Corneal Refractive Surgery

Corneal Refractive Surgery

Corneal Refractive Surgery is a specific type of ophthalmologic surgical procedures aimed at correcting or improving the refractive state of the patient’s eye in order to eliminate or reduce the defects causing vision disorders, and as such reducing or eliminating the dependency on contact lenses and glasses. Corneal Refractive Surgery operations include various procedures through which the patient’s cornea is remodeled, as well as cataract surgical operations. Vision disorders such as hyperopia, myopia and astigmatism have been corrected or at least reduced through the modern methods and procedures of refractive eye surgery.

Myopia, or in more common terms “short-sightedness”, is a vision disorder caused by a refractive defect of the patient’s eye. More specifically, when accommodation is relaxed, the collimated light produces a focus of the image in front of the retina.

Hyperopia, otherwise commonly known as hypermetropia, is another vision defect caused by a refractive defect of the patient’s eye. A patient affected by hypermetropia is unable or encounters difficulties when trying to focus on objects that are close. In severe situations, the patient has a hard time trying to focus on objects located at any distance. This is caused by insufficient power of the retina to focus the image or to keep it focused, in the case of moving objects. The most common symptoms of hypermetropia are asthenopia, blurred vision, ambylopia, strabismus, accommodative and binocular dysfunctions.

Astigmatism is an ophthalmologic disorder which causes constant blurred vision, as the patient’s eye is unable to focus an object on the retina; one of the main causes for this disorder is a toric or irregular corneal curvature.

All the above ophthalmologic conditions are typically corrected by using glasses or contact lenses; however, due to the new techniques available through Corneal Refractive Surgery, these vision problems and others may be permanently corrected so that the patient will never need glasses or contact lenses again.

Corneal Refractive Surgery Description

Corneal Refractive Surgery includes a number of various ophthalmologic surgical techniques. We will try to familiarize you with them in this chapter.

Flap procedures are surgical operations during which the ablation with the excimer laser is performed under a corneal lamellar flap of partial thickness. These procedures include automated lamellar keratoplasty (ALK) and laser assisted in-situ keratomileusis (LASIK).

Surface Corneal Refractive Surgery procedures are defined by the use of an excimer laser to ablate most of the corneal stroma anterior portion; the only difference between the procedures is the method of handling the epithelial layer. Examples of such procedures are photorefractive keratectomy (PRK), laser assisted sub-epithelium keratomileusis (LASEK) and EPI-LASIK.

Corneal incision procedures include radial keratotomy (RK) and arcuate keratotomy (AK), two similar procedures which have been largely replaced by the above methods. These procedures employ the use of a diamond knife to perform the incisions on the cornea before performing the necessary alterations. Other Corneal Refractive Surgery procedures include thermal keratoplasty, laser thermal keratoplasty (LTK), conductive keratoplasty (CK), intrastromal corneal ring segments and lens implantation.

Corneal Refractive Surgery also has a number of contraindications. For example, such procedures may not be performed safely on patients that are suffering from diabetes, from autoimmune disease or uncontrolled vascular disease, patients with glaucoma or eye disorders that involve the retina or cornea. Also, such procedures should not be performed during pregnancy. Patients suffering from keratoconus may not undergo this type of ophthalmic surgery as it may worsen their condition, situation which may require corneal transplant. In addition, the eye structure may not permit such operations in the case of some individuals. Prior to undergoing refractive surgery, all patients are required to have a full eye examination, and modern examination techniques such as corneal topography, Pentacam or pachymetry are used to detect corneal abnormalities in candidates for laser ophthalmic surgery.

Serious risk may be associated with refractive surgical procedures. Although the chances are low, it is possible for patients to develop vision disorders such as starbursts, ghosting, double vision, halos or dry eye syndrome; also, procedures which involve creating permanent flaps may lead to the traumatic displacement of the flaps with grave results.

Corneal Refractive Surgery Related Medication

In the past, anesthetic agents were administered through an injection; currently, topical agents are preferred due to the lower risk factor. Most of the Corneal Refractive Surgery procedures involve application of topical anesthesia prior to the operation. The most common topical anesthetic agents used are Propacaine, Cocaine, Tetracaine, Lidocaine or Bupivacaine. Propacaine 0.5% takes effect rapidly, within 1 minute from application, as well as Tetracaine 0.5%, and the effect lasts for 15 minutes for both. However, Propacaine may be recommended due to the fact that Tetracaine is more toxic to the surface of the eye.

Cocaine may be used in concentrations of 0.5% or 2% and it also takes effect fast; however, its effect lasts for a shorter period of time. Also, studies have shown that Cocaine usage may cause complications due to the fact that it may loosen the epithelium of the cornea causing recurrent erosion, or in some cases intraoperative corneal abrasion. It also has a vasoconstrictor effect and may cause a dilation of the pupil; as such, it is of limited use during Corneal Refractive Surgery.

Bupivacaine 0.75% is a potent amide anesthetic agent but its effect takes longer to set in. As such, it is not commonly used as a topical anesthetic – instead it is very common as an injectable agent.

Lidocaine is another anesthetic agent with remarkable properties, including rapid penetration and diffusion. It has a strong, long-lasting effect regardless of the administration method – topical, injection or even intraocular administrations have yielded great results. The formulation employed for intraocular administration is the same preservative-free formulation commonly employed by specialists in other areas of expertise such as cardiologists.

Apart from anesthetic agents, the supervising health care professional may direct the use of other pharmaceutical substances which have not been presented in this guide. If you would like to obtain additional information regarding the Corneal Refractive Surgery procedures available or if you are interested to learn more about the medication that may be used prior, during or after these operations, it is recommended that you consult with a specialized surgeon or an ophthalmologist.