Conductive keratoplasty (CK) is a nonablative, radiofrequency-based treatment;
this minimally-invasive treatment does not involve use of a laser. The treatment
is performed using the ViewPoint® CK System, and is based on the delivery of a
precise amount of radiofrequency energy through a probe tip inserted into the
peripheral corneal stroma in a ring pattern outside of the visual axis. The
peripheral application of the CK treatment creates a band of circumferential
tightening, resulting in a steepening of the central cornea to achieve the desired
refractive effect.
In April, 2002, the United States Food and Drug Administration granted
approval of the ViewPoint CK System (Refractec, Inc., Irvine, CA) for the treatment of mild to moderate (0.75 D to 3.00 D) previously untreated, spherical
hyperopia in persons 40 years old or older.1-3 This was followed by the
approval in March 2004 of using CK to improve near vision for presbyopic hyperopes or emmetropes through induction of a mild myopia in the non-dominant eye.4 Other potential uses of the CK treatment that some CK surgeons have explored include treatment of over- or undercorrections following LASIK or other excimer laser procedures, and the enhancement of outcomes following
cataract surgery and implantation of monofocal, multifocal, or accommodating
IOLs. CK has been very well received by surgeons, and more than 125,000 CK
treatments have been performed to date.
This paper will describe the early clinical trial results of CK used in patients who
have undergone a LASIK procedure for the treatment of myopia in the past and
now need improvement of near vision because of the onset of presbyopia.
PATIENTS AND METHODS
Patients enrolled in this FDA approval study are emmetropic presbyopes who
had LASIK treatment for 1.00 to 6.00 D of myopia at least 1 year earlier. Post-
LASIK, these patients must also have a manifest refractive spherical equivalent
(MRSE) of +0.50 D to -0.50 D, = 0.75 D of cylinder, residual central pachymetry of = 400 µm, and peripheral pachymetry of = 560 µm. They will all be treated with 1 ring of CK treatment (or 8 CK treatment spots) in the non-dominant eye for a 1.25 D add. A total of 150 post-LASIK presbyopic patients will be enrolled in the
study and followed for 1 year.
CLINICAL STUDY RESULTS
Objective Results: One month results are available on a total of 23 patients.
The mean age of this group was 51.5 years and they had a mean pre-LASIK
MRSE of -3.23 D. In the CK treated eye at 1 month, 91% have uncorrected
visual acuity (UCVA) at near of J2 or better and 96% have J3 or better, 78%
are at ± 0.50 D of target, and 91% have no clinically significant change in cylinder.
One patient had 1.00 D, and another one had >1.00 D of induced
cylinder post-CK. However, both of these patients had J1+ uncorrected near
VA. Uncorrected distance VA in the treated eye was 20/40 or better in 48%
and 20/63 or better in 87%. The mean refractive effect was 1.22 D ± 0.35. A
total of 83% had binocular UCVA-distance of 20/20. No patient lost 2 or
more lines of best spectacle corrected distance vision.
No adverse events, or LASIK flap complications occurred. A summary of key
results appears in Table 1.
Uncorrected Near VA
J1 or Better 87%
J2 or Better 91%
J3 or Better 96%
Binocular Uncorrected Distance VA
20/20 or Better 83%
20/25 or Better 100%
Predictability
± 0.50 D of Intended 78%
± 1.00 D of Intended 96%
Induced Cylinder
No Change 91%
1.00 D Change 4% (J1+)
> 1.00 D Change 4% (J1+)
1 Month
TABLE 1: KEY RESULTS 1 MONTH AFTER CK
SUBJECTIVE RESULTS
Patients rated their near vision and depth perception as good to excellent and reported little or no dependence on glasses for distance, near, and intermediate vision. Ninety-six percent (22 out of 23) of patients reported being satisfied or very satisfied with their vision post-CK. On a scale of +3 (significant improvement) to -3 (significant worsening), the patients mean score for level of visual improvement after NearVision CK was +2.7.
After the NearVision CK treatment, patients on average reported a slight decline from preoperative in their uncorrected distance vision, a marked increase in uncorrected near vision, and no change in depth perception. After the NearVision CK treatment, 83% of the patients reported being able to read newspaper-size print, compared with 22% who reported being able to do so before the treatment. Sixty-five percent were able to read small print after NearVision CK, compared with 4% before treatment.
Yet the patients still retained their distance vision, with no change from pre-CK to post-CK in ability to see street signs. After the NearVision CK treatment, patients on average reported no change in their dependence on glasses for distance vision (same as preoperatively), and a marked decrease in dependence on glasses for near and intermediate vision.
CONCLUSION
Post LASIK presbyopic patients treated with 1 ring of CK treatment at the 8 mm
optical zone showed a mean refractive effect of 1.22 D and improvement in
uncorrected near and intermediate vision. An excellent safety profile was seen in
those patients treated with NearVision CK who have previously had LASIK surgery: there was no significant loss of best spectacle corrected visual acuity, no adverse events or LASIK flap complications, further supporting CK’s exceptional safety profile. High subjective patient satisfaction ratings and assessment of improvement in near, intermediate and distance vision were reported by patients in the study. These interim results of this ongoing trial are encouraging. Previous studies have shown some loss of effect after the 1 month visit so the expanded clinical trial will use a slightly smaller 7.5 mm optical zone to increase the effect. Longer term data on a larger number of patients is needed to definitively determine the safety and efficacy of NearVision CK performed on emmetropic presbyopes who have previously had a LASIK procedure.
