Anterior Segment Parameter Analysis After SMILE Surgery and Its Impact on the Calculation of Effective Intraocular Lens Position

Objective: This study aims to investigate post-SMILE alterations in corneal refractive power, axial length, and anterior chamber depth, as well as examining the relationship between changes in anterior chamber depth and corneal ablation depth. By utilizing both Pentacam and IOL Master devices, researchers will input measurement data into the Holladay 1 and Haigis formulas to calculate and compare Estimated Lens Position (ELP) values. The objective is to provide accurate anterior segment parameters for patients undergoing corneal refractive surgery, thereby enhancing the precision of intraocular lens calculations. Methodology: A large hospital of Hebei Medical University made a prospective study. The subjects are a group of people who have undergone SMILE surgery in the second half of 2020.Clinical examinations were made before operation and 1st and 3rd Month Post-Surgery, respectively, and the results of naked eye vision, diopter, intraocular pressure, slit lamp microscope examination, as well as data of Pentacam (corneal diopter, central corneal thickness, anterior chamber depth) and IOL-Master (corneal power, aqueous depth, axial length) were recorded. In addition, supplementary parameters such as corneal thickness and cutting depth were recorded. We used paired t test to compare the changes of corneal diopter, anterior chamber dimensions and axial measurement measured by Pentacam and IOL-Master before and after SMILE operation. The same method is also used to compare the estimated lens position (ELP) calculated from IOL-Master and Pentacam data according to Holladay I and Haigis formula, and p-value below 0.05 denotes significance. In addition, Pearson correlation coefficient was used to analyze the relationship between the changes of anterior chamber depth measured by IOL-Master and Pentacam before and after SMILE operation and the corneal ablation depth. Results: At postoperative months 1 and 3, the measurement results of ALand（AL*） were notably dissimilar to preoperative measures (P<0.05). Whether measured by IOLMaster or Pentacam equipment, there were significant differences between ICACD and ECCD at 1 month and 3 months after operation (P<0.05). It should be noted that the ICACD value measured by IOLMaster is larger than that measured by Pentacam before and after operation. Similarly, the values of Km, SimK and TCRP were significantly different from those before operation at 1 month and 3 months after operation (P<0.05), and the values of Km were always higher than that of SimK, while that of SimK was higher than that of TCRP before and after operation. When the effective lens position (ELP) was calculated by Holladay I and Haigis formula using the data of IOLMaster or Pentacam, the results of Holladay I(ELP) and Haigis(ELP) were significantly different at 1 and 3 months post-surgery (P < 0.05). In addition, the estimated lens position (ELP) calculated by IOLMaster Haigis data is higher than that measured by Pentacam, and this trend is the same as that of Holladay I (ELP) calculated by IOLMaster before and after operation. Moreover, the ELP value measured by the same examination equipment always shows that the result of Haigis (ELP) after operation is higher than that measured by Holladay I (ELP). Conclusion: 1.After the SMILE operation, we found that the axial length of the eyes became shorter and the anterior chamber depth became shallower. Although the shortening of axial length is related to cutting off a part of corneas, the shallowing of anterior chamber depth has nothing to do with how many corneas are cut off during surgery.2.After SMILE operation, the axial length can be measured accurately with IOL-Master instrument, among which TCRP method is the most reliable, followed by SimK and Km. When measuring anterior chamber depth, Pentacam and IOL-Master are very reliable. 3.He shallowness of anterior chamber depth after SMILE surgery will lead to the doctor's error in estimating the effective lens position, so the calculated intrinsic lens degree will be inaccurate, and finally the vision correction after cataract surgery will be biased.