Study of the MEL 80 Excimer Laser Using LASIK in the Treatment of Mixed Astigmatism

LASIK has become one of the most common refractive eye procedures performed in the country. In the mixed astigmatism procedure, a combination of both a steepening (hyperopic treatment) and a flattening (myopic treatment) occur on the corneal surface. The surgeon will produce a standard keratomileusis flap using a microkeratome, exposing the corneal stroma. Recontouring under the flap is then accomplished by the removal of tissue from the stroma with the laser. This recontouring results in an altering of effective lens power of the central cornea, measured in diopters (D). The MEL 80 Excimer Laser System will be evaluated for its ability to create accurate and stable mixed astigmatic refractive correction results.

Inclusion criteria

• Naturally occurring mixed astigmatism when the magnitude of cylinder (up to 6.0 D) is greater than the magnitude of sphere, and the cylinder and sphere have opposite signs, at the spectacle plane;
• Have a stable refraction for at least the past twelve months, as demonstrated by a change of less than or equal to 0.50 D preoperative spherical equivalent shift over twelve months prior to surgery;
• Discontinue use of contact lenses at least 2 weeks for hard contacts and 3 days for soft lenses prior to the preoperative examination;
• Hard contact lens wearers must have two central keratometry readings and two manifest refractions taken at least one week apart that do not differ by more than 0.50 D
• Have visual acuity correctable to at least 20/40 in both eyes
• Have no more than 0.75 D of latent hyperopia as determined by the difference between the preoperative manifest refractive spherical equivalent (MRSE) and cycloplegic refractive spherical equivalent (CRSE);
• Be at least 18 years of age
• Corneal topography should be normal;
• The operative eye must be targeted for emmetropia;
• Be willing and able to return for scheduled follow-up examinations for twelve months after surgery;
• and provide written informed consent.

Exclusion criteria

• History of anterior segment pathology, including cataracts (in the operative eye);
• Clinically significant dry eye syndrome unresolved by treatment;
• Residual, recurrent, active ocular or uncontrolled eyelid disease, corneal scars within the ablation zone or other corneal abnormality such as recurrent corneal erosion or severe basement membrane disease;
• Ophthalmoscopic signs of keratoconus (or keratoconus suspect);
• Required ablation is deeper than 250 microns from the corneal endothelium;
• Irregular or unstable (distorted/not clear) corneal mires on central keratometry readings;
• Blind in the fellow eye;
• Previous intraocular or corneal surgery of any kind in the operative eye(s), including any type of surgery for either refractive or therapeutic purposes;
• History of ocular Herpes zoster or Herpes simplex keratitis;
• History of steroid-responsive rise in intraocular pressure, glaucoma, or preoperative IOP >21 mm Hg;
• Diabetes, diagnosed autoimmune disease, connective tissue disease or clinically significant atopic syndrome;
• Immunocompromised patients, or use of chronic systemic corticosteroid or other immunosuppressive therapy;
• Pregnant, lactating, or child-bearing potential and not practicing a medically approved method of birth control;
• Sensitivity to planned study medications;
• Simultaneous participation in other ophthalmic drug or device clinical trial.
• For Fellow (Second) Eyes in Simultaneous Bilateral Treatment Procedures
• 1. Flap complications during the first eye's surgery such as a free cap, partial flap, thin flap, or irregular flap.
• 2. Epithelial defect exceeding 2 mm x 2 mm in dimension, or clinically significant debris in the interface between the flap and underlying stroma for the first eye.
• 3. Severe blepharospasm in the first eye that may have prevented or impeded the completion of the keratectomy and/or the laser ablation procedure.
• 4. Poor subject cooperation with instructions for the first eye's surgery and/or poor subject fixation on the laser fixation target.
• 5. Aborted LASIK procedure in the first eye or PRK was performed in the first eye because LASIK was not possible.