Intracorneal Ring Segments
● Two tiny clear crescent-shaped pieces of PMMA 150 degree inserted into the
cornea
● Placed in mid-corneal peripheral stroma at approximately 2⁄3 depth outside
central optical zone to reshape anterior corneal surface while maintaining
prolate profile (positive asphericity) of cornea
● Act as spacer elements between the bundles of corneal lamellae producing a
shortening of the central arc length (arc shortening effect) that is proportional to
thickness of device
● Central portion of anterior corneal surface tends to flatten and peripheral
area adjacent to ring insertion is displaced forward
Most common type of ICRS : INTACS
Hexagonal transverse shape - 8.1 mm external & 6.8 mm internal diameter
Refractive effect is modulated by thickness (0.25-0.45 mm, with 0.05-mm increments)- current designs have a predicted myopic range of correction from -1.00 to -4.10 D
Incision made with femtosecond laser or mechanically with a diamond knife and a tunnel created by a dissector into which the ring segments are placed
Other types: Ferrara rings, KeraRing, MyoRing, Bisantis Segments
Requirements: Age >21 years
Clear, central cornea
Minimum corneal thickness of 450 microns at incision site
Mesopic pupil size of less than 6 mm
Indications:
Low myopia
Progressive keratoconus
Ectasia after LASIK
Residual myopia after LASIK
Pellucid marginal degeneration
Contraindications:
● Keratoconus patients who can achieve functional vision on a daily basis using contact lenses
● Age <21 y
● Dont have clear central corneas
● Corneal thickness < 450 μ at proposed incision site
● Patients with collagen vascular/autoimmune diseases
● Ocular conditions - recurrent corneal erosions, corneal dystrophy
● Systemic diseases which affect wound healing -diabetes
Advantages:
● Leaves central cornea undisturbed
● Rapid results, predictable
● Reversible
● Corneal asphericity is maintained with minimal adverse effects
Complications:
● Epithelial defects
● Channel haze
● Under/ Over-corrections
● Sterile infiltrates/ epithelial cysts
● Ring extrusion
● Cornea thinning
● Infectious keratitis
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