eMedicine Specialties > Ophthalmology > Refractive Disorders

Hyperopia and Presbyopia, Conductive Keratoplasty

Author: Manolette R Roque, MD, MBA, DPBO, FPAO, President and CEO, Chief of Service, Ocular Immunology and Uveitis, Consulting Staff, Cornea and Refractive Surgery, Eye Republic Ophthalmology Clinic; General Manager, Ophthalmic Consultants Philippines Co; Consulting Staff, CME Liaison, Section Chief of Ocular Immunology and Uveitis, Department of Ophthalmology, Asian Hospital and Medical Center
Coauthor(s): Barbara L Roque, MD, Full Partner, Ophthalmic Consultants Philippines Co, Chief of Service, Pediatric Ophthalmology and Strabismus, Consulting Staff, Orbit and Eye Plastics, Eye Republic Ophthalmology Clinic; Ruben Limbonsiong, MD, Chief of Service, Refractive Surgery Service and Vision Laser Center, St. Luke's Medical Center; Program Director, Clinical Assistant Professor, Department of Ophthalmology, University of the Philippines at Manila; Roberto Pineda, ll, MD, Scholar, The Academy at Harvard Medical School; Director, Refractive Surgery Service, Massachusetts Eye and Ear Infirmary
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Updated: Oct 24, 2008

Introduction

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.^1,2,3,4,5,6 For this article, the discussion is limited to CK.

The history of CK for hyperopia began with Svyatoslav Fyodorov, MD, the inventor of radial keratotomy (RK). Fyodorov inserted a hot needle (nickel-chromium probe) at the peripheral cornea to induce shrinkage. This procedure was called hot needle keratoplasty; others referred to it as hot needle in the eye or HNE. Fyodorov encountered problems with consistency and maintenance of the temperature because the temperature (heated to as high as 600° C) went down as the hot needle entered the cornea (to a desired depth of up to 90% of corneal thickness). 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:YAG laser, first successfully used by Theo Seiler, MD, in 1990 for contact laser thermal keratoplasty (LTK) for the correction of hyperopia of up to 5 diopters (D), which also eventually failed.

In 1995, Sunrise Technologies introduced its noncontact holmium laser (Hyperion LTK System) for hyperopic correction via 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.

Nonholmium types (CO₂ lasers and diode lasers) of laser thermokeratoplasty options appeared in the market, also resulting in positive but transient effects.

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 D in the United States and up to +5.00 D in Canada.^7,8,9

Mendez then discovered CK. This revolutionary procedure presents convincing advantages over hyperopic LASIK and hyperopic correction via LTK.¹⁰ 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.^11,12,13,14
 
See related CME at LASIK Mostly Effective in Long-Term for Myopia of More Than -10 Diopter.

Problem

The central problem in the correction of hyperopia and presbyopia is the pressing challenge of steepening the central cornea.¹⁵

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).¹⁶ 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).¹⁷

Hyperopia

The Food and Drug Administration (FDA) Phase III clinical trials for CK included the following investigators: Asbell, McDonald, Maloney, Davidorf, Hersh, Manche, and Durrie.¹⁸ 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 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.

Presbyopia

The FDA Phase III clinical trials for presbyopic application of CK included the following investigators: McDonald, Durrie, Asbell, Maloney, and Nichamin.¹⁹ The study was a prospective multicenter clinical trial to evaluate CK for the treatment of presbyopic symptoms in emmetropic and hyperopic eyes.

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. Presbyopia is a natural part of the aging process and affects everyone.

Pathophysiology

In CK, a controlled release of radiofrequency energy is delivered intrastromally via a probe tip (450 µm X 90 µm). Impedance of the corneal tissue results in a thermal effect.^20,21 Thermal profile is homogeneous to approximately 80% of the depth of the cornea. The CK footprint has an average width of 405 µm and an average depth of 509 µm, as measured with ultrasonic biomicroscopy.

Presentation

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.

Indications

Hyperopic indications

The basis for the initiation of CK as a surgical procedure includes hyperopia. Hyperopia, commonly referred to as farsightedness, is an error of refraction (EOR) in which an individual may not have any difficulty seeing objects that are distant but may have problems focusing on objects that are near. In some instances, farsighted individuals can see all objects clearly, but they notice the need to strain the eyes, albeit unnecessarily, to maintain focus.

This type of EOR occurs when the eyeball is too short or when the cornea is too flat. In hyperopia, rays of light focus behind the retina instead of on it. This results in poor vision because the focus of light is not directly on the retina where it should be for normal vision. This anatomical structure induces a constant physiologic attempt to make up for the problem and to focus images. Symptoms of hyperopia involve asthenopia, which can include eyestrain, blurred vision, or headache (especially when reading or at the end of the day). These symptoms can increase over time.

Farsightedness (hyperopia) is often confused with presbyopia, which is a normal development of the aging process. Presbyopia occurs when the lens inside the eye loses flexibility, thereby preventing accurate focusing on nearby objects. This condition is common in individuals by the age of 40 years, and all persons older than 50 years experience presbyopia. People with this condition may experience eye strain/fatigue when reading in poor lighting conditions or at the end of the day, have trouble (slow) in changing focus from distance to near, or need to constantly reposition (move away) reading material in an attempt to find the correct focus.^22,23

CK hyperopic indications for use, as approved by the FDA, are as follows¹⁸ :

• CK treatment for the reduction of spherical hyperopia in the range of +0.75 D to +3.25 D of cycloplegic spherical hyperopia, with -0.75 D or less of refractive astigmatism, yielding +0.75 D to +3.00 D cycloplegic spherical equivalent
• CK treatment in patients with less than or equal to 0.50 D difference between preoperative manifest and cycloplegic refractions
• CK treatment in patients aged 40 years and older

Presbyopic indications

FDA supplemental approval of Refractec ViewPoint® CK System is for the temporary induction of myopia (-1.00 D to -2.00 D) to improve near vision in the nondominant eye of presbyopic hyperopes or presbyopic emmetropes, as follows¹⁹ :

• Via spherical hyperopic treatment of 1.00 D to 2.25 D
• In patients 40 years or older with a documented stability of refraction for the prior 12 months
• As demonstrated by a change of less than 0.50 D in spherical and cylindrical components of the manifest refraction
• With less than or equal to 0.75 D of cycloplegic refractive cylinder and with a successful preoperative trial of monovision or history of monovision wear (ie, dominant eye corrected for distance vision and nondominant eye corrected for near vision)

CK is an elective procedure with the alternatives including, but not limited to, the following:

• Reading glasses
• Bifocal eyeglasses
• Multifocal contact lenses
• Monovision contact lens wear
• Other refractive surgeries

Additional selection criteria

Suggested additional initial patient selection criteria for CK are as follows:

• Healthy, virgin cornea^24,25,26
• Corneal pachymetry at least 560 µm at 6 mm
• Corneal curvature between 41-44 D
• Patient tolerance for monovision
• Accurate determination of eye dominance
• Good corrected binocular vision
• No implanted regulating medical devices
• Patient understanding that presbyopia is progressive, with the probability of requiring additional treatments in the future

Relevant Anatomy

In hyperopia, the axial length (measurement of the most anterior part of the cornea to the most posterior part of the sclera) of the eyeball is generally shorter than normal and/or the corneal diopteric strength is weaker (flatter curvature).

A transparent avascular tissue, the cornea is continuous with the opaque sclera and the semitransparent conjunctiva. The cornea is covered by tear film on its anterior surface and bathed by aqueous humor on its posterior surface.

In adults, the cornea measures 11-12 mm horizontally and 9-11 mm vertically. The average corneal thickness is 0.5 mm (500 µm) centrally and 0.7 mm (700 µm) peripherally.

Contraindications

Patients must meet the inclusion criteria to be considered a good candidate for CK. A few relative contraindications (exclusion criteria) exist for CK.

• Younger than 21 years
• Drastic changes in vision or eyeglass prescription within the past year.
• Ophthalmoscopic signs of progressive or unstable hyperopia
• Eye conditions, including the following: (1) anterior segment pathology, including +2NS cataracts; (2) residual, recurrent, active ocular or uncontrolled eyelid disease, or any corneal abnormality (ie, recurrent corneal erosion, severe basement membrane disease); (3) recurrent history of herpes zoster or herpes simplex keratitis; (4) glaucoma (steroid responsiveness, ocular hypertension, risk for angle closure, or with potentially occludable angles); (5) intractable keratoconjunctivitis sicca; (6) known hypersensitivity to concomitant medications; and (7) peripheral pachymetry reading of less than 560 µm (at 6 mm optical zone).
• Patient who underwent strabismus surgery or may develop strabismus after the CK procedure
• Physical conditions, including the following: (1) diabetes, diagnosed autoimmune disease, connective tissue disease, or clinically significant atopic syndrome; (2) pregnancy, breastfeeding, or plans of pregnancy; and (3) keloid formation history
• Use of systemic medications with significant ocular adverse effects
• Use of chronic systemic corticosteroid or other immunosuppressive therapy that may affect wound healing
• Any immunocompromised patients
• Patients who are using ophthalmic medications other than artificial tears for treatment of any ocular pathology
• Patients with implantable electrical devices (eg, pacemakers, defibrillators, cochlear implants)

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