An intrastromal corneal ring segment (ICRS) (also known as intrastromal corneal ring, corneal implant or corneal insert) is a small device surgically implanted in the cornea of the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

to correct

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

. Two crescent or semi-circular shaped ring segments are inserted between the layers of the corneal stroma, one on each side of the

pupil The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black becau ...

, This is intended to flatten the cornea and change the

refraction In physics, refraction is the redirection of a wave as it passes from one transmission medium, medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commo ...

of light passing through the cornea on its way into the eye.

Design

Intrastromal corneal ring segments have many different types and designs. Manufacturers include Intacs (US), Cornealring (Brazil), Mediphacos Keraring (Brazil), Ferrara ring (Brazil), Myoring (Austria) and Intraseg (UK).

Medical uses

Intrastromal corneal rings were originally used to treat mild

myopia Myopia, also known as near-sightedness and short-sightedness, is an eye condition where light from distant objects focuses in front of, instead of on, the retina. As a result, distant objects appear blurry, while close objects appear normal. ...

. For this purpose, they have largely been superseded by

excimer laser An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and micro ...

s, which have better accuracy. They are now mostly used to treat mild to moderate

keratoconus Keratoconus is an eye disorder in which the cornea, the transparent front part of the eye, gradually thins and bulges outward into a cone shape. This causes distorted vision, including blurry vision, double vision, increased nearsightedness, ...

. Intrastromal corneal rings were approved in 2004 by the

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...

for people with keratoconus who cannot adequately correct their vision with glasses or contact lenses, and for whom

corneal transplant Corneal transplantation, also known as corneal grafting, is a surgical procedure where a damaged or diseased cornea is replaced by Corneal button, donated corneal tissue (the graft). When the entire cornea is replaced it is known as penetrating ...

is the only other option. They were approved under the Humanitarian Device Exemption, which means the manufacturer did not have to demonstrate effectiveness. According to the FDA, these products should not be used by people who "can achieve functional vision on a daily basis using contact lenses."

References

{{Eye surgery Refractive surgeries