2020–2021 BCSC Basic and Clinical Science Course™
13 Refractive Surgery
Chapter 4: Onlays and Inlays
Intrastromal Corneal Ring Segments
The procedure involves creating a lamellar channel at approximately 70% stromal depth, followed by insertion of the ring segments. The geometric center of the cornea is marked with a blunt hook. An ultrasound pachymeter is used to measure the thickness of the cornea over the entry mark. A diamond knife is set to 70% of the stromal depth and then used to create a 1.0-mm radial incision. Specially designed mechanical instruments are then used to create the channels for the segments by blunt separation of the collagen lamellae (Fig 4-4). Similar entry incisions and channels may be created using a femtosecond laser (Video 4-1). The channels are created in an arc pattern at the desired inner and outer diameters. Once the channels are created, specialized forceps are used to insert the first ring segment and rotate it into position, followed by similar insertion and rotation of the second segment. Tissue glue or 10-0 nylon sutures may be used to close the radial incision at the corneal surface.
Implantation of asymmetric corneal ring segments for the surgical management of keratoconus. Courtesy of George O. Waring IV, MD.
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Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.