Manually Performed Limbal Relaxing Incisions vs Femtosecond Laser-guided Astigmatic Keratotomy
Condition: Corneal Astigmatism
MeSH terms: Astigmatism
Study type: Interventional

Summary: 
      Astigmatic keratotomy (AK) is used to treat numerous refractive disorders, including
      congenital astigmatism, residual corneal astigmatism at the time of or following cataract
      surgery, post-traumatic astigmatism, and astigmatism after corneal transplantation.

      Within the past few years, much consideration has been given to an evolutionary variant of
      the procedure, the limbal relaxing incision (LRI). By moving the incision farther to the
      periphery, cataract surgeons can safely and predictably remediate mild to moderate amounts of
      regular astigmatism at the time of cataract surgery by performing this incisional technique.

      Recent technological developments have shifted ophthalmologist's attention from manually
      created LRIs and astigmatic keratotomy procedures to femtosecond laser-guided procedures.
      Femtosecond lasers offer superior incisional accuracy and reproducibility coupled with
      minimal effects on collateral tissues, achieving levels of safety and reproducibility
      exceeding those of mechanical techniques. A major clinical application of the femtosecond
      laser is for creating arcuate incisions that have a precise and accurate length, depth,
      angular position, and optical zone.
    

Detailed description: 
      Pre-operative evaluation:

        1. Close examination of the peripheral cornea by slit lamb, particularly in the areas where
           the incisions will be placed.

        2. Fundus examination to exclude other causes of diminution of vision.

        3. IOP measure.

        4. Precise manifest refraction, uncorrected visual acuity and best corrected visual acuity
           by snellen's chart.

        5. Standard keratometry to confirm diopters of corneal astigmatism.

        6. Corneal Tomography (Pentacam).

      Surgical procedures:

      LRIs are performed using topical anesthesia. Patients are instructed to fixate on the
      microscope light. Before surgery, the steep meridian was identified with a marker dyed with
      methylene blue with the patient sitting up right. A diamond knife is set at a depth of 0.600
      mm to 0.650 mm based on the peripheral pachymetric readings over the area of intended
      incision. The goal was a maximum reduction in astigmatism without overcorrection in with-the
      rule cases and with little overcorrection in against the rule cases. In the case of an
      overcorrection, the LRI can be sutured without creating any irregular astigmatism.

      Performing femtosecond laser-guided astigmatic keratotomy requires the parameters of length,
      position, depth and distance from the visual axis where the incisions will be created. The
      depth of our incisions is 85% of the corneal pachymetry in the area of the incision. We have
      set our distance from the visual axis at 8 mm. This information is all downloaded onto the
      femtosecond laser. Then, we begin the surgical procedure by docking the laser onto the
      cornea. An overlay of the incisions is then visible on the surgical screen. After treatment,
      we bring the patient to the operating microscope and open the incisions with a Sinskey hook.
      By using low energy, the incisions do not have significant effect until they are opened.
    

Intervention name(s): limbal relaxing incisions; astigmatic keratotomy
Intervention type(s): Procedure; Procedure
Intervention description(s): Manually performed surgical procedure; femtosecond laser guided surgical procedure
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment