CK: A One-Year Retrospective
What I've learned after performing more than 600 conductive keratoplasty procedures.
BY GLENN H. STRAUSS, M.D.

Immediately following FDA approval of conductive keratoplasty (CK) in April 2002, I was excited about the potential of this new, minimally invasive hyperopic procedure that might rescue my refractive practice from the doldrums. Sure enough, my first patients were excited about this nonlaser procedure that could decrease their dependence on glasses -- possibly including their reading glasses. An initial marketing push and PR focusing on the reduction of presbyopic symptoms generated a tremendous response.

	How CK Changes the Cornea
	The mechanical effects of CK appear to optimize the prolate curvature of the cornea. The band of circumferential tightening (which is centered about 3.5 mm from the center of the cornea, with a width ranging from 1.5 mm to 3.5 mm, depending on the number of treatment rings applied) creates four distinct zones on the cornea: The apical zone is elevated and slightly steepened. The mid-central cornea is markedly steepened. Initially, the change is often 1.5 to 1.8 times the amount of desired keratometric change, followed by gradual relaxation within a few days. The third zone (in which treatment actually takes place) shows a belt-like tightening effect, the result of circumferential and radial forces pulling against the limbus. The peripheral limbal zone is flattened as a result of being tethered to the limbus. These changes result in the patient having minimal refractive overcorrection initially. This causes a marked improvement in near vision, while minimizing any loss in distance acuity. To achieve the maximum benefit, the final result should include a small amount of induced myopia in one eye (not as much as would be necessary for a standard monovision type correction.) In our practice, the incidence of undercorrection has been about 4%. These cases seem unlikely to achieve further improvement with more surgery.

Over the course of the past year, I've treated more than 600 patients with CK. In fact, CK has become the most frequently performed refractive procedure in my practice. Paradoxically, it's also increased our LASIK volume, possibly because some patients who come in to investigate CK discover they're not ideal candidates; many end up electing to undergo LASIK instead.

As a result of this experience, my confidence in the procedure has grown and I've learned a tremendous amount about its nature, limitations, and value. Here, I'd like to share some of what I've discovered.

More Than a Refractive Procedure

One of the biggest lessons I've learned is that conductive keratoplasty doesn't simply correct hyperopia. In fact, overall, I've found the most powerful application of CK to be for the correction of presbyopic symptoms. In my CK patients, who average 56 years of age, using the procedure to induce a small amount of myopia in one eye and emmetropia in the other -- less than a 1-diopter difference between the eyes -- has caused marked improvements in reading acuity. As you can see from the data in the two tables to the right, this trend is out of proportion to the degree of induced myopia. It suggests that CK is accomplishing more than a refractive endpoint can explain.

Because this degree of myopia is much less than the amount of myopia that could cause a disturbing monovision effect, the term "blended vision" has been coined to describe this system to patients. Even failed monovision contact lens wearers are frequently highly satisfied with the results of "blended vision."

Not Your Typical Refractive Patients

The second lesson that I've learned is that CK patients are quite different from my LASIK patients. Specifically:

• They tend to be older (average age: 56).
• Their main complaint tends to be that they're tired of their reading glasses, not a refractive distance complaint.
• These patients are oriented towards functional improvement rather than seeking a specific vision endpoint such as 20/20.
• Unlike LASIK patients, who expect the doctor to work miracles without help from the patient, CK patients tend to be willing to participate in the process of obtaining good acuity. If properly educated, they see CK as an opportunity to overcome the effects of aging rather than a way to fix a disease or condition. They're willing to work with the limitations of this new tool, by adjusting reading distance and lighting to get the result they want.

Three other characteristics set these patients apart:

• They're usually new to eye specialists. Prior to CK, these patients simply purchased over-the-counter reading glasses and tolerated decreasing distance acuity.
• Unlike myopic patients, who often have learned to deal with contact lenses early in life, these patients are frequently unwilling to try contact lenses.
• CK patients are wary of complications, but they're willing to take the risk that the procedure might not work.

The Right Patients = the Best Outcomes

Rather than trying to expand its indications, my experience has also taught me that there's a definite advantage to focusing on patients who are ideally suited for the CK procedure. Based on our experience, we primarily offer CK to patients who:

• are 45 years of age and older
• are in the -0.5 to +2.00 diopter range
• have up to 1.00D of corneal astigmatism
• have good correctable binocular acuity and minimal lenticular cylinder
• show less than 2+ nuclear sclerotic changes.

Offering CK primarily to these patients has decreased my re-operation rate to 8%. It has also decreased the incidence of induced astigmatism to between 1.5% and 2%. (Patients undergoing re-operation for induced astigmatism can be improved in 80% of the cases.)

To further increase the likelihood of a good outcome, I use what we call the "loose lens test" to determine which of these patients are most likely to be satisfied with the results of CK. (For a complete description of this test, see "Weeding Out Poor Candidates," on the facing page.)

Coincidentally, it appears that LASIK patients and pseudophakes will be excellent candidates for CK. I've seen a growing number of presbyopic LASIK patients who are now enjoying good vision following CK.

Risks and Limitations

As with any new procedure, we're also exploring the limits and risks of CK. Observations I've made during the course of the past year include:

• Most surgeon-related problems will probably occur in the first 40 patients. For example, inducing up to 2.5 diopters of cylinder in 20% to 30% of the first group of patients is not unusual. This cylinder does tend to decrease with time but may need to be addressed within the first 6 to 9 weeks by additional treatment.
• Patients with extensive hyperopia (greater than 2 diopters) tend to obtain less than the usual benefit from the conductive keratoplasty procedure. My mother-in-law, who is a bilateral +3.00 hyperope and 72 years old, was one of my first cases. She received a 32-spot treatment in both eyes, and within 3 days was 20/25 at distance and J3 at near. This was an outstanding result, but if I had known then what I know now, I wouldn't have chosen her to be one of my first cases.
• This procedure is not indicated for patients who don't have good binocular acuity with good stereopsis.
• Although CK is a powerful tool for correction of astigmatism, I'm not yet convinced that it's going to become a primary astigmatic procedure. Accurate axis alignment and reproducibility continue to be challenges. Correcting more than 1.5 diopters of corneal astigmatism is currently more of an art than a science.
• CK doesn't seem to be useful for the correction of hyperopic shift in RK patients. Initially I thought this would be a possible application, but my experience has been discouraging.
• One important contraindication for this age group is the presence of significant nuclear cataractous changes. (Cortical cataracts seem to be less of an issue.) Following CK, two patients complained of symptoms relating to nuclear sclerotic cataracts, even though preoperatively they had been asymptomatic. It's possible that the slight spherical aberration induced by CK added to aberration caused by the cataract. However, both patients underwent successful cataract surgery and achieved good results, with no adjustment made in the IOL calculation.
• More study will be needed to determine long-term stability. Current data suggests that stability is good compared with other thermokeratoplasty procedures and H-LASIK; 3-year FDA data show a reported drift of +0.25 diopters per year. However, I prepare all my patients for the eventuality of change. Generally, I tell patients that they can expect 3 to 4 years of effectiveness.

Off To a Great Start

My one-year post-op patients are now starting to present for follow-up. They report general satisfaction with their vision and continue to refer other patients for treatment.

Conductive keratoplasty has been a valuable addition to my refractive practice. I've found it rewarding to work with these patients and I anticipate long-term relationships with many of them, since this procedure requires upgrades after several years. Word of mouth has been strong, but marketing the key concepts has also been an important factor in generating volume.

After one year, CK has come into its own in my refractive practice. I look forward to what it will teach me over the next year.

Dr. Glenn Strauss is a board certified ophthalmologist specializing in cataract surgery, LASIK vision correction, and CK. He has been a principal investigator in research involving the healing process in refractive surgery, and was the first ophthalmologist in the state of Texas to perform the conductive keratoplasty procedure.