Study population

A total of 67 eligible myopic patients (67 eyes), who were treated at Taiyuan Central Hospital from January 2023 to January 2024 were randomly enrolled in this study and divided into two groups, namely the SMILE group with 32 cases (32 eyes) and the ICL group with 35 cases (35 eyes). The SMILE group included 16 male and 16 female patients, with an average age of 27.5 ± 6.90 years. Likewise, the ICL group had 11 male and 24 female patients, with an average age of 28.6 ± 5.6 years.

Inclusion criteria [19]: (1) provide consent to undergo myopia laser correction surgery with no surgical contraindications; (2) absence of any pre-surgery dry eye symptoms such as foreign body sensation, eye dryness, burning sensation, or vision fluctuation; (3) having normal eyelid structure and morphology with normal appearance and function of the lacrimal puncta, and unobstructed tear ducts; (4) provide consent for the surgical method, postoperative medication plans, and necessary examinations; (5) must be able to attend follow-up appointments at the hospital as scheduled, and (6) should not use of any eye drops within 4 h before the examination.

Exclusion criteria [29]: (1) history of systemic diseases such as cardiovascular and cerebrovascular diseases, diabetes, rheumatoid arthritis, gout, and neuromuscular diseases affecting blinking, like Bell’s palsy and Parkinson’s disease; (2) involvement in long-term outdoor work or prolonged stay in air-conditioned environments; (3) long-term night driving; (4) extensive computer usage; (5) existing moderate to severe dry eye symptoms, and (6) patients who could not maintain the scheduled follow-up visits.

In addition, patients who developed keratoconjunctivitis during the surgery, or those who developed postoperative complications such as inappropriate rotation of the intraocular lens requiring a secondary surgery; and patients who used random medications on their own without following the postoperative medical instructions are also excluded from this study.

This prospective cohort study was approved by the Taiyuan Central Hospital’s Institutional Review Board, strictly conforming to the tenets of the Helsinki Declaration.

Ocular examinationsExamination sequence

All candidates meeting the inclusion criteria were required to fill out an additional Ocular Surface Disease Index (OSDI) questionnaire form before undergoing ophthalmic examinations to record the pre-treatment conditions as a reference. The patient’s demographics, including age, gender, occupation, and history of contact lens wear, were also collected. All participants underwent a comprehensive eye examination for uncorrected visual acuity, best-corrected visual acuity (BCVA), slit-lamp examination, intraocular pressure, indirect ophthalmoscopy, fundus photography, macular OCT examination, corneal topography, and the Oculus Keratograph 5 M assessment. The non-anesthetic Schirmer’s I test (SIT) was the last step in the whole process of clinical examinations. The same procedures were repeated at one week, one month, and three months postoperatively to evaluate the impact of the two surgical methods on dry eye at each time point.

OSDI

OSDI score [30] was developed by the International Dry Eye workgroup and consists of three sections - ocular discomfort, visual function, and environmental triggers. The OSDI score was calculated as follows: (Sum of the scores for each question × 25) / (Number of questions answered). A higher score suggests a more severe impact of dry eye symptoms.

Oculus keratograph 5 M

The Oculus Keratograph 5 M was used for comprehensive analyses of NIBUT, TMH, conjunctival redness, CFS score, lipid layer analysis score, lid margin opening scores, and meibomian gland loss scores. All examinations were conducted independently by the same operator in a dark room. Each subject’s affected eye was examined three times with a ten-minute interval between each examination.

NIBUT

In this process, the subject was instructed to naturally open the eyes and blink twice. Then, the device automatically started to detect the tear film break-up location and time for the concerned eye. The device recorded the patient’s initial tear film break-up time, the average tear film break-up time, and the classification of tear film stability and plotted a distribution map for all selected parameters identifiable by specific colors [31].

TMH

The device’s built-in measurement tool, equipped with a scale feature, was used to measure the tear meniscus height just below the center of the pupil in the affected eye. The same ophthalmologist conducted this measurement three times, and the results were organized from lowest to highest value.

Hyperemic index

Focusing on the corneal surface and covering it with a diffuser plate marker, the subject was instructed to keep their eyes wide open (scanning area ≥ 4 mm²) during the photo session. After capturing the image, the device automatically assessed the degree of conjunctival congestion. This assessment was standardized and quantified, with a scale of 0 indicating minimal congestion, 1 and 2 indicating normal levels, and values above 2 indicating abnormal congestion. Conjunctival congestion, as a clinical indicator of ocular surface inflammation, provides insight into the extent of postoperative ocular surface inflammation and dry eye.

CFS score

The subjects’ conjunctival sacs were instilled with a 1% sodium fluorescein solution (Tianjin Jingming, China) and were instructed to blink several times. The examination interface for corneal fluorescein staining was then accessed, where the image was automatically focused and captured using cobalt blue light. The system’s built-in image processing software counted the number of fluorescein-stained spots on the cornea and assigned a score. The cornea was divided into five regions (superior, inferior, central, nasal, and temporal), with a maximum total score of 12 points [32]. The scoring scale was as follows: 0 points for no staining; 1 point for 5 spots; 2 points for 6–15 spots; 3 points for 16–30 spots. An additional 2 points were given for the presence of corneal filaments, and 1 point for one patch of staining in any region, or 2 points for two or more patches of staining in any region.

Meibomian gland imaging and assessment

Meibomian Gland Loss Scoring: The ocular surface analyzer was first set to infrared photography mode, and then the upper and lower eyelids were flipped to expose the conjunctival surface and adjust the focal length as needed. The images were automatically analyzed and processed by the system. Meibomian gland loss is graded and scored based on its extent: 0 points for no loss; 1 point for loss covering less than 1/3 of the total area; 2 points for loss covering between 1/3 and 2/3 of the total area; and 3 points for loss covering 2/3 or more of the total area [33].

Lipid Layer Analysis: The instrument was focused on the tear film lipid layer while the patient blinked naturally. The lipid layer [34]was then assessed for its color, structure, and granularity, and classified into three grades: Grade 1 for a thin, blurred, and dull-colored lipid layer; Grade 2 for a normal, clear lipid layer with a rich color palette; and Grade 3 for a thick, highly clear lipid layer with very vibrant color. An excessively thin lipid layer indicated an abnormality in meibomian gland function.

Lid Margin Opening Detection Scoring: The patient was instructed to look upward and press the middle third area of the lower eyelid, where there are 8 meibomian glands, using the thumb. The consistency of the secretion from each gland was scored on a 0–24 point scale to semi-quantitatively evaluate the properties of the meibum following this gradation system [35]: 0 points for clear meibum; 1 point for turbid meibum; 2 points for turbid meibum with cloudy particles or debris; and 3 points for thick meibum resembling toothpaste.

Shirmer I test (SIT)

Without surface anesthesia, a tear fluid detection filter strip (5 × 40 mm, Tianjin Jingming, China) was placed in the conjunctival sac of the lower eyelid between the outer and middle thirds. The subjects were then instructed to gently close their eyes for 5 min when the device measured and recorded the length of the tear film area.

Surgical procedures and postoperative treatmentSMILE procedure for refractive lenticule extraction

The SMILE procedure was performed as described previously [4, 36]. Briefly, the 500 kHz femtosecond laser system (Visumax; Carl Zeiss, Germany) was set to 110–120 μm as the intended cap thickness and 7.8 mm as the intended cap diameter. A small tunnel incision (2 mm) was created at a 90˚ angle, and the refractive lenticule was extracted through the incision hole using a spatula. For all myopic corrections, the optical zone size was 6.8 mm. After the surgery, all patients were administered 0.5% gatifloxacin eye drops 4 times/d for 10 days, and 0.1% fluorometholone eye drops tapered every 3 days from 8 times/d to once a day within 3 weeks.

ICL surgical procedure

A 3.0 mm clear corneal incision [37]was made in the upper cornea, and an appropriate amount of sodium hyaluronate (Bausch & Lomb, USA) was injected into the anterior chamber. Using an injector (STAAR Surgical), the ICL V4C intraocular lens was pushed through the 3.0-mm corneal incision. After placing the ICL in the posterior chamber, the surgeon completely removed the viscoelastic agent from the eye using a balanced salt solution, sealed the incision, and covered the eye with a dressing. Surgeries were uneventful and no intraoperative complications were observed afterward. Following surgery, 0.1% Tobramycin dexamethasone (a combination of antibacterial and steroidal medication) was prescribed four times daily for 3 days followed by fluorometholone eyedrops tapered gradually over 2 weeks. Antibiotic eyedrops (0.5% Ofloxacin; Japan) were then prescribed four times daily for 1 week, along with non-steroidal anti-inflammatory eyedrop Pranoprofen four times daily for 2 weeks, and artificial tears four times daily for one month.

Statistical analysis

The Shapiro-Wilk test was used for normality analyses. The mean (standard deviation, SD) and median (quartiles, IQR) were used to describe age, scores, and other measured data. T-test and Mann-Whitney U test were used for intergroup comparisons. The gender was described using the number of cases (percentage; %) and compared between the groups using the chi-square (χ2) test. Repeated measure analysis of variance was used to describe the measured parameters and scores of patients at different time points across the groups. For indicators that did not conform to the sphericity test, Greenhouse-Geisser correction was applied. Indicators without the time-group interaction were described using main effects to show their intergroup differences, while indicators with positive interactions were described using separate effects. Paired t-tests were used to compare differences between the overall population and different groups at different time points. In this study, the significance level α was set at 0.05. All statistical analyses and graph plotting were performed using SPSS 27.0 and R 4.4.1 software packages.