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CONDUCTIVE keratoplasty (ViewPoint™ Refractec® Inc) is a very safe, effective, and predictable technique for treating presbyopia in emmetropes and patients with hyperopia, report British researchers. Speaking at the XXI Congress of the European Society of Cataract and Refractive Surgeons, David Allamby MD presented results for a series of 104 eyes of 63 patients treated with CK in a ‘Blended Vision' approach to improve near vision. Three months after undergoing the CK procedure, 85% of patients were able to see 20/20 or better at both distance and near (N5) and all achieved UCVA of 20/25 at distance and could read N8 at near. Safety was excellent, with no infections, loss of BCVA exceeding one line, or development of any other significant complications. "CK has received FDA approval for the treatment of low to moderate hyperopia in eyes with no more than 0.75 D of cylinder, but it has potential application for other indications, including the treatment of presbyopia. In fact, most patients who have CK come in complaining about difficulty with reading, and currently, 80% of my patients treated with CK are presbyopes wanting improved near vision," Dr. Allamby said.
He noted that the idea of a laser-less procedure makes CK particularly appealing to the generally conservative group of 50- to 65-year-olds, and the demographic characteristics of his CK population are consistent with that observation. The 63 patients in his series had a mean age of 56 years with a range between 41 and 72. Men comprised 60% of the population. That gender distribution is the reverse of that found among patients who have laser vision correction surgery. The 104 eyes in the series included 59 eyes treated for distance correction and 45 to improve near vision. Preoperatively, mean MSE was +1.45 D (range 0.50 to +3.25 D) for the distance eyes and +0.67 D (range -0.50 to +1.75 D) for the near eyes. The serial refractive and visual outcomes demonstrate that CK results in an initial immediate overcorrection that resolves over time to reach the target between one and three, depending on the number of treatment spots placed. Mean SE decreased from +1.11 D preoperatively to -0.30 D on the first day after CK. After one week, SE regressed to -0.06 D, changing to -0.02 D and +0.05 D at one and three months, respectively. At one week, about three-fourths of eyes were within one dioptre of target SE and 60% were within 0.5 D. After one month, those values improved to 90% and 70%, respectively. Dr. Allamby observed that CK may also induce a minor amount of refractive astigmatism that tends to regress, although some eyes have one or two additional spots placed after one month to correct astigmatism. In his series, mean astigmatism increased from 0.32 D preoperatively to 1.30 D at one day and decreased to 1.08 D at one week. Consistent with the refractive changes over time, uncorrected acuities also improved progressively. Some 50% of patients had binocular UCVA of 20/20 or better preoperatively and 88% could see 20/40 or better. One week after CK, 52% of patients had binocular distance UCVA of 20/16 or better and 84% were seeing 20/20 or better. By three months, 100% had binocular distance acuity of 20/20 or better and 73% achieved 20/16 or better.
The data for binocular near acuity showed no patient was able to read N5 (20/20) preoperatively, and only 6% could read N8. At one week and three months, some 85% were reading N5 print and 100% could read N8. "One of the salient points about CK is that the desired effect is not entirely reached by the end of the first week or first month. Patients will notice their distance vision continues to improve month after month and even throughout the first year. However, most patients who have this procedure don't come in complaining about their distance vision. The improved reading vision is the real difference these patients appreciate and the gain in distance is something of a bonus for them," Dr. Allamby said.
Real-time imaging using very high frequency (VHF) Artemis 2 anterior segment ultrasonography provides a clear depiction of the unique corneal changes associated with conductive keratoplasty (CK), said Dr Allamby. He presented a series of ultrasound images taken at two months post-CK that demonstrated centration of the treatment around the visual axis, the desired change in corneal curvature with central steepening and peripheral flattening, and the deep and cylindrical nature of the lesions. An image of adjacent CK lesions allowed visualisation of a double-puncture through Bowman's membrane, with one break atop each cylindrical lesion. Also visible were increased areas of echogenicity between the lesions, a result of disorganisation of the collagen fibres induced by thermal shrinkage, as they descended to a depth of 80% to 90% of the stromal thickness. "The characteristic depth and geometry of the CK lesions distinguish CK from LTK (laser thermal keratoplasty) and are expected to translate into a more durable treatment effect," Dr. Allamby said. He explained that the tension lines produced between the circumferential, cylindrical CK lesions run parallel to the corneal surface, whereas the more superficial, conical footprint of LTK generates oblique tension. Typically, therefore, LTK is associated with a "sweet spot" for refractive correction at three months. Before that time, patients are relatively unhappy because of their overcorrection as well, and they become dissatisfied again thereafter as their vision degrades as the treatment effect rapidly regresses. "In contrast, the refractive stability pattern for CK much more closely matches that of laser vision correction for hyperopia," Dr. Allamby said. The VHF ultrasound images also showed the presence of a "safety zone" separating the posterior portion of the CK lesions from the anterior endothelial surface. "Endothelial cell counts have been documented to remain unchanged after CK, and those data are consistent with the ultrasound images showing the CK lesions end clear of the endothelial interface," he said.
David Allamby FRCS
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