Comparison of Myopic Small Incision Lenticule Extraction (SMILE) With VISUMAX 500 Versus VISUMAX 800 Platforms

The in-house patient questionnaire is used to assess patient-reported subjective intraoperative experiences. Rather than utilizing numerical scoring, it uses qualitative descriptors and binary "Yes/No" responses to evaluate perceived discomfort, fear levels, and visual phenomena-such as light perception loss or image clarity-during specific surgical steps like vacuum suction and lenticule creation. The form also includes a ranking system for identifying the most fearful parts of the procedure and asks patients to compare the experience, including perceived speed, between their right and left eyes.

The in-house questionnaire is used to assess patient-reported outcomes. This evaluates postoperative outcomes for SMILE surgery performed on the VisuMax 500 and 800 platforms. Rather than using simple numerical scores, the assessment captures subjective patient experiences through qualitative descriptors and frequency-based scales for symptoms like light sensitivity, dryness, and visual disturbances. It also identifies specific environmental triggers, such as lighting conditions, and monitors the functional impact of surgery on daily activities like night driving.

The Surgeon Questionnaire evaluates the intraoperative technical performance and early postoperative outcomes of SMILE procedures. Rather than relying on a single numerical score, it utilizes a combination of binary "Yes/No" indicators for surgical complications and descriptive scales to grade tissue adherence and ease of lenticule extraction.

The Ocular Surface Disease Index (OSDI) is a 12-item questionnaire used to assess the symptoms of ocular irritation. The score ranges from 0 to 100. Higher scores indicate more severe ocular surface disease and a worse outcome.

The Ocular Pain Assessment Survey (OPAS) is a questionnaire used to evaluate ocular pain and its impact on daily functioning and quality of life. The score ranges from 0 to10, where 0 indicates no pain or interference and 10 indicates the most severe pain or maximum interference.

The Corvis ST (Corneal Visualization Scheimpflug Technology) is a non-contact device that measures corneal biomechanical properties by recording corneal deformation in response to an air puff. The higher deformation amplitude (mm) indicating softer cornea and lower corneal stiffness.

The Brillouin Optical Scanning System (BOSS) is a non-contact device that maps corneal and ocular tissue biomechanics using Brillouin light scattering. It measures Brillouin frequency shifts at multiple points, which are converted to stiffness values (GPa). Higher Brillouin shifts indicate stiffer tissue, while lower shifts indicate softer tissue, allowing quantitative assessment of corneal biomechanical properties.

The Schirmer test is a clinical measure of tear production. A standardized filter paper strip is placed in the lower conjunctival fornix for 5 minutes, and the length of wetting (mm) is recorded. Lower values indicate reduced tear secretion, with ≤5 mm typically suggesting severe aqueous tear deficiency, 6-10 mm moderate, and >10 mm normal tear production.

Tear Break-Up Time (TBUT) measures tear film stability by timing the interval between a blink and the first appearance of a dry spot on the cornea after fluorescein instillation. It is recorded in seconds, with shorter times indicating less stable tear film. Values <10 s are generally considered abnormal, while longer times indicate normal tear stability.

Corneal sensitivity is measured using a Cochet-Bonnet esthesiometer, which applies a 0-6 cm nylon filament to different corneal locations. The filament length at which an escape response, blink reflex, or subject-reported sensation occurred is recorded. Summing the responses across all tested locations yielded a total corneal sensitivity score ranging from 0 to 30 cm, with higher values indicating greater corneal sensitivity.

The National Eye Institute (NEI) scale is used to grade the severity of ocular surface staining. The cornea is divided into 5 sectors (central, superior, inferior, nasal, and temporal), and the conjunctiva is divided into 6 sectors. Each sector is scored from 0 to 3 based on the density of staining. The total corneal score ranges from 0 to 15, and the total conjunctival score ranges from 0 to 18 (total maximum score of 33). A score of 0 represents no staining (best outcome), and a higher total score indicates more severe ocular surface damage (worst outcome).

The Oxford Grading Scale is a validated method used to quantify the severity of epithelial damage via fluorescein staining. Staining is assessed in three zones: the nasal conjunctiva, the cornea, and the temporal conjunctiva. Each zone is graded from 0 to 5 based on the density of punctate staining. The total score ranges from 0 to 15, where a score of 0 indicates no staining (best outcome) and a score of 15 indicates confluent staining (worst outcome). Higher scores represent increased ocular surface disease severity.

Corneal tomography is a non-invasive imaging technique that generates a comprehensive 3D map of the cornea's front and back surfaces. The measurements include corneal thickness (μm) and surface curvature (D).

Anterior Segment Optical Coherence Tomography (ASOCT) is a non-invasive imaging technique that produces high-resolution, cross-sectional views of the front portion of the eye. It provides precise structural measurements, including corneal thickness (µm) and anterior chamber dimensions or curvature (mm). These detailed values allow for the clear visualization of ocular anatomy and the monitoring of subtle changes in tissue structure over time.

Higher-order aberrations (HOAs) are complex optical imperfections, such as coma and spherical aberration, that cannot be corrected by standard spectacles or contact lenses. These irregularities are measured using wavefront sensing technology, which quantifies the deviation of light as it passes through the eye's optical media. The primary numerical result is the Root Mean Square (RMS) error, expressed in microns (μm), which represents the total magnitude of these distortions. In a typical healthy eye, the HOA RMS is generally less than 0.30 μm, while values exceeding 0.50 μm often indicate clinically significant visual disturbances like halos or glare.

In Vivo Confocal Microscopy (IVCM) is a non-invasive imaging technique that provides high-resolution, real-time "optical sections" of the living cornea at a cellular level. Rather than traditional photography, it produces detailed scans of individual corneal layers, allowing for the precise measurement of cell density in cells/mm² and nerve fiber morphology in µm/mm². Particularly this is used to assess the nerve and keratocyte changes after surgery.

Intraoperative centration of the laser is measured by the offset distance (in millimeters) between the intended treatment center and the actual center of the laser-cut lenticule. During docking, the surgeon aligns the suction cone with a specific reference point, such as the corneal vertex or pupil center, while the patient fixes their gaze. An offset of less than 0.2 mm indicates ideal centration, whereas a displacement above 0.5 mm is generally considered clinically significant and may cause visual disturbances.

Incidence of surgical and clinical complications related to the SMILE procedure is recorded. Intraoperative complications include suction loss, opaque bubble layer formation, or difficult lenticule extraction. Postoperative complications include epithelial ingrowth, diffuse lamellar keratitis, infectious keratitis, or transient light sensitivity syndrome. Complications will be recorded based on clinical examination and slit-lamp microscopy. Results will be reported as the number of eyes experiencing one or more adverse events.