Institutional Ethics committee approval will be obtained and trial registered with Clinical Trial Registry of India. Patients informed consent will be taken and the procedure explained to them in their own language.

Study design: prospective, randomized, hospital-based, single center interventional clinical study in patients with planned keratorefractive surgery.

Study Population: all patients attending the refractive OPD between 21-40 yrs of age.

Study Setting: Nethradhama Superspeciality Eye Hospital, Bangalore.

Sample size: 50 patients undergoing bilateral keratorefractive surgery.

Patient selection criteria: Selection of refractive surgical procedure will be decided as per the following criteria: Patients will be enrolled into the clinical study and randomized as per the discretion of the Investigator. The patients will also be willing to attend routine follow-up care as described below (1 day up to 6 months post-surgery).

Study Duration: Time frame for patient visits and examination are pre-operative, day of surgery, postoperative days 1, 14, and 90

Inclusion criteria:

Patients with simple myopia and myopic astigmatism

Manifest spherical equivalent -10 D or less

Manifest cylinder 3 D or less

SE difference of 2 D or less between 2 eyes

Stable refraction (less than 0.50 D change in past 1 year)

Best spectacle-corrected visual acuity (BSCVA) of 6/6 or better in both eyes

No evidence of irregular astigmatism on corneal topography in both eyes

Residual stromal bed thickness (RSBT) – 280 micrometer or more

Exclusion criteria:

·       Kerato-ectatic conditions such as keratoconus, keratoconus suspects, pellucid marginal degeneration etc.

·       Patients having hypermetropia, mixed astigmatism with presbyopia.

·       Patients who have undergone any refractive procedure previously.

·       Anisometropia of 2D or more

·       Amblyopia

·       Progressive or unstable myopia and /or astigmatism

·       History of ocular surgery, severe dry eye, corneal degeneration, corneal dystrophy, cataract, uveitis, retinal pathology

·       Concurrent use of medication likely to affect interface healing

·       Immunocompromised state/pregnancy/nursing mothers/cancer patients

Equipments used:

1.     Ziemer FEMTO LDV Z8 platform for refractive correction (CLEAR)

2.     ETDRS charts at 4 m for distance visual acuity assessment

3.     Pentacam (Oculus Optikgeraete GmbH) for keratometry and pachymetry

4.     MS-39 (CSO, Italia) for combined tomography, epithelial thickness profile, and non-invasive tear film break-up time (NIBUT).

5.     Corvis-ST (Oculus Optikgeräte GmbH) for corneal biomechanical indices like Corvis biomechanical index (CBI) and Tomographic Biomechanical Index (TBI).

6.     HD Analyzer (Keeler Visiometrics, USA) for objective scatter index (OSI).

7.     iTrace (Tracey Technologies) for higher order aberrations and angle kappa.

Before the surgery, all patients will undergo a complete ophthalmic examination including manifest refraction, slit lamp biomicroscopy, noncontact tonometry (Topcon CT-80), and dilated fundus examination. All eyes will be targeted for emmetropia.

Surgical technique:

The study participants will undergo keratorefractive lenticule extraction (KLEx) using the Ziemer Ophthalmic Systems.  

The CLEAR procedure employs the Zeimer Z8 femtosecond laser to create a refractive lenticule within the corneal stroma using a low-energy, high-frequency flying spot laser. Limbal markings are initially done at 0 and 180°. Under topical anesthesia, the laser creates two intrastromal planes, separated by a thickness corresponding to the refractive correction, along with a peripheral incision of approximately 2–4 mm for lenticule access. The laser uses low energy – below 50 nJ. The lenticule is then carefully dissected and removed through the incision using surgical instruments. The parameters in all cases will be as follows: cap thickness: 120 microns, energy cut index: between 20-25, incision: 2mm superiorly.

Method of data collection:

Data will be collected on the demographic profile (age, gender, address, and occupation) and ocular parameters of the patients, as measured by slit lamp examination, 90D lens with slit lamp, and indirect ophthalmoscopy.

The following tests will be performed pre-operatively:

1.     Detailed slit lamp and dilated fundus examination

2.     Uncorrected Distance Visual Acuity (UDVA)

3.     Corrected Distance Visual Acuity (CDVA)

4.     Manifest refraction

5.     Corneal tomography with Pentacam (Oculus Optikgeraete GmbH)

6.     MS-39 (CSO, Italia) for combined tomography, epithelial thickness profile, and non-invasive tear film break-up time (NIBUT).

7.     Corvis-ST (Oculus Optikgeräte GmbH) for corneal biomechanical indices like Corvis biomechanical index (CBI) and Tomographic Biomechanical Index (TBI).

8.     HD Analyzer (Keeler Visiometrics, USA) for objective scatter index (OSI).

9.     iTrace (Tracey Technologies) for higher order aberrations and angle kappa

Post-operatively on day 1, 2 weeks, 3 months the following tests will be conducted.

a.         Slit lamp examination for corneal state and interface clarity

b.         Uncorrected Distance Visual Acuity (UDVA)

c.         Corrected Distance Visual Acuity (CDVA)

d.         Manifest Spherical Equivalent refraction (SE)

e.     Corneal tomography with Pentacam (Oculus Optikgeraete GmbH)

f.      MS-39 (CSO, Italia) for combined tomography, epithelial thickness profile, and non-invasive tear film break-up time (NIBUT).

g.     Corvis-ST (Oculus Optikgeräte GmbH) for corneal biomechanical indices like Corvis biomechanical index (CBI) and Tomographic Biomechanical Index (TBI).

h.     HD Analyzer (Keeler Visiometrics, USA) for objective scatter index (OSI).

i.      iTrace (Tracey Technologies) for higher order aberrations and angle kappa

Any side effects or complications occurring will be documented and duly reported to the ethics committee.