in corneal thickness and irregularity before and after surgery.

    Figure

    Table

    Characteristic of the subjects

    Refractive Error(D)† : Spherical equivalent(S.E.) value of refractive errors.
    Heterophoria(△)* : exo (-), eso (+)

    Comparison of mean myopic regression and age

    Comparison of mean myopic regression by the postoperative period

    Comparison of mean myopic regression by phoria

    Comparison of mean myopic regression by AC/A ratios

    Comparison of mean myopic regression by CIM

    Comparison of mean myopic regression by higher aberrations

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