<unk>  corneal<unk> s (or intracorneal<unk> s) are small devices implanted in the eye to correct vision. A typical vision correction using corneal<unk> s would involve an ophthalmologist making a small incision in the cornea of the eye, and inserting two crescent or semi-circular shaped<unk><unk>  between the layers of the corneal stroma, one on each side of the pupil. The embedding of the<unk> s 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<unk> s are typically used for patients with mild to moderate nearsightedness (1 to 3 diopters of correction and 1 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<unk> s 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<unk><unk>  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<unk> s under the trade name Intacs.
Intrastromal corneal ring segments
Corneal neovascularization
Basement membrane corneal dystrophy
Macular edema
Interstitial keratitis
Epiretinal membrane
Pitted keratolysis
Vitreous humour