Research Progress on Morphological Changes and Surgery-Related Parameters of Corneal Cap in Small-Incision Lenticule Extraction

Abstract

Small-incision lenticule extraction (SMILE) is an “all-in-one” surgical method for refractive correction. An advantage of the SMILE over traditional surgery is that it depends on the corneal cap’s design. This review discusses the morphological evaluation of the corneal cap, selection of the corneal cap with different thicknesses and diameters, influence of the corneal cap design on re-treatment, and management of corneal cap-related complications. The following points should be recognized to define the correct morphology and design of the operation-related parameters of the corneal cap during SMILE: (1) the thickness and diameter of the corneal cap are predictable and influence postoperative visual quality, (2) the change in the anterior surface curvature of the corneal cap should be considered in the design of the nomogram value, (3) for patients with moderate myopic correction, early visual quality is better with a 6.9-mm than with a 7.5-mm-diameter corneal cap, (4) there is no significant difference in visual quality or biomechanics among corneal caps with different thicknesses, (5) the primary corneal cap thickness plays an important role in the SMILE re-treatment, (6) a 7.78-mm diameter corneal cap has a greater risk of suction loss than a 7.60-mm diameter corneal cap, (7) if suction loss occurs when lenticular scanning exceeds 10%, then SMILE can be continued by changing the corneal cap thickness, (8) preventive collagen cross-linking with SMILE caps are 90–120 μm thick and 7–7.8 mm in diameter, and (9) properly treating SMILE-related complications ensures better postoperative results. The data presented herein shall deepen the understanding of the importance of the corneal cap during SMILE and provide diversified analysis for personalized operational design of corneal cap parameters.