This observational study aims to compare two laser corrective procedures for treating myopia and myopic astigmatism: a novel refractive technique, the CLEAR procedure, and the established SMILE procedure. Participants will be randomized to undergo CLEAR in one eye and SMILE in the other. The investigators will evaluate and compare the two procedures based on the following aspects: refractive predictability (how accurate the vision correction is) by measuring the proportion of eyes close to the target prescription after surgery, clinical dry eye outcomes, changes in tear proteins, and corneal nerve changes at 1, 3, 6, and 12 months after both surgeries. Metabolomic features of the removed corneal tissue and how precisely the laser is centered during surgery will also be examined. Our hypothesis is that CLEAR provides equally good vision results as SMILE, and explore any extra benefits of CLEAR.
>/= 21 years of age and </= 50 years of age.
Cycloplegic spherical equivalent of >-1.00D
Refractive cylinder -2.00 D or less; anisometropia <1.00D
Best spectacle corrected visual acuity (BSCVA) of 6/12 or better in BOTH eyes.
Progressive or unstable myopia and/or astigmatism.
Clinical or corneal topographic evidence of keratoconus.
Patients who want bilateral SMILE procedure
Patients who want extracted corneal lenticule to be stored for future refractive surgery.
A total of 65 subjects (130 eyes- 65 CLEAR eyes and 65 SMILE eyes) will be recruited in the study from refractive clinic at Singapore National Eye Centre.
Cohort
Prospective
Procedure: Corneal lenticule extraction for advanced refractive correction (CLEAR)
Procedure/SurgeryRoutinely conducted procedure using FEMTO LDV Z8 laser system for correction of Myopia.
Procedure: Small Incision Lenticule Extraction (SMILE)
Procedure/SurgeryRoutinely conducted procedure using VisuMax laser system for correction of Myopia.
Rate of refractive predictability
Refractive predictability is defined as the proportion number of eyes achieving a postoperative spherical equivalent (SE) within ±1.0 D of the intended target. Uncorrected visual acuity (UCVA), refraction, and best corrected visual acuity (BCVA) will be recorded.
Level of higher order aberrations
Higher-order aberrations are small optical irregularities of the eye that cannot be corrected with regular spectacles and most contact lenses. HOAs are responsible for an array of visual symptoms such as difficulty seeing at night, glare, halos, blurring, starburst patterns, or double vision.
Tear Break Up Time (TBUT)
TBUT will be measured by determining the time interval between a complete blink and the first appearance of a dry spot on the corneal surface, indicating tear film stability.
Concentration of tear neuromediators assessed by enzyme-linked immunosorbent assay
Tear fluid samples will be collected by the strips from Schirmer's I test. The neuromediators concentration in all tear samples will be analyzed using the enzyme-linked immunosorbent assay
Corneal sensitivity measurements assessed by Cochet-Bonnet esthesiometer
Corneal sensitivity measurements assess the responsiveness of the cornea to external stimuli using a contact esthesiometer (Cochet-Bonnet), evaluating the functional status of corneal nerves.
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