A Quantitative Measurement of Ocular Rotation in Small Incision Lenticule Extraction: Double Marking of Corneal Limbus and Sclera

Summary

Here, we present a protocol for quantitatively measuring intraoperative ocular rotation using a corneal-scleral double-marking technique. This method assists researchers in measuring the effect of ocular rotation during refractive surgery and provides specific, scientific operational approaches for the implementation of clinical research.

Abstract

The small incision lenticule extraction (SMILE) has become a mainstream surgical procedure for correcting myopia and astigmatism. Nevertheless, the lack of an active cyclotorsion-tracking system prevents it from correcting rotational errors, which may compromise astigmatic correction accuracy. Evidence regarding the influence of intraoperative cyclotorsion on SMILE outcomes remains scarce, largely because of the unavailability of viable and dependable methods of measuring the degree of rotation during an operation. To address this gap, this protocol describes a novel corneoscleral double-marking technique to overcome a fundamental methodological limitation. It involves creating positional and dye-based marks on both the corneal and scleral surfaces, enabling direct observation and quantitative measurement of ocular rotation under a surgical microscope or a slit lamp. The primary goal of this protocol is to establish a standardized, objective approach for obtaining precise, quantitative data on cyclotorsion that has previously been inaccessible. The representative results of the statistical analysis of this data indicate that ocular rotation amplitude is an independent risk factor for residual astigmatism after SMILE surgery and has a significant impact on it (β = 0.520, P < 0.001). The analysis of astigmatism vectors also confirmed this. Therefore, the availability of this quantifiable data is pivotal. It provides an essential research tool to systematically investigate the specific impact of cyclotorsion in SMILE surgery. The measurements obtained are crucial for advancing studies on postoperative astigmatic outcomes, developing accurate predictive models for surgical accuracy, and refining treatment nomograms.

Introduction

The small incision lenticule extraction (SMILE) is an advanced type of corneal refractive surgery, and has a number of benefits over conventional laser in situ keratomileusis (LASIK)^1,2,3,4. Now, SMILE has become mainstream practice in the correction of myopia and astigmatism^5,6. Nevertheless, the SMILE surgery is prone to causing under-correction and regression in the correction of patients with moderate to high myopia and astigmatism^7,

Protocol

All the ocular samples used in this study were collected from the Ophthalmology Department of the Second Affiliated Hospital of Guizhou Medical University. They were approved by the Ethics Committee of the Second Affiliated Hospital of Guizhou Medical University (Approval Number: 2022-lunshen-127), which complies with the Helsinki Declaration. All the subjects signed the informed consent form before the surgery. Please proceed as follows.

1. Preoperative preparation

1. Routinely irrigate the conjunctival sac of the surgical eye with 0.9% sodium chloride solution, disinfect the ocular surface with 5% povidone-iodine....

Results

This study measured the effective rotation amplitude during SMILE procedures using a dual-marking technique on both the sclera and cornea. What we have collected is the ocular rotation amplitude of the Chinese population. Figures 1A,B illustrate the schematic diagrams of the eyeball positions in the supine (during surgery) and sitting (immediately after surgery) positions, clearly contrasting the ocular rotation caused by the changes in body position. Fi.......

Discussion

Current studies blame astigmatism correction divergences during SMILE surgery on various factors, including ocular rotation, a vital yet poorly measured clinical factor^12,13. The artificial intelligence approach to measuring rotation that is based on the division of the optic disc and fovea in fundus images is hard to apply to the SMILE surgical environment^16,17. Even though S.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Disposable sterilized syringe	Shandong Weigao Group Medical Polymer Products Co., Ltd.	CNDA Registration Number: 20163141593	Mark
Femtosecond laser treatment machine	Visumax, Carl Zeiss Meditec AG	100799115	Treatment
Marking ruler	Dongguan Tangde Medical Technology Co., Ltd.	Guangdong Medical Device Registration Number20202021011	Auxiliary marking
Medical marking pen	Dongguan Tangde Medical Technology Co., Ltd.	Guangdong Medical Device Registration Number20202021011	Mark
Slit-lamp microscope	Topcon Corporation	ZCKP020191110100041	Observation and Measurement