An intrastromal corneal ring segment (ICRS) (also known as intrastromal corneal ring, corneal implant or corneal insert) is a small device implanted in the eye 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 un ...

. The procedure involves an

ophthalmologist Ophthalmology ( ) is a surgery, surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Followin ...

who makes a small incision in the

cornea The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...

of the eye and inserts two crescent or semi-circular shaped ring segments between the layers of the corneal stroma, one on each side of the

pupil The pupil is a black 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 ...

. The embedding of the two rings in the cornea is intended to flatten the cornea and change the

refraction In physics, refraction is the redirection of a wave as it passes from one 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 commonly observed phenomeno ...

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

Design

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

Medical uses

Intrastromal corneal rings were originally used to treat mild

myopia Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...

. For this purpose, they have largely been superseded by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 microm ...

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

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 donated corneal tissue (the graft). When the entire cornea is replaced it is known as penetrating keratoplasty ...

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

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