Intrastromal corneal ring segments
Encyclopedia
Intrastromal corneal rings (or intracorneal rings) are small devices implanted in the eye
to correct vision
. A typical vision correction using corneal rings would involve an ophthalmologist making a small incision in the cornea
of the eye, and inserting two crescent or semi-circular shaped ring segments between the layers of the corneal stroma, one on each side of the pupil
. The embedding of the rings in the cornea has the effect of flattening the cornea and changing the refraction
of light passing through the cornea on its way into the eye.
Corneal rings are typically used for patients with mild to moderate myopia
(-1.0 to -3.0 diopters of correction and 1.0 diopter or less of astigmatism
). An advantage over other surgical vision correction procedures like PRK
or LASIK
is that the implants are removable, which could allow for reversal or partial reversal of the correction, or replacement with different rings to change the amount of correction. Additional advantages are a lower risk of side effects, and a greater success rate of achieving the desired correction.
Potential complications are similar to other surgical vision correction procedures, and include infection
and vision distortions, particularly problems with night vision.
The ring segments themselves are made of PMMA (an acrylic glass
more commonly known under the tradenames Perspex or Plexiglas). The leading manufacturer is Addition Technology, which markets the rings under the trade name Intacs.
With the advent of wavefront LASIK and Implantable Collamer Lenses, Intacs or Implantable Corneal ring segments are rarely used for the correction of myopia. Intacs is the only FDA approved intracorneal ring segment. Today they are mainly used for the treatment of Keratoconus
. In June 2004 FDA approved them for the management of keratoconus. In April 2010 the FDA approved the expanded range of Intacs.
The intacs have to be placed in a channel in the cornea. This is best accomplished by a corneal surgeon. The channel can be created mechanically by an automated instrument or by femtosecond laser like intralase
. The ring segments are then implanted in these channels. The ring segments come in different thickness. Intacs can vary in thickness from 210 to 450 micrometres. They are placed around 7 mm from the optical center. A suture is placed at the entrance of the channels after the implantation of the Intacs.
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
to correct vision
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
. A typical vision correction using corneal rings would involve an ophthalmologist making a small incision in the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
of the eye, and inserting two crescent or semi-circular shaped ring segments between the layers of the corneal stroma, one on each side of the pupil
Pupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
. The embedding of the rings in the cornea has the effect of flattening the cornea and changing the refraction
Refraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
of light passing through the cornea on its way into the eye.
Corneal rings are typically used for patients with mild to moderate myopia
Myopia
Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...
(-1.0 to -3.0 diopters of correction and 1.0 diopter or less of astigmatism
Astigmatism
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances...
). An advantage over other surgical vision correction procedures like PRK
Photorefractive keratectomy
Photorefractive keratectomy and Laser-Assisted Sub-Epithelial Keratectomy are laser eye surgery procedures intended to correct a person's vision, reducing dependency on glasses or contact lenses. The first PRK procedure was performed in 1987 by Dr. Theo Seiler, then at the Free University...
or LASIK
LASIK
LASIK or Lasik , commonly referred to simply as laser eye surgery, is a type of refractive surgery for correcting myopia, hyperopia, and astigmatism...
is that the implants are removable, which could allow for reversal or partial reversal of the correction, or replacement with different rings to change the amount of correction. Additional advantages are a lower risk of side effects, and a greater success rate of achieving the desired correction.
Potential complications are similar to other surgical vision correction procedures, and include infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
and vision distortions, particularly problems with night vision.
The ring segments themselves are made of PMMA (an acrylic glass
Acrylic glass
Poly is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. It is sometimes called acrylic glass. Chemically, it is the synthetic polymer of methyl methacrylate...
more commonly known under the tradenames Perspex or Plexiglas). The leading manufacturer is Addition Technology, which markets the rings under the trade name Intacs.
With the advent of wavefront LASIK and Implantable Collamer Lenses, Intacs or Implantable Corneal ring segments are rarely used for the correction of myopia. Intacs is the only FDA approved intracorneal ring segment. Today they are mainly used for the treatment of Keratoconus
Keratoconus
Keratoconus , is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve....
. In June 2004 FDA approved them for the management of keratoconus. In April 2010 the FDA approved the expanded range of Intacs.
The intacs have to be placed in a channel in the cornea. This is best accomplished by a corneal surgeon. The channel can be created mechanically by an automated instrument or by femtosecond laser like intralase
IntraLase
IntraLase was a company based in Irvine, California, producing lasers for the medical industry and for eye surgery. In March 2007 it was acquired by Advanced Medical Optics for $800 million in cash. Advanced Medical Optics was acquired by Abbott Laboratories in February 2009...
. The ring segments are then implanted in these channels. The ring segments come in different thickness. Intacs can vary in thickness from 210 to 450 micrometres. They are placed around 7 mm from the optical center. A suture is placed at the entrance of the channels after the implantation of the Intacs.