The ideal refractive surgery procedure is one that is effective, predictable, safe, and potentially reversible. The goal of this article is to introduce a fairly new refractive surgical procedure in which implantation of a polymethyl methacrylate (PMMA) ring or ring segments in the peripheral corneal stroma is used to correct myopia.

Device description

The KeraVision intrastromal corneal ring (ICR) is a device designed to correct mild-to-moderate myopia by flattening the anterior corneal curvature without encroaching on the visual axis. The device is an open-ended PMMA transparent ring with an outer diameter (R2) of 8.1 mm and an inner diameter (R1) of 6.8 mm. It is precision lathe-cut to ±0.01 mm as a hexagonal-shaped section of a cone with positioning holes for manipulation. It is inserted through a peripheral radial incision made with a diamond knife at two-thirds corneal depth in to a 360° peripheral intrastromal channel created with specially designed instruments. Anterior corneal curvature is changed by using rings of different thicknesses.

Intrastromal corneal ring segments (Intacs microthin prescription inserts), or ICRS, are a more recent design modification of the ICR. The ring segments split the ring into two 150° arcs. The use of ring segments simplifies the implantation procedure. Furthermore, ring segments can be placed away from the radial incision, thereby minimizing the potential for incision-related complications.

Surgical instruments

KeraVision has designed surgical instruments specifically for use with Intacs insertion. These include the following: corneal thickness gauges, glides, incision and placement marker, pocketing hook, pocketing lever, ring forceps, stromal spreader, vacuum-centering guide with vacuum system, and clockwise and counterclockwise dissectors.

Advantages of Intacs inserts

Several benefits of using Intacs microthin inserts exist. It is a minimally invasive outpatient procedure. Since the surgery is completed in the peripheral cornea, the central optical zone is not disturbed. Results are rapid and predictable. There is a reduced risk of visual side effects and a long-term convenient refractive correction. It is removable and exchangeable. Corneal asphericity (prolate) is maintained.

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