Advances in the Surgical Correction of Presbyopia

George O. Waring IV, MD; Duncan E. Berry, BA

Disclosures

Int Ophthalmol Clin. 2013;53(1):129-152. 

In This Article

Conductive Keratoplasty

History/Background

Over the years, a variety of methods have been used to induce refractive change by selective heating of the cornea, including radial thermal keratoplasty, holmium-YAG laser thermokeratoplasty, CO2 laser thermokeratoplasty, and diode laser thermokeratoplasty. Varying degrees of predictability and regression of effect have been reported in the aforementioned techniques.[31] The most recent incarnation of thermokeratoplasty developed by Mendez et al[32] is conductive keratoplasty. Conductive keratoplasty is the application of low-frequency radio waves to "shrink" collagen fibrils within the cornea. The low-frequency radio waves are delivered through a fine tipped probe applied to the corneal stroma. Corneal refractive change is produced by localizing the energy delivery to spots along a circumferential band in peripheral cornea. As the collagen shrinks, the band constricts and there is a steepening of the corneal curvature central to the band. The amount of corneal steepening is controlled by treatment placement, intensity, and duration. In theory, the energy delivery is self-limiting as denaturation of collagen increases resistance to the current flow.[33] The advantages of conductive keratoplasty over laser reshaping of the central cornea are that it preserves the optical clarity of the visual axis and does not involve any tissue removal. It is used to correct low to moderate levels of hyperopia and astigmatism in ammetropes as well as eyes made ammetropic because of LASIK or cataract surgery. More recently, it is also used to induce monovision in presbyopes.

Surgical Technique and Theory

The conductive keratoplasty system consists of a radiofrequency (RF) energy-generating console, reusable corneal marker, reusable lid speculum, reusable handpiece, disposable keratoplasty tip, and a foot pedal controller (Fig. 7). RF energy is set to 60% (0.6 W) with a 0.6-second treatment time. The lid speculum acts as the return electrode, so it is important to ensure it has direct contact with the eyelids. The keratoplasty tip has a 45-degree bend proximally to allow access to the eye over the brow or nasal region and a 90-degree bend distally to position the tip perpendicular to the corneal surface. A stop at 500 μm from the distal tip indicates the appropriate depth of tip penetration into the cornea. Conductive keratoplasty treatment spots are evenly spaced in a ring pattern of 6, 7, and/or 8 mm in diameter (Fig. 8). The number of treatment spots is determined by the desired correction (Table 1).[34] In standard conductive keratoplasty (CK), the probe tip depresses the corneal surface 5 to 7 mm while applying RF energy. This causes a mechanical stretching effect on the corneal fibers that resists the natural tendency of the tissue being drawn toward the pulse of RF energy. In LightTouch CK, pressure of the probe on the cornea is neutral, or about 2 mm. This low-compression technique may produce more robust results by minimizing the corneal stretching associated with the standard CK technique (Fig. 9).[35] A template (OptiPoint Corneal Template; Refractec Inc., Bloomington, MN) has also been developed to help standardize the CK technique. The template is a light-vacuum suction ring with holes for insertion of the RF tip. The template is centered on the estimated line of sight allowing accurate placement and depth of the probe tip. Thus, compression is limited as with the LightTouch technique, but the tip is still able to penetrate the stroma as in standard CK. In addition, template use allows for more predictable spot placement which reduces induced astigmatism.[36] The CK procedure can be performed under topical anesthesia. Once the desired correction has been determined and the treatment nomogram determined, the patient is placed supine under the operating microscope and the lid speculum inserted. With the patient fixating on a coaxial microscope light, the corneal surface is dried. The CK marker is dampened with gentian violet and centered over the cornea to mark the 6-, 7-, and 8-mm optical zones and the hash marks designating the positions for CK spot treatments. Centration of the marker on the estimated line of sight is crucial for effective CK treatment. Treatment spots are applied according to the surgical plan with special care taken to ensure appropriate pressure, tip placement, and tip orientation—normal to the corneal surface. After application of RF energy, remove the probe. Treatment spots should be placed with a regular cadence in the indicated order. The procedure should be efficient to avoid excessive corneal drying; aiming for 1 minute or less per series 8 spots.

Figure 7.

The ViewPoint conductive keratoplasty System (Refractec Inc. Bloomington, MN) consists of a radiofrequency energy-generating console, reusable corneal marker, reusable lid speculum, reusable handpiece, disposable keratoplasty tip, and a foot pedal controller. Source: Photo courtesy of Refractec Inc.

Figure 8.

Diagram of radiofrequency spot placements and the order in which the spots are to be applied. Treatment spots are placed at the intersection of the straight lines with each ring. For 16, 24, and 32 spot treatments, spots should be placed around the 6-mm ring first, followed by the 7-mm ring, and finally the 8-mm ring when necessary. The numbers indicate the order in which the treatment spots should be placed.

Figure 9.

In standard conductive keratoplasty (CK), the probe tip depresses the corneal surface 5 to 7mm while applying radiofrequency (RF) energy (B). This causes a mechanical stretching effect on the corneal fibers that resists the natural tendency of the tissue being drawn toward the pulse of RF energy. In LightTouch CK, pressure of the probe on the cornea is neutral, or about 2 mm (A). This low-compression technique may produce more robust results by minimizing the corneal stretching associated with the standard CK technique. Source: Photo courtesy of Refractec, Inc. Bloomington, MN.

Efficacy

One-year results from the FDA clinical trial for the use of CK to induce monovision as a treatment for presbyopia demonstrated J1 or better UCNVA for 38% (20/53) of eyes and J3 or better for 81% (43/53) of eyes treated for near vision. Binocular UCNVA of J1 or better was achieved by 47% (25/53) of patients and J3 or better by 89% (47/53) of patients. Binocular UCDVA was 20/20 or better for 97% (60/62) of patients and 20/40 or better for all patients (62/62). Combined binocular UCNVA and UCDVA are shown in Figure 10.[37] Ye and colleagues followed 27 patients who underwent CK for monovision as a correction of presbyopia. Mean UCNVA of the CK eye went from 0.92 (20/166)±0.16 before treatment to 0.30 (20/40)±0.13 12 months after treatment (P<0.05).[38] Stahl and colleagues reported longer-term data on 10 eyes of 10 patients who underwent CK in the nondominant eye to treat presbyopia. Preoperatively, 1 patient had binocular UCDVA of 20/30 or better and UCNVA of J5 or better. This improved at 1-year post-CK (n=10) to 8 patients with binocular UCDVA of 20/20 or better and J1 or better UCNVA. All patients had UCDVA 20/40 and UCNVA J3. At 3 years postoperative (n=9), 2 patients achieved 20/20 UCDVA and J1 UCNVA or better and 7 achieved 20/40 UCDVA and J3 UCNVA or better.[39,40] Conductive keratoplasty has also been used to correct hyperopic refractive error after cataract or refractive surgery.[41–43] Claramonte reported that after cataract surgery, only 25% of a group of 16 eyes achieved a UCDVA of 20/40 or better because of residual hyperopia. After refractive adjustment with CK, 62.5% of eyes had a UCDVA of 20/40 or better at 12 months postoperative.[41] Conductive keratoplasty in 39 eyes of 38 patients for the treatment of presbyopia with monovision demonstrated good refractive stability and predictability in eyes that had previously had LASIK surgery and eyes that had no previous surgery. The binocular outcomes at 1-year postoperative were similar for the post-LASIK and non-LASIK groups. After CK treatment in the nondominant eye, binocular mean UCDVA was -0.18±0.00(20/13) in the post-LASIK group and -0.09±0.12(20/16) in the non-LASIK group and mean UCNVA was 0.22±0.25(20/33) and 0.20±0.17(20/31), respectively.[43]

Figure 10.

Combined uncorrected distance and near visual acuities. Snellen score indicates minimum distance vision for group and Jaeger score indicates minimum near vision for each group. Source: US FDA. Refracted ViewPoint CK System.37

Safety

One of the advantages of CK is the safety of the procedure. Unlike LASIK, corneal manipulations with CK are peripheral. They do not directly affect the visual axis or ablate corneal tissue. Across 11 studies that reported safety as lines of best corrected visual acuity lost, 7 of a total of 770 eyes (1%) lost 2 lines of best corrected distance visual acuity (BCDVA).31,37,38,40,42,44–47 All 7 patients with a 2-line loss of BCDVA were part of the initial FDA clinical trial treating hyperopia, exceeding FDA safety standards.[44] Effects of the RF waves do not damage the corneal endothelium. Histologic changes are minimal in the endothelial layer and endothelial cell counts at the corneal periphery, mid-periphery, and centrally showed no significant change from preoperative values after 1 year of follow-up.[44,48] Contrast sensitivity is also spared with CK. Because the treatment zones are at the periphery of the cornea, postoperative contrast sensitivity measurements remain within normal limits.[38,44,46]

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