Introduction
The cornea is the transparent outermost layer of the eye that helps to focus light and acts as a barrier against dust and germs. Light rays that enter the eye are focused by the cornea and the lens onto the retina, which sends signals to the brain to perceive the image. Individuals with refractive problems have difficulty focusing the image correctly on the retina, resulting in blurred vision. Common conditions that affect the eyes or cornea include nearsightedness, farsightedness, allergies, inflammation, dry eyes, or injury. Rarely, conditions such as corneal dystrophy may compromise corneal health. Recently, huge advances have taken place in the field of ophthalmology. Many corneal conditions can be treated with medications and lifestyle management. However, some severe cases require surgical intervention. These surgeries reshape the cornea, correct the vision, and improve the patient's quality of life.
What Is Corneal Refractive Surgery?
Vision correction surgery or corneal refractive surgery is a surgical procedure performed to treat corneal problems or refractive errors of the eye. Multiple options are available these days for the individualized correction of refractive errors. Refractive surgery mainly involves reshaping the cornea to correct errors such as myopia (nearsightedness), hyperopia (far-sightedness), astigmatism (irregularly shaped cornea), presbyopia (gradual loss of the ability to see things close by), etc. Surgical intervention helps the patients focus the light correctly on the retina, thus improving their vision. Some of the common refractive surgeries include laser-assisted in situ keratomileusis (LASIK), small incision lenticule extraction (SMILE), and photorefractive keratectomy (PRK). The type of refractive surgery depends on the refractive error; it corrects the problems and decreases the individual’s need for glasses or contact lenses.
How Is Corneal Refractive Surgery Performed?
Corneal refractive surgeries have been performed for over 20 years, and recent advances have resulted in minimally invasive and more effective techniques. Corneal refractive surgeries are usually safe, effective, and cost-effective, fulfilling the predictability of the refractive outcome. It mainly reduces the need or dependency on glasses or contact lenses. It is recommended after a detailed eye examination for patients above 18 years and with stable refraction (glass power). The most commonly recognized type of corneal refractive surgery is laser-assisted in situ keratomileusis. Alternatives to LASIK (laser-assisted in situ keratomileuses) surgery are PRK (photorefractive keratectomy) and phakic intraocular lens implantation. Some of the corneal refractive surgeries include:
-
LASIK: The ocular surface, refractive error, aberrations, pupil size, corneal size, and thickness are evaluated before the procedure. The surgeon applies eye drops to numb the eyes, asks the patient to relax, and places an instrument around the eyes to keep the eyelids open. A thin flap is created in the cornea using a microkeratome or a femtosecond laser, which helps the surgeon work more precisely and minimize complications. After the flap is created, the cornea is reshaped using an excimer laser, and the edges are smoothened. The flap is then gently placed back to its normal position; it attaches on its own in two to three minutes. After the procedure, the surgeon recommends certain eye drops and a shield to be worn over the eye for a few days and while sleeping to promote healing.
-
Photorefractive Keratectomy: It is a lesser-known corneal refractive surgery that is similar to LASIK but can accommodate patients with a thinner cornea. The flap is not incised in this procedure. Instead, the corneal epithelium (thin outer layer of the cornea) is removed using a laser or a blade. The eyes are made numb by applying anesthetic eye drops, and an eyelid holder is placed to prevent the eye from blinking. The patient is asked to stare at a target light, and the cornea is reshaped. A bandage is placed over the eyes to support healing. The epithelium grows back within a few days, but the recovery time is slightly longer compared to LASIK surgery.
-
Smile (Small Incision Lenticule Extraction): It is a modern type of laser refractive surgery usually performed to treat myopia and astigmatism. The laser is programmed with specific measurements, and the eyes are made numb using the eye drops. The eyelid holder is placed to prevent blinking, and a suction ring is used to lift and flatten the cornea. The laser sculpts a lenticule (disc-shape) in the cornea, which is then extracted through a small incision of two to three millimeters in width, and the cornea is reshaped. The patient is asked to relax after the surgery; the vision may be blurred for a few days but will gradually improve as the healing occurs.
What Are the Complications of Corneal Refractive Surgery and How Are They Managed?
Some of the primary complications of corneal refractive surgery include:
-
Visual Aberrations: It is reported in about 20 to 22 percent of cases. It includes sensitivity to light and halos (bright circles around the light source) or glares around the light. Research suggests that visual disturbances usually tend to stabilize around three to six months following the procedure.
-
Dry Eyes: Postoperative dry eyes may occur in approximately three percent of patients and can be attributed to the structure of corneal epithelium, inflammation, damage to certain ocular cells during suction, or impaired corneal sensation to blink. Studies have reported dry eyes in the postoperative period following a SMILE surgery more than femtosecond LASIK surgery. Dry eyes following refractive surgeries can be managed by artificial tears, gels, or medications such as topical corticosteroids or oral tetracyclines.
-
Infectious Keratitis: It is the infection of the cornea, also called an infectious corneal ulcer, due to bacteria, viruses, or fungi. Infectious keratitis following a laser refractive surgery is usually rare and accounts for about one to two percent. However, if left untreated, it can be a potential vision-threatening complication. It can be managed by antifungal or antiviral eye drops, oral medications, artificial tear drops, or antibiotic ointments.
Intraoperative complications of SMILE surgery include:
-
Lenticule Formation: Lenticule creation may include complications such as incisional bleeding, subconjunctival hemorrhage, black spots, and the formation of an opaque bubble layer (OBL). Loss of suction can also occur in approximately six percent of cases due to sudden patient movement or eye contraction. Studies have speculated that operating the femtosecond laser in a fast mode can reduce the incidence of suction loss. If loss of suction occurs when around ten percent of the lenticule is cut, redocking and re-centration may be followed. If more than ten percent of the lenticule is cut, the procedure can be converted into a PRK or a LASIK surgery. OBL can be managed intraoperatively by massaging out the bubbles from the interface to promote long-term visual outcomes. Black spots occur because of the entrapment of air bubbles or debris between the cornea and the lens. This can be managed by cleaning the ocular surface or the lens, and it does not impact the visual outcome.
-
Corneal Abrasions: Peripheral corneal abrasions can occur in 5 to 6 percent of cases, typically due to excessive manipulation during the surgery, and are correlated with the surgeon’s expertise. Corneal abrasions can slow down the healing process and also increase the risk of infections or inflammation. It may heal by using bandage contact lenses or without any treatment.
-
Incisional Tears: It is a surgical wound or a tear that can occur in around ten percent of cases and is usually secondary to patient movement or an experienced surgeon. Incisional tears can be managed by artificial tears and a bandage contact lens post-operatively; these do not affect the visual outcome.
Conclusion
An interprofessional team of eye surgeons, optometrists, nurses, and technicians are involved in the preoperative evaluation, surgery, and post-operative management of patients with refractive errors. Though refractive surgeries are effective, minimally invasive, and less time-consuming, they may be associated with certain drawbacks. Patients are also instructed to follow the post-operative instructions and contact the eye surgeon immediately if they experience any difficulties. Ensuring appropriate techniques, patient selection, and adequate follow-up can help in preventing complications.
