What is myopia?

Myopia, or near-sightedness, is a common vision condition in which light entering the eye focuses in front of the retina rather than directly on it. As a result, distant objects appear blurry while close objects can be seen clearly. Myopia can be categorized into two types: refractive myopia, which results from excessive focusing power of the cornea or lens, and axial myopia, which is caused by an elongated eyeball.

Principles of Refractive Surgery

Refractive surgery encompasses a range of surgical procedures designed to reshape the cornea, enabling light to focus properly on the retina. These procedures are used to correct vision problems such as myopia (near-sightedness), hyperopia (far-sightedness), and astigmatism, often reducing or eliminating the need for glasses or contact lenses.

Diagram of the Cornea

The cornea contains many layers of cells, including the epithelium, anterior elastic lamina, stroma, Descemet’s membrane, and endothelium. Refractive surgery alters the curvature of the stroma, the primary structure of the cornea. This allows the cornea to focus light entering the eye directly on the retina. The epithelium regrows and heals after surgery to protect the cornea, whereas changes to the stroma are permanent, allowing vision correction to be permanent.

In myopia, the curvature of the cornea is too great, causing light to be focused ahead of the retina. Refractive surgery flattens the curvature of the cornea, projecting the light directly onto the retina.

Evolution of refractive surgery techniques

First generation: Photorefractive Keratectomy (PRK)

Photorefractive keratectomy (PRK) is a type of refractive surgery in which the outer layer of the cornea (the epithelium) is removed to expose the underlying corneal tissue. An excimer laser is then used to precisely reshape the cornea, correcting refractive errors without generating heat or damaging surrounding tissue. After the procedure, the epithelial layer naturally regenerates and gradually heals over the reshaped cornea. In conventional PRK, the epithelium is prepared with an alcohol solution and removed with a knife. In TransPRK, an excimer laser is used to both ablate the epithelium and sculpt the underlying cornea.

Conventional PRK

TransPRK

Second Generation: Laser-Assisted In Situ Keratomileusis

Laser-assisted in situ keratomileusis (LASIK) is the most commonly performed refractive surgery that involves creating a thin corneal flap using a femtosecond laser to expose the underlying stromal layer. An excimer laser is then used to precisely reshape the cornea, correcting refractive errors such as myopia, hyperopia, or astigmatism. Unlike PRK, LASIK preserves the outer corneal epithelial layer by repositioning the flap after the procedure, which typically results in less postoperative pain and a faster visual recovery.

Third generation: Keratorefractive Lenticule Extraction (KLEx)

Unlike PRK or LASIK, which reshape the cornea by ablating tissue, keratorefractive lenticule extraction (KLEx) uses a femtosecond laser to precisely cut a small, lens-shaped piece of corneal tissue (lenticule) within the stroma. This lenticule is then removed through a tiny incision, typically 2 to 4 mm in length, allowing for vision correction with minimal disruption to the corneal surface. KLEx is the newest class of refractive surgery.

Nobel Medical Group Services

SILK

Johnson & Johnson (USA) ELITA

Smooth incision lenticule keratomileusis (SILK) is a novel KLEx procedure powered by the ELITA laser system. SILK is the only procedure that generates a biconvex lenticle, which allows symmetric adhesion of both sides of the cornea after surgery. SILK also uses a high frequency laser that produces a smooth lenticular surface. Together, these innovations allow both sides of the cornea to join together smoothly without abberations or pockets after surgery.

IntraLase FS Laser

Johnson & Johnson (USA) IntraLase FS

The IntraLase femtosecond technology allows bladeless generation of a corneal flap.

Wavefront-guided LASIK

Johnson & Johnson (USA) iDESIGN Refractive Studio and STAR S4 IR Excimer

The iDESIGN Refractive Studio creates an enhanced topological map of the cornea for improved customization of the surgery and improved results, also known as Wavefront-Guided LASIK. The STAR S4 excimer laser system combines this topological map with its variable spot beam technology, which enables precise excimer laser pulses of variable size and energy to perform a customized adjustment to the patient’s cornea.