Although nonsurgical correction (ie, glasses, contact lenses) for patients with low-level hyperopia and presbyopia has been widely successful throughout the world, the surgical correctional procedures have been somewhat less accepted. (See History of the Procedure.) Conductive keratoplasty (CK), an advanced method for vision correction using controlled-release radiofrequency energy to gently reshape the cornea and to provide long-lasting vision correction, is now available for these patients.

History of the Procedure: Laser and laserlike surgical procedures for the correction of hyperopia have a checkered history. For this article, the discussion is limited to CK.

The history of CK for hyperopia began with Fyodorov, the inventor of radial keratotomy (RK). He inserted a hot needle at the peripheral cornea to induce shrinkage. This procedure was called hot needle keratoplasty; others referred to it as HNE (hot needle in the eye). Fyodorov encountered problems with consistency and maintenance of the temperature because the temperature went down as the hot needle entered the cornea. A scorching sound was produced each time the needle was applied on the cornea. The procedure resulted in an uneven application of heat, with the external cornea receiving more heat than the inner cornea. Summit laser then introduced its Holmium laser for contact laser thermal keratoplasty, which also failed. Early attempts with hyperopic photorefractive keratectomy (HPRK) were besieged by haze and regression.

The aforementioned procedures were successful in correcting some degree of hyperopia; however, long-term stability, vision quality, and patient comfort were not properly addressed. They were all instrumental as building blocks for the success of hyperopic laser in situ keratomileusis (LASIK), which currently provides excellent outcomes for low levels of hyperopia; low levels of hyperopia are classified as +3.00 diopters (D) in the United States and up to +5.00 D in Canada.

In 1995, Sunrise introduced its noncontact Holmium laser for hyperopic correction via laser thermal keratoplasty (LTK). The problems that beset this particular technology were also related to the regression associated with the unequal distribution of energy from the base to the apex.

Mendez then discovered CK. This revolutionary procedure presents convincing advantages over hyperopic LASIK and hyperopic correction via LTK. CK uses high radiofrequency energy that is delivered with a thin metal tip in concentric rings of multiple spots around the corneal periphery, shrinking collagen and steepening the central cornea. Refractec manufactures and markets this technology.

Problem: The central problem in the correction of hyperopia and presbyopia is the pressing challenge of steepening the central cornea.

Current treatment modalities include excimer laser ablation of the corneal periphery via either photorefractive keratoplasty (PRK) or LASIK and shrinkage of collagen in a circular pattern in the corneal periphery (eg, LTK). Hyperopic LASIK has been described as widely successful for low levels of hyperopia; however, the risk of flap-related complications cannot be overlooked. Thermal keratoplasty alters corneal curvature by heating the stromal tissue and causing the shrinkage of collagen. An optimal collagen shrinkage profile is currently acceptable. Previous experience has shown that too low of a heat causes minimal effect, while excessive heat causes remodeling and regression of effect. Two methods of collagen shrinkage are available: application of laser energy (ie, LTK) and application of radiofrequency energy (ie, CK).

The Food and Drug Administration (FDA) Phase III clinical trials for CK included the following investigators: Penny A. Asbell, Marguerite McDonald, Robert K. Maloney, Jonathan Davidorf, Peter Hersh, Edward E. Manche, and Daniel Durrie. The study was a prospective multicenter clinical trial to evaluate both the safety and the effectiveness of the ViewPoint CK system for the correction of hyperopia using the CK procedure. The study design was consistent with FDA guidance for refractive surgery lasers (September 1997) and draft American National Standards Institute (ANSI) guidance regarding laser systems for corneal reshaping.

The aim of the study was for a full correction of spherical hyperopia (ie, target of plano). All the treatments were based on preoperative cycloplegic refraction spherical equivalent (CRSE). Eligible patients for the study included those in the range of +0.75 D to +3.25 D of spherical hyperopia, with -0.75 D or less of refractive cylinder, yielding +0.75 D to +3.00 D cycloplegic spherical equivalent.

The effective parameters included improvement in uncorrected visual acuity (UCVA), predictability, stability, and patient satisfaction.

Frequency: Although numerous figures are reported in publications, the exact number of hyperopes in the world is unknown. Generally, hyperopia is believed to affect millions of persons in the United States and hundreds of millions of individuals around the world.

Of those individuals older than 50 years, 100% of them need corrective lenses for presbyopia.

Etiology: Errors in refraction may be inherited, and hyperopia may run in families.

Pathophysiology: In CK, a controlled release of radiofrequency energy is delivered intrastromally via a probe tip (450 mm X 90 mm). Impedance of the corneal tissue results in a thermal effect. Thermal profile is homogeneous to approximately 80% of the depth of the cornea. The CK footprint has an average width of 405 mm and an average depth of 509 mm, as measured with ultrasonic biomicroscopy.

Clinical: At some point, most, if not all, patients with hyperopia complain of a reduction in vision. The degree of blur depends on the amount of refractive error present. Both near vision and distance vision may be affected. Age may affect the reduction in visual performance. Patients with mild hyperopia, who function well prior to the presbyopic years, begin to experience difficulty with near work once their age approaches 40 years. Visual improvement is excellent with appropriate correction.