Journal of Refractive Surgery

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Conductive Keratoplasty for Presbyopia: 3-year Results

Jason E Stahl, MD

Abstract

ABSTRACT

PURPOSE: To assess the long-term safety, efficacy, and stability of conductive keratoplasty (CK) in the treatment of presbyopia.

METHODS: Ten near-piano presbyopic patients (6 women and 4 men) underwent unilateral CK with standardpressure technique in the non -dominant eye to improve their near vision. Mean age was 51 ?3.1 years (range: 46 to 56 years). Nine of the 10 patients were available for both 1- and 3-year follow-up examinations.

RESULTS: Preoperative mean manifest refraction spherical equivalent (MRSE) was -0.17?0.29 diopters (D), yielding a mean near uncorrected visual acuity (UCVA) of JlO. Three years after CK, the mean near UCVA was J3. The mean MRSE at 3 years was -1.06?0.81 D, which represents a 0.25 D change from the MRSE at 1 year. The MRSE in the dominant untreated eyes had a +0.26 D change during the 3-year period, which was not statistically different when compared to the CKtreated eyes during the 3-year postoperative period. No eye lost best spectacle-corrected visual acuity or had induced cylinder ^ 0.75 D. Seventy-eight percent had binocular distance UCVA 20/20 or better and near UCVA J3 or better. The average keratometry remained stable at 45.09 D 3 years postoperatively compared to 45.08 D 1 year postoperatively.

CONCLUSIONS: Conductive keratoplasty for the treatment of presbyopia provided safe, effective, predictable, and stable results 3 years following the initial surgery. Refractive stability was similar for both the CK-treated and untreated eyes with a small hyperopic shift noted during the 3-year follow-up period. [J Refract Surg. 2007;23:905-910.]

Abstract

ABSTRACT

PURPOSE: To assess the long-term safety, efficacy, and stability of conductive keratoplasty (CK) in the treatment of presbyopia.

METHODS: Ten near-piano presbyopic patients (6 women and 4 men) underwent unilateral CK with standardpressure technique in the non -dominant eye to improve their near vision. Mean age was 51 ?3.1 years (range: 46 to 56 years). Nine of the 10 patients were available for both 1- and 3-year follow-up examinations.

RESULTS: Preoperative mean manifest refraction spherical equivalent (MRSE) was -0.17?0.29 diopters (D), yielding a mean near uncorrected visual acuity (UCVA) of JlO. Three years after CK, the mean near UCVA was J3. The mean MRSE at 3 years was -1.06?0.81 D, which represents a 0.25 D change from the MRSE at 1 year. The MRSE in the dominant untreated eyes had a +0.26 D change during the 3-year period, which was not statistically different when compared to the CKtreated eyes during the 3-year postoperative period. No eye lost best spectacle-corrected visual acuity or had induced cylinder ^ 0.75 D. Seventy-eight percent had binocular distance UCVA 20/20 or better and near UCVA J3 or better. The average keratometry remained stable at 45.09 D 3 years postoperatively compared to 45.08 D 1 year postoperatively.

CONCLUSIONS: Conductive keratoplasty for the treatment of presbyopia provided safe, effective, predictable, and stable results 3 years following the initial surgery. Refractive stability was similar for both the CK-treated and untreated eyes with a small hyperopic shift noted during the 3-year follow-up period. [J Refract Surg. 2007;23:905-910.]

In 1898, Lans1 published animal experiments documenting that heating the peripheral cornea could induce central steepening. Over the next century, several thermokeratoplasty techniques were investigated. In the early 1990s, the first contact probe holmium yttrium-aluminumgarnet (Ho: Y AG) laser thermokeratoplasty (LTK) procedure (Summit Technologies, Waltham, Mass) was developed for the treatment of hyperopia.2 However, US Food and Drug Administration (FDA) clinical trials of Summit's contact LTK demonstrated poor predictability and regression of effect. In 2000, non-contact holmium LTK (Sunrise Technologies, Fremont, Calif) was FDA-approved for the treatment of hyperopia. The initial overcorrection and significant regression of effect has been problematic for this technique,3 and the instrument is no longer commercially available.

Conductive keratoplasty (CK) is a non-laser, radiofrequency-based thermal keratoplasty procedure that received FDA approval in 2002 for the treatment of spherical hyperopia4 and then in 2004 for the treatment of presbyopic symptoms of presbyopic hyperopes and emm?tropes.5"7 The ViewPoint CK system (R?fract?e Ine, Irvine, Calif) uses a probe to deliver radiofrequency energy that the cornea converts to heat in a controlled fashion.

Previous studies have demonstrated CK is a safe, effective, predictable, and stable procedure for up to 30 months for moderate hyperopia8 and for up to 1 year for presbyopia.7 This article presents the 3 -year postoperative results of CK performed in the non-dominant eye of piano presbyopic patients for near vision improvement.

Table

TABLE 1Preoperative, Surgical, 1-year, and 3-year Postoperative Data on 10 Eyes Treated With Conductive Keratoplasty for Presbyopia

TABLE 1

Preoperative, Surgical, 1-year, and 3-year Postoperative Data on 10 Eyes Treated With Conductive Keratoplasty for Presbyopia

Table

TABLE 1Preoperative, Surgical, 1-year, and 3-year Postoperative Data on 10 Eyes Treated With Conductive Keratoplasty for Presbyopia

TABLE 1

Preoperative, Surgical, 1-year, and 3-year Postoperative Data on 10 Eyes Treated With Conductive Keratoplasty for Presbyopia

PATIENTS AND METHODS

In this prospective, consecutive case series, singlecenter clinical study, 10 eyes of 10 patients (6 women and 4 men) were treated for presbyopia with CK. The treatment was performed with the Vie wP oint CK system (R?fract?e Ine). Informed consent was obtained from each patient prior to surgery. Mean patient age was 51?3.1 years (range: 46 to 56 years). Eligibility criteria have been described previously.7

Sighting dominance testing determined the patient's eye dominance and has been described previously.7 Dominance testing is important in mono vision procedures for patients of this piano presbyopic group, as they have excellent uncorrected visual acuity (UCVA) and they will be using their dominant eye for distance viewing.

Each patient's near UCVA was measured at 14 inches using the Alza near vision card (Palo Alto, Calif). Loose lens (+0.75 to +1.50 D) testing of the non-dominant eye, as described previously,7 determined how many rings of treatment (one or two) would be performed. The loose lens is held in front of the non-dominant eye while binocularly viewing first the near card and then the distance chart to determine patient satisfaction with both near and distance visual acuity.

Conductive Keratoplasty Surgical Procedure

The standard-pressure CK technique was performed in all eyes as described previously.7 All eyes were treated at the default setting of 350 kHz, 60% power, for 0.6 seconds. Nine eyes received a total of 16 spots with 8 spots placed at both the 6- and 7-mm treatment zones. One eye, with a past history of hyperopia LASIK, received a total of 8 spots at the 6-mm treatment zone. A target refraction of ?1.25 to ?1.75 D in the non-dominant eye was selected depending on the patient's near visual needs.

POSTOPERATIVE CARE

Early postoperative care has been described previously.7 Postoperative data were obtained during examinations at 3 months and 1 and 3 years. Patients were asked to complete a questionnaire at the 3-year examination to evaluate the quality of their vision, report their level of satisfaction, and indicate whether spectacle correction was needed for either near or distance vision. No retreatments were performed during the 3 years following the initial CK procedure.

STATISTICAL ANALYSIS

Statistical analysis of the results was performed as means, standard deviations (SD), ranges, and 95% confidence intervals. Temporal differences between results were analyzed similarly, with P values calculated using the paired t test. P values <.05 were considered statistically significant.

Statistical analysis of astigmatic results was performed using vector analysis to calculate means and 68% predictive (SD) ellipses and equivalent-area circles. Temporal differences between results were analyzed similarly, with P values calculated using Hotelling's one-sample Tsquare test on the differences.

RESULTS

In this study, 10 eyes of 10 near-piano presbyopic patients treated with CK for near vision improvement underwent follow-up for 3 years. Nine patients were available for follow-up examination at 3 years; results for these 9 patients are summarized in the Table. The patient who had a single ring of 8 CK spots in an eye with a history of hyperopic LASIK was lost to follow-up.

UNCORRECTED VISUAL ACUITY

Preoperative and postoperative near UCVA measurements for the treated eyes are shown in Figure 1. Preoperatively, mean near UCVA was JlO (range: Jl 2 to J5). One year postoperatively, mean near UCVA was Jl (range: J3 to Jl), with 89% of eyes Jl and 100% of eyes J3. Three years postoperatively, mean near UCVA was J3 (range: J8 to Jl), with 22% of eyes Jl, 33% of eyes J2 or better, 78% of eyes J3 or better, and 100% of eyes J8 or better.

Preoperatively, mean logMAR distance UCVA was 20/22?0.07 (range: 20/30 to 20/20). One year postoperatively, mean distance UCVA was 20/36?0.17 (range: 20/60 to 20/20). Three years postoperatively, mean distance UCVA was 20/41?0.30 (range: 20/100 to 20/20).

Preoperatively, 1 (11%) patient had binocular distance UCVA 20/30 or better and near vision J5 or better. One year postoperatively, 8 (89%) patients had binocular uncorrected distance vision 20/20 or better and near vision Jl or better; all 9 (100%) patients had binocular distance UCVA 20/20 or better and near vision J3 or better. Three years postoperatively, 2 (22%) patients had binocular distance UCVA 20/20 or better and near UCVA Jl or better, and 7 (78%) patients had binocular distance UCVA 20/20 or better and near UCVA J3 or better (Fig 2). Mean logMAR binocular distance UCVA was 20/20 at 1 year and 20/19 at 3 years postoperatively.

REFRACTIVE OUTCOME AND SAFETY

Preoperatively, mean MRSE was -0.17?0.29 D (range: +0.25 to -0.75 D), mean sphere was 0.03?0.34 D (range: +0.50 to ?0.25 D), and mean cylinder was -0.39?0.31 D (range: piano to -1.00 D). One year postoperatively, mean MRSE was ? 1.31?0.53 D (range: -0.75 to -2.25 D), mean sphere was -1.00?0.47 D (range: ?0.50 to ?1.75 D), and mean cylinder was -0.61?0.22 D (range: -0.50 to -1.00 D). Three years postoperatively, mean MRSE was ? 1.06?0.81D (range: piano to -2.75 D), mean sphere was -0.83?0.65 D (range: piano to ?2.25 D), and mean cylinder was -0.44?0.53 D (range: piano to -1.50 D). There was a statistically significant difference in MRSE between preoperative and all postoperative examinations, including 3 years postoperatively (P=. 0041).

The absolute change in refractive cylinder was 0.22 D (range: 0 to 0.50 D) and 0.06 D (range: 0 to 0.75 D) 1 and 3 years postoperatively, respectively. There was no significant change in cylinder from preoperative to 3 months (P=.186), from 3 months to 1 year (P=.505), from 1 year to 3 years (P=. 468), or from preoperative to 3 years (P=. 523). No eye had an increase in cylinder 2^0.75 D at 3 years following surgery. The logMAR best spectacle-corrected visual acuity (BSCVA) was 20/20 for all eyes prior to surgery; at the 1- and 3-year postoperative examinations, no eye had lost lines of BSCVA.

Figure 1. Preoperative and 1- and 3-year postoperative uncorrected near visual acuity (Jaeger) in nine eyes that underwent conductive keratoplasty for near vision improvement.Figure 2. Preoperative and 1- and 3-year postoperative binocular uncorrected visual acuity at near (Jaeger) and distance (Snellen) for nine eyes that underwent conductive keratoplasty for presbyopia.

Figure 1. Preoperative and 1- and 3-year postoperative uncorrected near visual acuity (Jaeger) in nine eyes that underwent conductive keratoplasty for near vision improvement.

Figure 2. Preoperative and 1- and 3-year postoperative binocular uncorrected visual acuity at near (Jaeger) and distance (Snellen) for nine eyes that underwent conductive keratoplasty for presbyopia.

Figure 3. Mean diopter change in manifest refraction spherical equivalent over 3 years of follow-up for nine eyes that underwent conductive keratoplasty.

Figure 3. Mean diopter change in manifest refraction spherical equivalent over 3 years of follow-up for nine eyes that underwent conductive keratoplasty.

STABILITY

All nine CK-treated eyes were evaluated for stability (mean diopter change in MRSE over time) (Fig 3). There was no significant change in MRSE between 1 and 3 years postoperatively (P=. 1281). The 3-year mean MRSE was ?1.06 D, which represented a 0.2 5 -D decrease from the mean MRSE of ?1.31 D at 1 year. The rate of change (as indicated by the change in diopters per month) was 0.01 D per month.

Interestingly, the mean MRSE of the dominant non-treated eyes changed from ?0.11 D at the preoperative examination to +0.15 D at the 3-year postoperative examination, representing a change of +0.26 D during the 3 years. The average change per year was + 0.09 D. The +0.18 D change during the 2-year period in the non-treated eyes was not significantly different than the change (+0.25 D) in CK-treated eyes during the 1- to 3-year follow-up period (P=. 289).

PREDICTABILITY

All eyes were targeted for ?1.25 D postoperative refraction except one eye that was targeted for ?1.75 D. The target was based on loose lens testing and patient satisfaction with near vision during this test. Three years postoperatively, 100% of eyes were within ? 1.00 D, 78% were within ?0.75 D, 44% were within ?0.50 D, and 22% of eyes were within ?0.25 D of intended correction.

KERATOMETRY

Preoperative mean keratometry on videokeratography was 43.5 ?1.84 D. The mean keratometry was significantly steeper at both 1 year (45.08?2.10 D) and 3 years (45.09?1.89 D) (P<.0001). There was no significant change in keratometry from 1 to 3 years postoperatively (P=. 56), which indicates no regression of CK's corneal tightening (steepening) effect. The mean keratometry change from preoperative to 3 years was 1.66 D of steepening that resulted in a mean refractive effect (postoperative mean MRSE minus preoperative mean MRSE) of - 1 . 00 D .

Slit-Lamp Findings and Anterior Segment Imaging

Three years postoperatively, faint CK spots were still present on slit-lamp examination. The spots were less dense but the stromal depth was still approximately 70% to 80% of corneal thickness as demonstrated on anterior segment optical coherence tomography (Fig 4).

Figure 4. Anterior segment optical coherence tomography image demonstrating adjacent conductive keratoplasty spots that extend approximately 70% to 80% of stromal thickness 3 years postoperatively.

Figure 4. Anterior segment optical coherence tomography image demonstrating adjacent conductive keratoplasty spots that extend approximately 70% to 80% of stromal thickness 3 years postoperatively.

COMPLICATIONS

No complications occurred during the surgeries or postoperatively in the study.

PATIENT COMMENTS

Patients were asked to complete a short questionnaire at the 3-year examination. Patients reported satisfaction with the CK procedure and indicated they would have the procedure again and also would recommend the procedure to others. When asked what percentage of time they used reading glasses, the average was 23% (range: 0% to 100%). Only one patient reported using spectacles 10% of the time for improved distance vision, which represents an average of 1.4% (range: 0% to 10%). Patients reported CK helped their effectiveness with their job and daily activities. Patients also reported their overall vision following CK was better than they expected before surgery.

DISCUSSION

The participating patients, ranging in age from 46 to 56 years at the time of CK, had all presented seeking decreased dependence on reading glasses. Their spherical and cylindrical refractive error was low, placing them in the category of piano presbyopes, defined as having an MRSE of ?0.75 D of emmetropia with ^1.00 D cylinder, who are at least 45 years of age, and have significant presbyopic symptoms. None of the patients in this study required distance correction. The patients' binocular distance UCVA was 20/20 in all cases, but binocular near UCVA confirmed their presbyopic condition.

EFFICACY

All patients achieved improved uncorrected near vision after CK treatment that continued during the 3 years of follow-up. The achieved efficacy of J3 or better near UCVA in 100% of patients, with 89% of patients reading Jl, was accomplished while maintaining binocular distance UCVA of 20/20 in 100% of patients at the 1-year follow-up examination. At the 3-year followup examination, 100% of patients maintained binocular distance UCVA of 20/20, with J3 or better near UCVA in 78% of patients. This decrease in near UCVA is due to progressive presbyopia and the small hyperopic shift observed during the 1-year and 3-year follow-up period. Despite this change in near UCVA, patients were still functioning well with near vision and were only using reading glasses 23% of the time for near tasks.

PREDICTABILITY AND STABILITY

Stability was evaluated as a mean diopter change in MRSE during the follow-up period. An overcorrection was initially observed following CK treatment. This overcorrection was reduced by early hyperopic regression. The rate of regression decreased after 3 months and stabilized 1 year after surgery, with 100% of eyes within ?0.75 D, 90% of eyes within ?0.50 D, and 60% of eyes within ?0.25 D of intended correction. Mean MRSE decreased by +0.25 D from 1 to 3 years, representing a change of 0.01 D per month. Three years postoperatively, 100% of eyes were within ?1.00 D, 78% were within ?0.75 D, 44% were within ?0.50 D, and 22% of eyes were within ?0.25 D of intended correction.

During the 3 years of follow-up, the mean MRSE of the dominant untreated eyes changed by +0.26 D. The +0.18-D change during the 2-year period in the untreated eyes was not significantly different than the change (+0.25 D) in the CK-treated eyes from the 1- to 3-year follow-up period. This finding demonstrates excellent refractive stability for the CK-treated eyes. The slight hyperopic shift that was seen in both the CKtreated and the untreated eyes is the natural hyperopic shift observed in this age group that has been reported in longitudinal population-based studies.910 In addition, there was no change in keratometry from 1 to 3 years, indicating no regression of the corneal power (steepening) following CK.

SAFETY

No intra- or postoperative complications occurred in this study. No eyes lost lines of BSCVA. No eyes had an increase in cylinder >0.75 D 3 years following surgery. Conductive keratoplasty for presbyopia continues to be a safe procedure 3 years following treatment.

SURGICAL TECHNIQUE

Patients in this study were treated using the original standard pressure CK technique. In this technique, uniform downward pressure that dimples the cornea is applied to ensure that the top of the probe is fully seated in the stroma, and this downward pressure is maintained during radiofrequency application.

The light touch CK technique has become popular with surgeons because of the greater refractive effect seen. Minimal to no compression (pressure) is applied to the cornea at the time of radiofrequency application with this technique. The greater refractive effect allows surgeons to eliminate treating at the 6-mm treatment zone, which results in less induction of astigmatism.11 In our experience, light touch CK is a more shallow treatment with greater regression than standard-pressure CK.

Most recently, the template-guided CK technique has been developed. A plastic, light-vacuum suction ring with predrilled holes is centered on the pupil. The template guides the accurate placement and depth of the keratoplast tip at select treatment zones. There is no corneal compression similar to light touch CK and the tip penetrates deep into the stroma similar to standard pressure CK. Template-guided CK removed the variables of the previous techniques by standardizing the technique to have more consistent centration of treatment, spot placement, application of pressure, and depth of treatment. Early results of template-guided CK appear better than that of standard-pressure and light touch techniques.12

TREATING PRESBYOPIA IN PLANO PRESBYOPES

There are no reports in the literature to compare the safety, efficacy, predictability, and stability of CK to photorefractive keratectomy (PRK) or LASIK performed in the nondominant eye for monovision treatment in piano presbyopic patients. The only previous presbyopia CK reports include the 6-month results from the CK presbyopia FDA clinical trial5 and the 1-year results from the same group of patients in this report.7

Because the amount of refractive change targeted with CK treatments for presbyopia is similar to CK treatments for mild to moderate hyperopia, a comparison of hyperopic CK to hyperopic LASIK and hyperopic PRK can be evaluated. Pallikaris et al8 reported 30-month results of CK for low to moderate hyperopia demonstrated better predictability than hyperopic PRK and similar predictability to hyperopic LASIK. They also found CK had more stable results than hyperopic PRK, hyperopic LASIK, and LTK.8 The safety reported with CK also was better compared to lines lost of BSCVA in PRK and LASIK studies.8

REFERENCES

1. Lans L. Experimentelle Untersuchungen ?ber die entstehung von astigmatismus durch nicht perforirende corneawunden. Graefes Arch Clin Exp Ophthalmol. 1898;45:117-152.

2. Seiler T, Matallana M, Bende T. Laser thermokeratoplasty by means of a pulsed holmium:YAG laser for hyperopic correction. Refract Corneal Surg. 1990;6:335-339.

3. Alio JL, Ismail MM, Sanchez Pego JL. Correction of hyperopia with non-contact Ho: Y AG laser thermal keratoplasty. / Refract Surg. 1997;13:17-22.

4. McDonald MB, Hersh PS, Manche EE, Maloney RK, Davidorf J, Sabry M, and the Conductive Keratoplasty United States Investigators Group. Conductive keratoplasty for the correction of low to moderate hyperopia: US clinical trial 1-year results on 355 eyes. Ophthalmology 2002;109:1978-89.

5. McDonald MB, Durrie DS, Asbell PA, Maloney R, Nichamin L. Treatment of presbyopia with conductive keratoplasty: sixmonth results of the United States FDA clinical trial. Cornea. 2004;23:661-668.

6. United States FDA PMA P010018: R?fract?e ViewPoint CK System. Physician's Reference Guide for Treatment of Presbyopic Emm?tropes and Hy per op es to Improve Near Vision Utilizing Conductive Keratoplasty (CK). Irvine, Calif: R?fract?e Ine; 2004.

7. Stahl JE. Conductive keratoplasty for presbyopia: 1-year results. J Refract Surg. 2006;22:137-144.

8. Pallikaris IG, Naoumidi TL, Astyrakakis NI. Long-term results of conductive keratoplasty for low to moderate hyperopia. / Cataract Refract Surg. 2005;31:1520-1529.

9. Gudmundsdottir E, Jonasson F, Jonsson V, Stefansson E, Sasaki H, Sasaki K, and the Iceland-Japan Co- Working Study Groups. "With the rule" astigmatism is not the rule in the elderly. Reykjavik Eye Study: a population based study of refraction and visual acuity in citizens of Reykjavik 50 years and older. Acta Ophthalmol Scand. 2000;78:642-646.

10. Gudmundsdottir E, Arnarsson A, Jonasson F. Five-year refractive changes in an adult population: Reykjavik Eye Study. Ophthalmology. 2005;112:672-677.

11. Milne HL. NearVision CK with LigiiiTouch? My personal technique and nomogram. ViewP oints. Winter 2005. Available at: http://www.refractec.com/viewpoints/archive. asp?article=05W3. Accessed January 8, 2007.

12. Stahl ED, Durrie DS. Temp late -guided conductive keratoplasty using the ViewPoint CK system for optimizing near vision. Presented at: American Society of Cataract and Refractive Surgery Annual Meeting; April 29, 2007; San Diego, Calif.

TABLE 1

Preoperative, Surgical, 1-year, and 3-year Postoperative Data on 10 Eyes Treated With Conductive Keratoplasty for Presbyopia

TABLE 1

Preoperative, Surgical, 1-year, and 3-year Postoperative Data on 10 Eyes Treated With Conductive Keratoplasty for Presbyopia

10.3928/1081-597X-20071101-07

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