Previously, there was a lack of preoperative simple geometric parameters to predict the outcome of lamellar keratoscleroplasty in patients with limbal dermoid. In this study, we found that the cornea-invaded length of dermoid was the most important factor predicting the postoperative visual acuity, astigmatism and amblyopia. The corneal limbus invaded length of dermoid was the most important factor related to postoperative scar formation.
Astigmatism and amblyopia caused by limbal dermoid are not only the indications of surgical intervention, but also the vision-threatening issues after the surgery[8]. We found that there was no significant change in astigmatism after surgery, regardless in the amblyopia group or the non-amblyopia group. These findings supported the previous reports that astigmatism induced by limbal dermoid might be due to alteration or moulding of the intrinsic structure of the corneoscleral wall when lesions formed13, 15–17. The visual acuity was improved after the operation, in line with the results of previous studies. Fan et al.18 followed up 66 children with limbal dermoid for more than one year after lamellar keratoscleroplasty. They found that there was no significant change in astigmatism. Yao et al.19 followed up 43 patients with corneal limbal dermoids (40 of whom underwentdermoid excision with lamellar keratoscleroplasty), and found that the median logMAR BCVA improved significantly after the surgery. However, there was no significant change in astigmatism postoperatively. Shen et al.13studied10 patients with corneal limbal dermoid treated by lamellar keratoscleroplasty, and found that the postoperative astigmatism of patients with preoperative astigmatism less than 6 D did not decrease significantly, while that of patients with preoperative astigmatism greater than 6 D decreased significantly. However, the extrapolation was weak to the limited sample size, and the present study, with the maximum astigmatism 6 D, could hardly be used to verify Shen et al.'s conclusions, which needed further study.
In this study, preoperative geometric parameters were used to predict the postoperative effect. Kim et al.12also used preoperative anterior segment photography of patients with dermoid to study the correlation between the ratio of various geometric parameters and the results after simple dermoid resection. They reported that the invaded angular axis of dermoid to corneal diameter ratio value was the most significant factor associated with postoperative visual acuity, amblyopia development, which was similar to our result. But they also found that the invaded angular axis of dermoid to corneal diameter ratio value was the most significant factor associated with postoperative scarring, which was different from our results. This could be explained by the different surgical methods. The vascularization and pseudo-pterygium are more likely to occur after simple removal, while lamellar keratoplasty is considered to be a better choice because it provides the excellent appearance, tectonic stability, and low risk of vascularization and pseudopterygium9, 13, 15, 20–22. Furthermore, there are many other factors influencing scar formation, including the length of dermoid invading corneal limbus, interface neovascularization, graft rejection, and so on18.
Our study used detailed values to study the relationship between preoperative simple geometric parameters and the outcome of lamellar keratoscleroplasty in patients with limbal dermoid. It is more convenient and practical for clinicians to apply. The clinicians only need to use the computer to open the preoperative digital anterior segment photographs and use the ruler tool on the computer to predict the postoperative effect of patients. To the best of our knowledge, our study was the first literature to report on the use of geometric parameters to predict the postoperative outcome of lamellar keratoscleroplasty in patients with limbal dermoid. When clinicians find that the cornea-invaded length of dermoid is too long before the operation, they should consider that patients still have amblyopia and astigmatism postoperatively, which requires regular monitoring, patient education, and amblyopia therapy after surgery. For patients with large corneal limbus invaded length by dermoid, clinicians should consider the high possibility of scar after the operation, strengthen the follow-up, detect the occurrence of complications in time, and take medication to avoid scar aggravation.
The cornea-invaded length of dermoid was the most important factor affecting the development of postoperative visual acuity, astigmatism and amblyopia. It might be that the closer the dermoid was to the optic axis, the greater astigmatism. It provides a new insight for the influence of pathological features on postoperative refraction. The corneal limbus invaded length of dermoid was the most important related factor of postoperative scar formation, reflecting that corneal limbus with wider invasion by dermoid had more defects of limbal stem cells and was easier for neovascularization. Neovascularization would more easily lead to rejection. In our study, postoperative grade 3 graft opacity (2/7) were related to graft rejection caused by neovascularization. In a multicenter study on the causes of corneal transplantation failure, Gomez-Benlloch and associates found that the failure of deep anterior lamellar keratoplasty was mainly due to ocular surface diseases, such as limbal stem cell deficiency23. This is similar to our result. Another possible reason was that the longer the corneal limbus invasion length of the dermoid was, the more needles were needed to fix the graft, which was more likely to cause suture-related complications. In the current study, 2 cases of postoperative graft opacity were caused by suture-related complications.
There are several limitations in our study. First, the geometric parameters related to dermoid were obtained indirectly. Due to the eyeball curvature, the geometric parameters obtained from the 2-dimentional photos might be different from the actual values. Second, the different corneal diameters, such as in children or in adults, might have an impact on length measurement. But the youngest age in our study was 4.3 years old. Anatomically, the corneal diameter of children over 3 years old is close to that of adults24. Therefore, the different corneal diameters in our study might have little influence on length measurement. Third, the patients in the current study were relatively older and the follow-up time was short, which might affect the prognosis of amblyopia. This study also lacked information about the preoperative and postoperative management of amblyopia. Next, we will include younger patients, extend the follow-up time, further analyze the effect of preoperative and postoperative amblyopia treatment on the long-term vision.
In a word, our study found the cornea-invaded length of dermoid was the most important factor affecting the development of postoperative visual acuity, astigmatism and amblyopia. The corneal limbus invaded length of dermoid was the most important factor affecting postoperative scar formation. The visual acuity, astigmatism and geometric parameters in patients with amblyopia were higher than those with non-amblyopia. These provide a reference for clinicians' preoperative decision-making and prognosis estimation.