Conductive keratoplasty to correct residual hyperopia after corneal surgery

Conductive keratoplasty to correct residual hyperopia after corneal surgery Ian F. Comaish, FRCOphth, Michael A. Lawless, FRACO, FRCOphth Conductive keratoplasty (CK) is an electrical-current-based technique for steepening the central cornea to reduce low to moderate hyperopia. We report 4 patients who had CK to correct hyperopia after laser in situ keratomileusis (LASIK) and were followed for at least 6 months. An overcorrection was noted after the CK procedure in all patients, but no sight-threatening complications arose. Conductive keratoplasty appears to be safe and well tolerated after LASIK. However, the algorithms should be modified to increase the predictability of the CK procedure in previously treated eyes. J Cataract Refract Surg 2003; 29:202–206 © 2003 ASCRS and ESCRS

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onductive keratoplasty (CK) (Refractec, Inc.) is a new, “laserless,” electrical-current-based (radiofrequency 350 kHz) technique for steepening the contours of the cornea to reduce hyperopia. The treatment is administered by the stainless steel Keratoplast tip (Figure 1) , 450 ␮m long and 90 ␮m wide, which is inserted into the midperipheral cornea at 8 to 32 treatment spots and releases radiofrequency energy deep into the stroma. Tissue resistance to current flow generates localized heat (65°C to 75°C) that denatures and shrinks peripheral corneal collagen in a controlled fashion (data on file, Refractec, Inc.). Each treated spot results in a cylindrical footprint, approximately 150 to 200 ␮m wide and 500 ␮m deep (approximately 80% of the corneal depth) (P. Goth, MD, R. Stern, MD, “Conductive Keratoplasty: Principles and Technology,” presented at the Symposium on Cataract, IOL and Refractive Surgery, Boston, Massachusetts, USA, April 2000). A circle of treatment spots causes a band of tightening that flattens the peripheral cornea and steepens the central cornea.

Figure 1. (Comaish) The Keratoplast tip (90 ␮m wide, 450 ␮m long) with a coated stop at the distal end shown next to a 7-0 suture.

Conductive keratoplasty has been shown to be effective, safe, and predictable in United States Food and Drug Administration phase III clinical trials in patients with untreated low to moderate hyperopia.1 We report the outcomes in 4 patients who had CK after corneal refractive surgery.

Accepted for publication March 7, 2002. From The Eye Institute, New South Wales, Australia. Dr. Lawless is a paid medical monitor of Refractec, Inc., for the international studies on conductive keratoplasty. Dr. Comaish has no financial interest in any product mentioned. Reprint requests to Michael A. Lawless, FRACO, FRCOphth, The Eye Institute, 270 Victoria Avenue, Chatsworth, New South Wales, 2067, Australia. E-mail: [email protected]. © 2003 ASCRS and ESCRS Published by Elsevier Science Inc.

Case Reports Case 1 A 53-year-old man with myopia had CK in the left eye 2 years after bilateral laser in situ keratomileusis (LASIK) to give him monovision; ie, mild myopia in 1 eye to aid reading and emmetropia in the other eye to aid distance vision. An 8-spot 0886-3350/03/$–see front matter doi:10.1016/S0886-3350(02)01498-0

CASE REPORTS: COMAISH

treatment was applied with a target of ⫺1.00 diopter (D), ie, ⫺1.60 D of effect. The spherical equivalent (SE) in the left eye changed from ⫹0.87 D before CK to ⫺1.50 D at 6 months (Table 1). The preoperative and postoperative topographies are shown in Figure 2.

Case 2 A 51-year-old myopic man had a rather thin ultrasonic central pachymetry reading (Corneo-Gage Plus 2, Sonogage, Inc.) preoperatively (Table 1) and was warned that an enhancement procedure would be unlikely if undercor-

Table 1. Summary of 4 cases. BCVA Case

Manifest Refraction

Pachymetry (␮m)

Distance

UCVA Near

Distance

Near

— —

CF CF

— —

N4.5 (J2) N4.5 (J2)

20/20⫺1 20/40⫺2

N18 (J13) N18 (J13)

1 Pre LASIK OD OS Post LASIK (12/12) OD OS Post-CK, OS only (8 spot) 3 mo 6 mo

⫺5.00 ⫺0.25 ⫻ 180 ⫺5.00 ⫺0.25 ⫻ 100

582 (US) 606 (US)

⫹0.75 ⫺0.50 ⫻ 35 ⫹1.25 ⫺0.75 ⫻ 115

542 (Orbscan) 540 (Orbscan)

20/20⫺1 20/25

⫺1.50 ⫺0.25 ⫻ 141 ⫺1.25 ⫺0.50 ⫻ 85

535 (Orbscan) 535 (Orbscan)

20/20 20/20

N5 (J3) N5 (J3)

20/60 20/60

N5 (J3) N5 (J3)

⫺6.50 ⫺2.75 ⫻ 44 ⫺6.75 ⫺0.50 ⫻ 85

496 (US) 502 (US)

20/25 20/25

— —

CF CF

— —

⫹3.00 ⫺1.25 ⫻ 35 ⫹3.00 ⫺0.75 ⫻ 145

365 (Orbscan) 392 (Orbscan)

20/20 20/25

— —

20/50 20/60

— —

⫺2.50 ⫺1.50 ⫻ 80 ⫺0.75 ⫺0.75 ⫻ 86

382 (Orbscan) 382 (Orbscan)

20/20 20/20

— —

20/80 20/40⫺2

N5 (J3) N5 (J3)

⫹0.25 ⫺1.50 ⫻ 66 ⫹1.00 ⫺1.00 ⫻ 61

365 (Orbscan) 365 (Orbscan)

20/20 20/20

— —

20/40⫺2 20/25

N5 (J3) N16 (J12)

⫺4.00 ⫺1.00 ⫻ 128 ⫺3.25 ⫺0.55 ⫻ 92

552 (US) —

20/20 20/40⫹2

— —

CF CF

— —

⫹0.75 ⫺0.25 ⫻ 24

507 (Orbscan)

20/20

—

⫺4.00 ⫺4.00 ⫻ 90 ⫺4.00 ⫺2.25 ⫻ 100 ⫺1.50 ⫺1.50 ⫻ 89 ⫺2.00 ⫺0.75 ⫻ 105

494 (Orbscan) 493 (Orbscan) 494 (Orbscan) –

20/30 20/25 20/20 20/25

— N5 (J3) N5 (J3) N5 (J3)

20/200 CF 20/60 –

— N5 (J3) N5 (J3) —

⫺8.75 ⫺0.50 ⫻ 12 ⫺9.00 ⫺1.00 ⫻ 180

514 (US) 507 (US)

20/30 20/30

— —

CF CF

— —

⫹1.50 ⫺0.50 ⫻ 120 ⫹0.25 ⫺0.75 ⫻ 5

441 (Orbscan) 423 (Orbscan)

20/25 20/20

— —

20/30 20/40

— —

⫺3.00 ⫺1.75 ⫻ 70 ⫺1.75 ⫺1.50 ⫻ 9 ⫺1.75 sphere

401 (Orbscan) 422 (Orbscan) 416 (Orbscan)

— 20/20 20/20

— N5 (J3) N5 (J3)

20/20 20/20

2 Pre LASIK OD OS Post LASIK (12/12) OD OS Post CK OS (24 spot) 1 wk 13 mo Post CK OD (8 spot) 1 mo 9 mo 3 Pre LASIK OD OS (amblyopic) Post LASIK OD 4/12 Post CK OD (16 spot) 1 wk 3 mo 12 mo 15 mo

6/12⫺2

—

4 Pre LASIK OD OS Post-LASIK (12/12) OD OS Post CK OD (8 spot) 1 wk 2 mo 6 mo

— 20/100 20/50⫺2

N5 (J3) N5 (J3) N5 (J3)

BCVA ⫽ best corrected visual acuity; UCVA ⫽ uncorrected visual acuity; US ⫽ ultrasound pachymetry with Corneo-Gage Plus 2; Orbscan ⫽ pachymetry with Orbscan II; CF ⫽ counting fingers

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Case 4 A 54-year-old woman had bilateral myopic LASIK (Table 1). The intended refraction was plano in the right eye and ⫺1.00 D in the left eye. The right eye was overcorrected. Two months after an 8-spot CK, the refraction in the right eye was ⫺1.75 –1.50 ⫻ 9. At 6 months, the astigmatism had regressed somewhat to ⫺1.75 D, with J3 uncorrected and 6/6 corrected visual acuity.

Discussion

Figure 2. (Comaish) Corneal topography of Case 1. Top: Before CK. Middle: One month after CK. Bottom: Nine months after CK.

rection with LASIK occurred. At 1 year, both eyes were overcorrected. A 24-spot CK was performed in the left eye, targeting ⫹2.50 D of effect. One week postoperatively, however, the patient was overcorrected, with a change of nearly ⫺6.00 D rather than the intended ⫺2.50 D. This situation persisted, and an 8-spot CK was planned in the right eye. At 9 months, the patient had ⫹1.00 D of hyperopia in the right eye. At 13 months, the hyperopia in the left eye had regressed somewhat.

Case 3 A 52-year-old woman with amblyopia in the left eye had myopic LASIK in the right eye (Table 1). Four months postoperatively, the cycloplegic refraction was ⫹0.75 – 0.25 ⫻ 24. A 16-spot CK was performed to achieve ⫹1.25 D of effect. At 1 month, she was overcorrected. Overall, the subjective SE changed from ⫹0.62 D before CK to ⫺5.12 D at 1 month and ⫺2.37 D at 15 months. 204

Modern thermal surgical procedures that have been used to treat previously untreated hyperopia include pulsed, noncontact holmium:YAG (Ho:YAG) laser thermal keratoplasty (LTK),2– 8 contact Ho:YAG LTK,9,10 diode LTK,11,12 and CK.13 Thermal techniques have also been used to treat residual hyperopia in eyes that have had photorefractive keratectomy (PRK)14,15 and LASIK.16 Conductive keratoplasty delivers radiofrequency energy directly into the corneal stroma to heat collagen locally at the treatment spots. A circle of treated spots shrinks the periphery and steepens the center. The spots are delivered manually in a sequence of paired opposing spots, in contrast to noncontact LTK, which delivers all the spots simultaneously. It is not known whether this manual method of delivery is as reproducible. Contraction of collagen in the presence of heat is a function of temperature and time and occurs in 2 phases.17,18 In the first phase, at approximately 56°C, collagen undergoes transition from a triple helix structure to a random coil and the human cornea begins to contract. In the second phase, at approximately 75°C, collagen is completely denatured and converted to a gel-like state. The temperature “window” for collagen contraction without complete denaturation under steady-state conditions is 65°C to 75°C.17–19 In contrast to the CK technique, the Ho:YAG beam of the Hyperion (Sunrise Technologies) noncontact LTK technique generates a cone-shaped collagen shrinkage zone (conical footprint),2,20 with corneal denaturation decreasing from top to bottom. Such a conical footprint could be expected to be associated with more shallow thermal penetration. Deep thermal penetration in the treatment zone is desirable for permanent collagen shrinkage,17 which is expected to reduce postoperative regression and provide predictable and stable results. Manufacturers assert that the footprint extends

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cornea leaves the central corneal thickness unchanged any more than one should assume that central LASIK or PRK leaves the periphery unchanged.21 Conductive keratoplasty appears to be an effective and safe procedure for steepening the central corneal curvature, but different algorithms for the amount of treatment may be necessary when the procedure is used after LASIK.

References

Figure 3. (Comaish) Porcine corneal histology demonstrating cylindrical footprint of CK.

to approximately 80% of the depth of the midperipheral cornea (Figure 3). Regression of effect and low predictability have hampered the otherwise successful outcomes of thermal keratoplasty for untreated low levels of hyperopia.5–7 Results are mixed when thermal keratoplasty is used to treat hyperopia after PRK14,15 and LASIK.16 Each of our 4 cases retained excellent corrected visual acuity after CK, but a notable overcorrection was sustained in every case. These patients had been overcorrected by LASIK for myopia and were therefore a highly select group that may have had conformational or physiological peculiarities of the cornea. This might have predisposed them to an unusually large response. However, it is also possible that LASIK itself altered their responsiveness to CK by thinning the central cornea or altering the structural relationships of the anterior and posterior lamellae. We did not adjust the CK treatment zone in view of the LASIK flap, and we centered the treatment on the geometrical center of the cornea. In Cases 3 and 4, there was some alteration noted in the central Orbscan威 (Bausch & Lomb) pachymetry before and after CK, which was unexpected since the central zone was not treated. (Orbscan pachymetry was not available in our center to assess these patients before LASIK.) This finding appeared to reverse somewhat with time. It is, of course, entirely possible that these changes were artifacts; for example, that the Orbscan triangulation was thrown off as a result of CK spots or due to continuing changes after LASIK. It should not be assumed, however, that any treatment of the peripheral

1. McDonald MB, Davidorf J, Maloney RK, et al. Conductive keratoplasty for the correction of low to moderate hyperopia: 1-year results on the first 54 eyes. Ophthalmology 2002; 109:637–649 2. Koch DD, Kohnen T, Anderson JA, et al. Histologic changes and wound healing response following 10-pulse noncontact holmium:YAG laser thermal keratoplasty. J Refract Surg 1996; 12:623–634 3. Koch DD, Kohnen T, McDonnell PJ, et al. Hyperopia correction by noncontact holmium:YAG laser thermokeratoplasty; United States phase IIA clinical study with a 1-year follow-up. Ophthalmology 1996; 103:1525– 1536; discussion by T Seiler, 1536 4. Koch DD, Abarca A, Villarreal R, et al. Hyperopia correction by noncontact holmium:YAG laser thermokeratoplasty; clinical study with two-year follow-up. Ophthalmology 1996; 103:731–740 5. Koch DD, Kohnen T, McDonnell PJ, et al. Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty; US phase IIA clinical study with 2-year follow-up. Ophthalmology 1997; 104:1938 –1947 6. Alio´ JL, Ismail MM, Sanche´z Pego JL. Correction of hyperopia with non-contact Ho:YAG laser thermal keratoplasty. J Refract Surg 1997; 13:17–22 7. Nano HD, Muzzin S. Noncontact holmium:YAG laser thermal keratoplasty for hyperopia. J Cataract Refract Surg 1998; 24:751–757 8. Durrie DS, Schumer DJ, Cavanaugh TB. Holmium: YAG laser thermokeratoplasty for hyperopia. J Refract Corneal Surg 1994; 10:S277–S280 9. Eggink CA, Bardak Y, Cuypers MHM, Deutman AF. Treatment of hyperopia with contact Ho:YAG laser thermal keratoplasty. J Refract Surg 1999; 15:16 –22 10. Eggink CA, Meurs P, Bardak Y, Deutman AF. Holmium laser thermal keratoplasty for hyperopia and astigmatism after photorefractive keratectomy. J Refract Surg 2000; 16:317–322 11. Bende T, Jean B, Oltrup T. Laser thermal keratoplasty using a continuous wave diode laser. J Refract Surg 1999; 15:154 –158 12. Geerling G, Koop N, Brinkmann R, et al. Continuouswave diode laser thermokeratoplasty in blind human eyes. J Cataract Refract Surg 1999; 25:32–40

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