Conductive Keratoplasty Research Articles

Conductive Keratoplasty to Treat Complications of LASIK and Photorefractive Keratectomy

Conductive Keratoplasty to Treat Complications of LASIK and Photorefractive Keratectomy

Conductive Keratoplasty: Histological Study of Human Corneas

To determine the morphologic changes in human corneas over time following radiofrequency-based conductive keratoplasty (CK) treatment. Prospective, observational case series. In a single-center study six human corneas of six patients with localized peripheral keratoconus underwent CK treatment followed by penetrating keratoplasty. Three spots were applied in the periphery of each cornea (6 mm optical zone). Corneal buttons were examined with light and electron microscopy at different postoperative intervals up to 6 months post-CK. In samples assessed on day one post-CK, small areas of detachment between the basal layer of epithelial cells and Bowman's layer were observed. At 1 week after the CK procedure, the epithelium appeared almost normal. Endothelium and Descemet's membrane had no alterations. In all samples, thermally induced misconfiguration of collagen fibers, described as "crumpled" changes of collagen layers, was observed reaching 75% to 80% of the stromal depth. The area of alterations had a cylindrical shape with a diameter of 120 mum. The conductive keratoplasty procedure produced collagen "crumpling and splitting" changes in human corneas, which were observed during the follow-up of 6 months. Areas adjacent to treatment site were minimally damaged.

Conductive Keratoplasty for the Correction of Residual Hyperopia After LASIK

To report the 6-month results concerning efficacy, safety, predictability, and stability of conductive keratoplasty for the correction of residual hyperopia after corneal refractive surgery. A total of 35 eyes (26 patients) with residual hyperopia after corneal refractive surgery ranging between +1.00 to +4.75 diopters (D) of spherical equivalent refraction were enrolled in the study and underwent conductive keratoplasty following a modified nomogram. Variables and data were available for all eyes at 6 months postoperatively. A total of 24 (69%) eyes had uncorrected visual acuity (UCVA) of > or = 20/40, and 10 (29%) eyes had UCVA of 20/20. Manifest refractive spherical equivalent was within +/- 0.50 D in 17 (49%) eyes and within +/- 1.00 D in 25 (71%) eyes in cases of previous hyperopic LASIK; the optical zone was significantly increased. Using a modified nomogram, conductive keratoplasty for correction of residual hyperopia was effective, but predictability was not satisfactory and safety needs to be established.

Conductive Keratoplasty to Treat Complications of LASIK and Photorefractive Keratectomy

To assess the outcomes of conductive keratoplasty (CK) for patients with complications related to LASIK or photorefractive keratectomy (PRK). Retrospective, noncomparative, interventional case series. Sixteen eyes of 15 patients were treated using CK after complications of initial LASIK or PRK surgeries. Five cases are described in detail. Rehabilitative CK was performed. Uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA), refractive error, keratometry, topography analysis, and a subjective assessment of visual quality. After CK treatment, there was a mean improvement in UCVA of 2 lines; 1 eye lost >1 line of UCVA. Best-corrected visual acuity improved or remained the same in 12 of 15 eyes; no eyes lost >1 line of BSCVA. There was a mean reduction in astigmatism of 54%. Videokeratography generally demonstrated improved quality of the corneal optical surface, and patients reported a reduction in optical symptoms such as glare and halo. Conductive keratoplasty may give improved corneal optics and vision in patients with complications of LASIK or PRK. This application of CK offers an alternative in cases in which further flap manipulation or laser treatments are contraindicated.

Long-term results of conductive keratoplasty for low to moderate hyperopia

To assess the long-term safety, efficacy, predictability, and stability of conductive keratoplasty (CK) for the treatment of low to moderate hyperopia and to evaluate the impact of the procedure on the quality of vision. University of Crete, Medical School, Vardinoyannion Eye Institute of Crete, Crete, Greece. In this prospective nonrandomized noncontrolled single-center study, 38 eyes of 26 patients (13 women and 13 men) were treated for hyperopia with a Refractec ViewPoint CK system and followed for 30 months. Preoperatively, the mean manifest refraction spherical equivalent (MRSE) was +1.89 diopters (D) +/- 0.6 (SD) (range +1.00 to +3.25 D), and the mean follow-up was 30.9 +/- 1.1 months. All eyes were treated with the regular CK nomogram for the treatment of spherical hyperopia. The treatment consisted of 8 to 32 spots applied to the periphery of the cornea. Mean age was 50.3 +/- 8.8 years (range 31 to 71 years). All treated eyes were analyzed for safety, efficacy, predictability, and stability. At 12 months, the MRSE was -0.06 +/- 0.8 D and at 30 months was -0.02 +/- 0.7 D. At 30 months, the mean MRSE was within +/-0.50 D in 68%, within +/-1.00 D in 92%, and within +/-2.00 D in all eyes. At 30 months, uncorrected visual acuity was 20/20 or better in 52.5% and 20/40 or better in 89% of eyes. No eye lost 2 or more Snellen lines or had an induced cylinder of 2.00 D or greater. The procedure did not cause statistically significant changes in contrast sensitivity. Results show that CK for low to moderate hyperopia is a safe, effective, predictable, and stable procedure.

Anterior chamber inflammation induced by conductive keratoplasty

Anterior chamber inflammation induced by conductive keratoplasty

Conductive Keratoplasty and the Coupling Phenomenon

To determine whether changes in corneal astigmatism with astigmatic conductive keratoplasty (CK) treatment obey Gaussian coupling (i.e., the steepening of the flat axis associated with the flattening of the steep axis) and to measure the coupling ratio and the coupling constant to determine the effect of astigmatic CK treatment on spherical equivalent. Retrospective review of 33 eyes in 24 patients who had undergone CK for hyperopia and who were treated intraoperatively for induced astigmatism. Induced astigmatism was determined by comparison of keratometric readings before and after CK. The coupling ratio was calculated according to two equations: clinical coupling ratio (1.61 +/- 0.81 diopters) and coupling ratio of the surgically induced refractive change (1.57 +/- 1.16 diopters). Values of the coupling ratio between 0.72 and 1.88 indicate coupling. The cornea does not behave according to Gauss's law of elastic domes. The targeted flat axis and steep axis 90 degrees away are affected by CK in opposite but not equal amounts. Therefore, when correcting surgically induced astigmatism with CK, the overall spherical equivalent of the patient will change because the coupling ratio is not equal to 1.

Intraocular Pressure Measurements After Conductive Keratoplasty

To determine the possible impact of conductive keratoplasty (CK) on intraocular pressure (IOP) measurements. A prospective, single-center, noncomparative interventional case series was performed. Baseline and postoperative IOPs were measured by Goldmann applanation tonometry in 32 eyes of 18 patients who underwent CK for hyperopia correction. Mean follow-up was 11.9 months (range: 8 to 18 months). After CK, a statistically significant decrease in the measured IOP was observed (before CK: 14.22+/-1.64 vs after CK: 12.66+/-2.21, P<.001). The change in IOP readings postoperatively was not correlated with age, sex, keratometric readings, or attempted correction. Despite the limitations due to the small number of patients enrolled in this study, the applanation tonometer appears to underestimate the true IOP after CK.

Intraoperative Correction of Induced Astigmatism After Spherical Correction of Hyperopia With Conductive Keratoplasty

To evaluate the treatment of surgically induced astigmatism intraoperatively during conductive keratoplasty (CK) for correcting hyperopia. Conductive keratoplasty uses radiofrequency energy applied to the peripheral corneal stroma to shrink the collagen and alter the central cornea to correct hyperopia. Nineteen consecutive patients (27 eyes) who underwent CK for hyperopia and were treated intraoperatively for induced astigmatism were examined. By using automated keratometric readings taken during the procedure, additional spots were applied at the minus cylinder or flat axis at the 7-mm zone until the intraoperative astigmatism was 2 diopters (D) or less. The intraoperative treatment reduced the astigmatism by an average of 2.30 +/- 1.32 D (P=0.00001). The mean induced astigmatism was 3.33 +/- 0.14 D for eyes that received eight spots, 4.12 +/- 1.13 D for eyes that received 16 spots, 4.43 +/- 0.82 D for eyes that received 24 spots, and 4.60 +/- 1.08 D for eyes that received 32 spots. Additional spots reduced astigmatism in most patients to less than 2 D. Intraoperative treatment of astigmatism through the addition of more spots at the minus cylinder or flat axis reduced the degree of induced astigmatism. Surgically induced astigmatism was observed more frequently in patients who received 32 treatment spots and 6-mm treatment zone application.

Modeling for radio-frequency conductive keratoplasty: implications for the maximum temperature reached in the cornea

Conductive keratoplasty (CK) is a new surgical technique for steepening the contours of the cornea to reduce hyperopia. It has been emphasized that during CK, tissue resistance to radio-frequency electrical current flow generates a localized heat with temperatures between 65 and 75 °C; however, we hypothesize that the maximum temperature reached in the cornea may be higher. For this reason, we developed a finite-element model to estimate the temperature distributions in the cornea during CK. The time evolution of the impedance obtained from computer simulations was compared to that obtained in an experimental study previously published. Our results show that during a typical CK with a 60% setting power (equivalent to 200 V peak-to-peak), the cornea may reach temperatures over 100 °C at the electrode tip. On the other hand, the initial impedance of the cornea has a significant influence on the temperature distribution, while the initial temperature of the cornea is not a significant parameter. The results also suggest that low power settings (30–40%) do not produce temperatures over 100 °C. Finally, although the actual voltage waveform during CK is exponential and pulsed, our model based on a constant voltage (with a value equal to the root mean square value) provides a better agreement between the theoretical impedance time evolution and that obtained experimentally.

Corneal modeling of keratoconus by conductive keratoplasty

We evaluated the effect of conductive keratoplasty (CK) applications for corneal modeling to treat keratoconus or post-laser in situ keratomileusis (LASIK) corneal ectasia in 3 patients. Treating keratoconus with CK applications resulted in more regular topography with visual improvement.

US Trends in Refractive Surgery: 2003 ISRS/AAO Survey

ABSTRACT PURPOSE: To determine the latest trends in refractive surgery in the United States. METHODS: All US members of the International Society of Refractive Surgery of the American Academy of Ophthalmology were mailed the 2003 refractive surgery survey dealing with volumes, types, preferences of refractive surgery performed, and use of new emerging technology. Questions regarding radial keratotomy (RK), astigmatic keratotomy (AK), limbal relaxing incisions (LRI), photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), laser subepithelial keratomileusis (LASEK), intracorneal ring segments (ICRS), laser thermokeratoplasty (LTK), conductive keratoplasty (CK), phakic intraocular lenses (PIOL), clear lens extractions (CLE), and scleral expansion (SE) procedures were examined in the survey. Use of lasers, microkeratomes, pupillometry instruments, postoperative medications, wavefront analyzers, topographers, etc were examined. RESULTS: In 2003, LASIK continued to dominate for refractive errors between -8.00 to +3 diopters. Surgeons are waiting on the PIOL for high myopes and are performing CLE for high hype ropes. Photorefractive keratectomy, LASIK, LASEK, CLE, PIOL, and CK appeared to have bright futures; whereas, RK, ICR, LTK and SE were on the decline. Bilateral LASIK at the same surgical session is offered by 98% of surgeons. VISX lasers are used 2:1 over all other lasers in the United States. Zeiss- Humph rey still dominates topographers at 37%. The Bausch &amp; Lomb Hansatome (48%) leads microkeratomes. Surgeons are charging, on average, $300-$500 more per eye for custom ablations and these ablations have already been accepted and integrated into refractive practices. Comanaging of refractive surgery patients is significantly down from previous years. Fourth -gene ration fluoroquinolones overtook the postoperative antibiotic prescriptions, with prednisolone and fluoromethalone dominating as anti-inflammatories. CONCLUSIONS: Trends and changes as refractive surgery grows in the mainstream of ophthalmology in the United States continue to be elucidated by this professional organization survey. [J Refract Surg. 2005;21:87-91.]

Conductive keratoplasty

Less-invasive surgical techniques are being preferred in the treatment of eye conditions such as myopia, hyperopia, and presbyopia. This paper discusses clinical studies of a technique that falls on this category called conductive keratoplasty (CK). The goal of the CK procedure is to produce minor corneal surface changes that result in a decreased local radius of curvature. This procedure uses radiofrequency currents in reshaping the cornea. The patients with hyperopia could, most of the time, notice near vision improvements immediately after the procedure. In most patients, far vision was not significantly affected. Presbyopes also noticed a significant improvement in near vision. Of over 100 patients enrolled in the clinical trial, 98% could see J5 (magazine- and newspaper-sized print) in the eye that was treated. Additionally, 87% of patients could see 20/20 in the distance and also read J3 or phonebook-sized print (significantly smaller than news print). As these results point to a promising future for CK, the procedure is being adopted by an increasing number of opthalmic surgery centers.

Laser in situ keratomileusis after conductive keratoplasty

We present a patient in whom laser in situ keratomileusis was used to treat residual hyperopia with astigmatism after conductive keratoplasty (CK). Previous CK did not affect initial flap creation, the ability to lift the flap manually 3 weeks after its initial preparation, or the refraction, topography, and refractive stability after the flap was created.

Conductive keratoplasty.

Conductive keratoplasty.

Corneal perforation after conductive keratoplasty with previous refractive surgery

A 56-year-old woman had conductive keratoplasty (CK) for residual hyperopia and astigmatism. Three years before the procedure, the patient had arcuate keratotomy, followed by laser in situ keratomileusis 2 years later for high astigmatism correction in both eyes. During CK, a corneal perforation occurred in the right eye; during the postoperative examination, an iris perforation and anterior subcapsule opacification were seen beneath the perforation site. The perforation was managed with a bandage contact lens and an antibiotic–steroid ointment; it had a negative Seidel sign by the third day. The surgery in the left eye was uneventful. Three months after the procedure, the uncorrected visual acuity was 20/32 and the best corrected visual acuity 20/20 in both eyes with a significant improvement in corneal topography. Care must be taken to prevent CK-treated spots from coinciding with areas in the corneal stroma that might have been altered by previous refractive procedures.

Two-year results of conductive keratoplasty for the correction of low to moderate hyperopia

Purpose: To evaluate the 2-year postoperative safety, efficacy, predictability, and stability results of conductive keratoplasty (CK) to correct low to moderate hyperopia. Setting: Department of Ophthalmology, Stanford University Medical Center, Stanford, California, USA. Methods: In a prospective nonrandomized noncontrolled trial, 25 eyes of 14 patients with +0.75 to +3.00 diopters (D) of hyperopia and ≤0.75 D of cylinder were treated with CK. Low-energy, radio-frequency current was applied to the peripheral corneal stroma through a probe inserted at 8 to 32 treatment spots. An early nomogram was used in 2 eyes, and a current nomogram was used in 23 eyes; the intended refraction was plano. The 23 eyes treated with the current nomogram were analyzed for efficacy, predictability, and stability. All 25 eyes were included in the safety and patient-satisfaction analyses. Results: Preoperatively, the mean manifest refraction spherical equivalent (MRSE) in the 23 current-nomogram eyes was +1.55 D. At 2 years, the uncorrected visual acuity was 20/20 or better in 64% of eyes and 20/40 or better in 95%. The MRSE was within ±0.50 D in 64% of eyes, within ±1.00 D in 91%, and within ±2.00 D in 100%. No eye lost more than 1 line of best spectacle-corrected visual acuity or had an induced cylinder greater than 0.75 D. The mean MRSE of the cohort with all follow-ups was +0.48 D, which reflected a 29% regression from the intended plano and 43% regression from the 1-month postoperative overcorrection. The rate of regression appeared to be low and decreasing, +0.024 D per month between 12 and 24 months. A patient survey revealed improved quality of vision and a high level of satisfaction. Conclusions: Conductive keratoplasty appeared to be safe, effective, and predictable for correcting low to moderate hyperopia. Mild hyperopic regression was observed; however, the rate of regression indicated by the mean change in MRSE per month was low and decreased over the 2-year follow-up. Longer follow-up may be necessary to further characterize the refractive stability of CK.

Zernike polynomial fitting fails to represent all visually significant corneal aberrations.

It is assumed that wavefront error data arising from aberrometry are adequately described by a Zernike polynomial function, although this assumption has not been extensively tested. Inaccuracies in wavefront error may compromise clinical testing and refractive correction procedures. The current retrospective study correlates visual acuity with corneal wavefront error and with the residual surface elevation error after fitting with the Zernike method. Corneal topography maps were obtained from 32 keratoconus cases, 27 postoperative penetrating keratoplasty cases, and 29 postoperative conductive keratoplasty cases (88 total). The best spectacle-corrected visual acuity (BSCVA) for each case ranged from -0.2 to 1.3 logarithm of the minimum angle of resolution (logMAR) units (20/12.5-20/400). Topography was analyzed to determine wavefront error and the elevation fit error for a 4-mm optical zone. The 4th and 10th expansion series were analyzed with the 0th-order (piston) and 1st order (tip and tilt) removed. Linear regression analysis was performed. The difference in root mean square (RMS) error between the 4th- and 10th-order analyses was assessed for both wavefront and elevation fit error. The correlation of BSCVA to wavefront error for 4th-order terms was moderately strong and significant (R2=0.581; P<0.001). The 10th-order correlation for wavefront error had a similar result (R2=0.565; P<0.001), but the regression was not significantly different from the 4th-order result. The correlation of BSCVA to the elevation fit error was strong and significant for the 4th order (R2=0.658; P<0.001). The 10th-order data had a similar result (R2=0.509; P<0.001), and there was no significant difference between the two regressions. Only 72% of the cases showed a shift toward increased wavefront error with the 10th-order series, whereas 18% lost wavefront error. All cases showed a shift toward improved elevation fit with the 10th-order expansion. The wavefront error correlation to acuity was moderately strong, but the corneal elevation fit error also strongly correlated with visual acuity, indicating that Zernike polynomials do not fully characterize the surface shape features that influence vision and that exist in postsurgical or pathologic eyes. In addition, the change in wavefront error when using a larger expansion series was found to increase or diminish somewhat unpredictably. The authors conclude that Zernike polynomials fail to model all the information that influences visual acuity, which may confound clinical diagnosis and treatment.

Update on nonexcimer laser refractive surgery technique: conductive keratoplasty.

Excimer laser-based refractive surgery techniques have been the most popular forms to correct myopia, hyperopia, and astigmatism. However, development of non-excimer based refractive surgery such as thermal techniques provides a viable alternative to laser vision correction. Earlier forms of thermal techniques showed a lack of predictability and stability, resulting in the abandonment of the further development of these techniques. Recently, conductive keratoplasty, a laserless, radiofrequency-based technique, has been approved by the FDA for the correction of low to moderate hyperopia. Preliminary data showed that conductive keratoplasty seems to be safe, effective, and showed good refractive stability. This review will discuss recent studies on conductive keratoplasty technique in terms of its efficacy, safety, refractive predictability, and stability.

Corneal iron ring after conductive keratoplasty

Purpose To report formation of corneal iron ring deposits after conductive keratoplasty. Design Observational case report. Methods Case report. Results A 54-year-old woman underwent conductive keratoplasty for hyperopia. One year after conductive keratoplasty, iron ring pattern pigmentation was detected at the corneal epithelium of both eyes. Conclusions This is the first report of the appearance of corneal iron ring deposits following conductive keratoplasty treatment in a patient. It is suggested that alterations in tear film stability, resulting from conductive keratoplasty-induced changes in corneal curvature, constitute the contributory factor for these deposits.