April 23rd, 2012 by admin
Using heat to alter the cornea curvature was first introduced by Gayat in 1876 however, the new era of thermal keratoplasty first began in 1984 when Svyatoslav Fyodorovinserted a hot probe (nickel-chromium probe) in the peripheral cornea to induce shrinkage. Modern conductive keratoplasty (CK) was later developed by Mendezfor correction of hyperopia. His results were published in 1997. CK is a surgical technique aimed to alter the cornea curvature. CK uses a low-energy, radiofrequency (350 kHz) current to heat the peripheral cornea. This results in shrinkage of the peripheral stromal collagen, and therefore flattening the peripheral cornea, and steepening of the central cornea.
In 2002, CK using the Viewpoint system (Refractec, Inc, Irvine, Ca) received Food and Drug Aministration approval for temporary treatment of mild to moderate hyperopia (+0.75 to +3.0 D) with astigmatism of -0.75 D or less. In 2004, CK was FDA approved for treatment of presbyopia in the non-dominant eye of presbyopic patients with a target of -1.0 to -2.0 D.
CK is painless and is performed with a hand-held probe at the end of which is a disposable stainless steel tip that penetrates about 450 microns into the corneal stroma. The eyelid speculum is attached to the probe to allow for the electrical return path. In CK, a controlled release of radiofrequency energy is delivered intrastromally via a probe tip. Impedance of the corneal tissue results in local heat contraction of tissue that induces the shape change. Thermal profile is homogeneous to approximately 80% of the depth of the cornea. The CK footprint has an average width of 405 microns and an average depth of 509 microns. Its major advantage is the greater stability of the refractive effect compared to other forms of thermal keratoplasty. CK allows the surgeon to customize the astigmatism correction for each patient.
It is a novel concept to apply selective CK spots to the cornea for keratoconus in order to reduce astigmatism. This chapter will discuss CK for astigmatism in keratoconus. It is important to note that to reduce likelihood of complete regression, CK should be performed with C3-R® on the same day or on a cornea previously treated with C3-R®. Using CK in a cornea without C3-R® has a high rate of regression of the astigmatism effect.
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