Astigmatism, Myopia
Conditions
Keywords
Refractive Surgical Procedures, small-incision lenticule extraction, lenticule extraction, inflammatory mediators
Brief summary
The aim is to evaluate the short-term changes in ocular surface measures and tear inflammatory mediators after lenticule extraction (FLEx) and small-incision lenticule extraction (SMILE) procedures.
Detailed description
The use of femtosecond (FS) laser has become one of the most significant technological advancements in refractive surgery. A breakthrough FS laser-assisted myopic and myopic astigmatic correction procedure can now be performed using a prototype femtosecond system. This first all-in-one FS-laser system was designed to perform the refractive lenticule extraction (ReLEx) procedures, femtosecond lenticule extraction (FLEx) and small-incision lenticule extraction (SMILE). In FLEx, a corneal flap is created by the FS laser (similar to LASIK) and lifted, allowing lenticule removal. For SMILE, a truly without flap procedure, only a small-2-4mm- incision is made, through which the lenticule is removed. Ocular surface disruption during corneal refractive surgery is commonly considered to be closely related to the development of dry eye. Multiple etiologies contribute to this ocular surface disruption, including the flap creation and stromal ablation involved in previous refractive surgery techniques. Corneal nerve damage has been considered the main cause of dry eye, due to disrupted afferent sensory nerves, reduced blink reflex, and increased tear evaporation leading to tear film instability. In addition, postoperative inflammatory mediator fluctuations are also a key factor related to ocular surface damage. Extensive research has described the effects of cytokines, chemokines and growth factors in modulating corneal wound healing, cell migration, and apoptosis on the ocular surface after refractive surgery. For both FLEx and SMILE, stromal ablation has been replaced by refractive lenticule removal. In terms of corneal flap formation, FLEx still requires an epithelial-stromal flap, while SMILE employs only a small incision to extract the lenticule. Hence, the investigators hypothesize that SMILE will have less effect on patients' ocular surface markers and inflammatory mediators, compared to FLEx. In support of this hypothesis, previous studies have reported that more damage to the sub-basal nerve plexus of the cornea and more changes in ocular surface evaluations were found after FLEx than after SMILE. In this study, the investigators have focused on postoperative changes to tear inflammatory mediators and the relationship of FLEx and SMILE to dry eye.
Interventions
PROCEDURElenticule extraction
Four femtosecond incisions were created in succession: the posterior surface of the refractive lenticule (spiral in), the lenticule border, the anterior surface of the refractive lenticule (spiral out), and the corneal flap in the superior region. After the suction was released, the flap was opened using a thin, blunt spatula and the free refractive lenticule was subsequently grasped with a forceps and extracted, after which the flap was repositioned carefully
PROCEDUREsmall-incision lenticule extraction
Four femtosecond incisions were created in succession: the posterior surface of the refractive lenticule (spiral in), the lenticule border, the anterior surface of the refractive lenticule (spiral out), make a small incision
Sponsors
Sun Yat-sen University
Study design
Allocation
NON_RANDOMIZED
Intervention model
PARALLEL
Primary purpose
TREATMENT
Masking
NONE
Eligibility
Sex/Gender
ALL
Age
18 Years to 25 Years
Healthy volunteers
Yes
Inclusion criteria
* minimum age of 18 years(range from 18 year to 25 years); corneal thickness 500 μm with calculated residual stromal bed after treatment greater than 300 μm; preoperative spherical equivalent refraction between * 2.00 diopter (D) and -6.50 D; preoperative cylindrical equivalent refraction between -0.25 D and -1.50 D; preoperative corneal curvature from 41.0 D to 46.0 D with a regular topographic pattern, verified with an Atlas topographer; monocular best corrected visual acuity of 20/20 or better and stable refractive error (less than 0.5 D change) for 24 months before surgery
Exclusion criteria
* systemic disease that contraindicated the surgery (such as diabetes, glaucoma and systemic collagen vascular disease); corneal abnormality or disease; a history of tear supplement usage or contact lens wear during the past year
Design outcomes
Primary
| Measure | Time frame |
|---|---|
| concentration of matrix metalloproteinase-9 | up to 1month after surgery |
| questionnaire of ocular surface disease index | up to 1month after surgery |
| scale of central corneal sensitivity | up to 1month after surgery |
| scale of tear meniscus height | up to 1month after surgery |
| scale of Schirmer I test | up to 1month after surgery |
| scale of corneal fluorescein staining | up to 1month after surgery |
| scale of noninvasive tear breakup time | up to 1month after surgery |
| concentration of Interleukin-1α | up to 1month after surgery |
| concentration of tumor necrosis factor-α | up to 1month after surgery |
| concentration of nerve growth factor | up to 1month after surgery |
| concentration of interferon-γ | up to 1month after surgery |
| concentration of transforming growth factor-β1 | up to 1month after surgery |
Secondary
| Measure | Time frame |
|---|---|
| Correlation Between Inflammatory Mediators and Ocular Surface Changes | up to 1month after surgery |
Outcome results
None listed