Changes in effective optical zone after small-incision lenticule extraction in high myopia

Area of Science:

• Ophthalmology
• Corneal Refractive Surgery
• Ophthalmic Imaging

Background:

• Small-incision lenticule extraction (SMILE) is a common refractive surgery for high myopia.
• Accurate determination of the effective optical zone (EOZ) is crucial for optimizing visual outcomes and minimizing aberrations after SMILE.
• Scheimpflug tomography provides detailed corneal measurements essential for EOZ assessment.

Purpose of the Study:

• To compare and evaluate four distinct measurement approaches for determining the effective optical zone (EOZ) after SMILE surgery in eyes with high myopia.
• To assess the consistency and clinical applicability of vertex-based (EOZ_V), pupil-based (EOZ_P), 4 mm-ring-based total corneal refraction (EOZ₄), and tangential curvature difference map (EOZ_D) methods.

Main Methods:

• A retrospective cohort study involving 74 subjects who underwent SMILE for high myopia.
• EOZ was measured 3 months postoperatively using four different methods: EOZ_V, EOZ_P, EOZ₄, and EOZ_D.
• Comparisons were made between the measured EOZs and the planned optical zone (POZ), with analysis of eccentricity, ablation degree, and corneal aberrations.

Main Results:

• All four EOZ measurement methods revealed a reduction in EOZ compared to the POZ (6.48 ± 0.16 mm).
• Measured EOZs were: EOZ_V (5.87 ± 0.44 mm), EOZ_P (5.85 ± 0.45 mm), EOZ₄ (4.78 ± 0.40 mm), and EOZ_D (5.29 ± 0.27 mm).
• Bland-Altman analysis indicated good consistency among the four EOZs, with EOZ_V and EOZ_P showing the smallest difference (0.02 mm).

Conclusions:

• All evaluated methods confirm a reduction in the effective optical zone post-SMILE surgery compared to the planned optical zone.
• The vertex-based (EOZ_V) and pupil-based (EOZ_P) methods demonstrated the closest agreement with the planned optical zone.
• Differences in EOZs did not show significant correlations with eccentricity, ablation degree, or corneal aberrations.