Conductive keratoplasty for the correction of low to moderate hyperopia: U.S. clinical trial 1-year results on 355 eyes

Advances in Corneal Surgical and Pharmacological Approaches to the Treatment of Presbyopia

The purpose of this article is to review the current status of presbyopia amelioration with surgical and pharmacologic procedures that partially compensate for loss of accommodation in advance of cataract surgery and lens replacement. Over the last few years, several corneal surgical and topical pharmacological approaches for the treatment of presbyopia have been introduced to the marketplace or are in the developmental pipeline. The approaches vary in invasiveness, duration of effect, reversibility, risk/benefit ratio, and clinical results. The advantages and disadvantages for each are discussed. Corneal surgical interventions aim to provide improved near and intermediate vision in patients with presbyopia through refractive means that extend ocular depth of focus through shape modification. The use of miotic drops or corneal lamellar implants extend depth of focus with the "pinhole" aperture size reduction effect. Unlike in adults younger than 40 years, the refractive status of the patient with presbyopia is not stable. Hence, procedures that provide a permanent refractive change may not provide long-term full correction; eye drops or other treatments that are self-reversing in time or are easily reversible may be used as needed. On the horizon, procedures are being explored that may add years of functional lens accommodation by preserving the deformable gel properties of the lens. [J Refract Surg. 2021;37(6 Suppl):S20-S27.].

Posterior Capsule Opacification With Two Hydrophobic Acrylic Intraocular Lenses: 3-Year Results of a Randomized Trial

PURPOSE

To compare the incidence and intensity of posterior capsule opacification (PCO) and neodymium-yttrium-aluminum-garnet (Nd:YAG) capsulotomy rates between 2 similar open-loop single-piece hydrophobic acrylic intraocular lenses (IOLs) that differ in the proprietary material characteristics and design features, over a period of 3 years.

DESIGN

Randomized, prospective, patient- and examiner-masked clinical trial with intraindividual comparison.

METHODS

Setting: Department of Ophthalmology, Medical University of Vienna, Vienna, Austria.

PATIENT POPULATION

Eighty patients (160 eyes) had bilateral cataract surgery and received a Vivinex XY1 IOL in 1 eye and an AcrySof SN60WF IOL in the other eye.

OBSERVATION PROCEDURES

Follow-up examinations were performed 3 years after surgery. Digital retroillumination images were taken of each eye. The amount of PCO (score: 0-10) was assessed subjectively at the slit lamp and objectively using automated image analysis software (AQUA).

MAIN OUTCOME MEASURE

PCO score (scale, 0-10).

RESULTS

The mean objective PCO score of the Vivinex XY1 IOLs was 0.9 ± 0.8 compared to the PCO score of 1.4 ± 1.1 for the AcrySof SN60WF IOLs (P < .001). Three years postoperatively, 11.4% of patients had an Nd:YAG capsulotomy in the Vivinex XY1 eye and 18.6% had a capsulotomy in the AcrySof SN60WF eye (P = .23).

CONCLUSION

The new hydrophobic acrylic Vivinex XY1 IOL showed significantly lower PCO rates and lower YAG rates compared to the AcrySof SN60WF IOL. The interaction of various factors such as hydrophobic material, smooth optic surface, and sharp posterior optic edge plays a key role in PCO development.

Microwave treatment of the cornea leads to localised disruption of the extracellular matrix

Microwave keratoplasty is a thermo-refractive surgical procedure that can correct myopia (short-sightedness) and pathologic corneal steepening by using microwave energy to cause localised shrinkage around an annulus of the cornea leading to its flattening and vision correction. The effects on the corneal extracellular matrix, however, have not yet been evaluated, thus the current study to assess post-procedure ultrastructural changes in an in-vivo rabbit model. To achieve this a series of small-angle x-ray scattering (SAXS) experiments were carried out across whole transects of treated and untreated rabbit corneas at 0.25 mm intervals, which indicated no significant change in collagen intra-fibrillar parameters (i.e. collagen fibril diameter or axial D-period), whereas inter-fibrillar measures (i.e. fibril spacing and the degree of spatial order) were markedly altered in microwave-treated regions of the cornea. These structural matrix alterations in microwave-treated corneas have predicted implications for corneal biomechanical strength and tissue transparency, and, we contend, potentially render microwave-treated corneas resistant to surgical stabilization using corneal cross-linking procedures currently employed to combat refractive error caused by corneal steepening.

360-Degree Iris Burns Following Conductive Keratoplasty

PURPOSE

The authors report a case with multiple iris burns after conductive keratoplasty to correct hyperopia.

METHODS

Case report.

RESULTS

A 52-year-old woman with hyperopia had a previous conductive keratoplasty procedure and underwent a conductive keratoplasty re-treatment 6 months later. Postoperatively, she presented with 360-degree iris burns in both eyes that were correlated with the corneal conductive keratoplasty scars. In addition, specular microscopy revealed decreased endothelial cell density for both eyes.

CONCLUSIONS

This is the first reported case of iris burns associated with conductive keratoplasty. [J Refract Surg. 2016;32(11):776-778.].

Optimal Keratoplasty for the Correction of Presbyopia and Hypermetropia

Purpose. To evaluate prospectively the safety and efficacy of optimal keratoplasty for the correction of hyperopia and presbyopia. Methods. Consecutive patients undergoing bilateral optimal keratoplasty for refractive presbyopic and hypermetropic corrections were enrolled. Each patient received a complete ophthalmologic examination at baseline, 1 hour, 1 day, 1 week, 1 month, 3 months, and 6 months after treatment. Results. The study included 40 consecutive eyes of 20 patients. All patients reached the 6-month follow-up. No serious intra- or postoperative complications were recorded. Monocular and binocular uncorrected near visual acuities improved significantly during the follow-up (p < 0.001). Binocular uncorrected distance visual acuity in presbyopic patients improved from 0.28 logMAR to a maximum of 0.04 logMAR (from 20/38 to 20/22 Snellen equivalent) the day after the treatment and remained significantly better than baseline until the end of the follow-up. A significant improvement of patient satisfaction for near (p < 0.001) and distance (p = 0.007) activities was seen the day after treatment and was maintained throughout the follow-up. Conclusions. Optimal keratoplasty is a safe, noninvasive, rapid, pain-free, office-based procedure. It offers low to moderate hyperopes and presbyopes an improvement in uncorrected near visual acuity while maintaining or improving their distance visual acuity.

Current management of presbyopia

Presbyopia is a physiologic inevitability that causes gradual loss of accommodation during the fifth decade of life. The correction of presbyopia and the restoration of accommodation are considered the final frontier of refractive surgery. Different approaches on the cornea, the crystalline lens and the sclera are being pursued to achieve surgical correction of this disability. There are however, a number of limitations and considerations that have prevented widespread acceptance of surgical correction for presbyopia. The quality of vision, optical and visual distortions, regression of effect, complications such as corneal ectasia and haze, anisometropia after monovision correction, impaired distance vision and the invasive nature of the currently techniques have limited the utilization of presbyopia surgery. The purpose of this paper is to provide an update of current procedures available for presbyopia correction and their limitations.

Surgical management of presbyopia

Presbyopia, the gradual loss of accommodation that becomes clinically significant during the fifth decade of life, is a physiologic inevitability. Different technologies are being pursued to achieve surgical correction of this disability; however, a number of limitations have prevented widespread acceptance of surgical presbyopia correction, such as optical and visual distortion, induced corneal ectasia, haze, anisometropy with monovision, regression of effect, decline in uncorrected distance vision, and the inherent risks with invasive techniques, limiting the development of an ideal solution. The correction of the presbyopia and the restoration of accommodation are considered the final frontier of refractive surgery. The purpose of this paper is to provide an update about current procedures available for presbyopia correction, their advantages, and disadvantages.

Reading performance after implantation of a modified corneal inlay design for the surgical correction of presbyopia: 1-year follow-up

PURPOSE

To evaluate change in different reading performance parameters after monocular ACI7000PDT corneal inlay implantation for the improvement of near and intermediate vision.

DESIGN

Prospective, interventional case series.

METHODS

Twenty-four patients were scheduled for corneal inlay implantation in the nondominant eye in a university outpatient surgery center. Naturally emmetropic and presbyopic patients between 45 and 60 years of age, with uncorrected distance visual acuity of at least 20/20 in both eyes, without any additional ocular pathology were eligible for inclusion. Bilateral uncorrected reading acuity, mean and maximum reading speed, and smallest log-scaled print size were evaluated with the standardized Radner Reading Charts. Measurements of reading parameters and reading distance were performed with the Salzburg Reading Desk (SRD). Minimum postoperative follow-up was 12 months.

RESULTS

The reading desk results showed significant changes in each parameter tested. After 12 months the mean reading distance changed from the preoperative value of 46.7 cm (95% CI: 44.1-49.3) to 42.8 cm (95% CI: 40.3-45.3, P < .004), and the mean reading acuity "at best distance" improved from 0.33 logRAD (95% CI: 0.27-0.39) to 0.24 logRAD (95% CI: 0.20-0.28, P < .005). Mean reading speed increased from 141 words per minute (wpm, 95% CI: 133-150) to 156 wpm (95% CI: 145-167, P < .003), maximum reading speed increased from 171 wpm (95% CI: 159-183) to 196 wpm (95% CI: 180-212, P = .001), and the smallest print size improved from 1.50 mm (95% CI: 1.32-1.67) to 1.12 mm (95% CI: 1.03-1.22, P < .001).

CONCLUSIONS

After ACI7000PDT implantation, there were significant changes in all tested reading performance parameters in emmetropic presbyopic patients. These 1-year results indicate that the inlay seems to be an effective treatment for presbyopia.

Improving near vision in presbyopic eyes by selective treatment of high-order aberrations

Purpose

Evaluation of improving near vision in presbyopic patients with low to moderate myopia with selective treatment of high-order aberrations (HOAs) using the ORK-CAM software aberrometer and a SCHWIND ESIRIS excimer laser. In this study, all HOAs except vertical coma were treated and the effect on near visual function was evaluated.

Setting

Horus Vision Correction Center, Alexandria, Egypt.

Methods

Twenty-six presbyopic patients (52 eyes) with low to moderate myopia were divided into two groups, A and B. The ORK-CAM software aberrometer was used in both groups to measure HOAs and design wavefront-guided treatment. All included eyes had total coma >0.2 μm. The Moria M2 mechanical microkeratome was used for flap making in both groups. Wavefront-guided laser-assisted in situ keratomileusis using ESIRIS laser was done for all eyes. In Group A (30 eyes) all HOAs were treated. In Group B (22 eyes) vertical coma was left untreated. Postoperative uncorrected distance visual acuity (UCVA), best corrected distance visual acuity (BCVA), uncorrected near acuity (UCNA), distance corrected near acuity (DCNA), best corrected near acuity with addition for near vision (BCNA), manifest refractive spherical equivalent (MRSE), HOAs, and contrast sensitivity for both groups were done preoperatively and at 3 months postoperatively.

Results

Mean age was 47.46 and 45.2 years for groups A and B, respectively. Mean preoperative MRSE was −2.37 and −2.87 D and mean preoperative total HOAs was 0.35 and 0.38 μm in groups A and B, respectively. There was no significant difference between groups regarding age, sex, preoperative MRSE, and preoperative total HOAs. After 3 months, there was no significant difference between groups in terms of UCVA, BCVA, MRSE, and contrast sensitivity. Analysis of postoperative HOAs showed significant difference in vertical coma between the two groups (P < 0.001). DCNA was significantly better in Group B (P < 0.01).

Conclusion

Treating low to moderate myopia with wavefront-guided ablation including selective treatment of HOAs might be very useful for improving visual functions. Treating all HOAs but the vertical coma improved uncorrected near acuity in presbyopic patients.

Conductive keratoplasty for the treatment of presbyopia: comparative study between post- and non-LASIK eyes

Purpose:

To evaluate the efficacy and safety of conductive keratoplasty (CK) for the treatment of presbyopia and analyze the differences in the effects between post- and non-laser in situ keratomileusis (LASIK) eyes. Clinical preoperative factors that could affect the predictability of CK were also analyzed.

Methods:

The visual and refractive outcomes of CK for the treatment of presbyopia in 14 eyes of 13 post-LASIK patients (post-LASIK group mean age 50.9 ± 3.4 years) and those of 25 eyes of 25 non-LASIK patients (non-LASIK group mean age 52.4 ± 4.0 years) were studied. The clinical efficacy, safety, stability, and predictability of CK were statistically evaluated.

Results:

The mean (logarithm of the minimum angle of resolution [logMAR] ± standard deviation [SD]) of preoperative uncorrected near visual acuity (UNVA) and manifest refraction spherical equivalent (MRSE) were 0.64 ± 0.25 diopter (D) and 0.35 ± 0.48 D, respectively, in the post-LASIK group, and 0.71 ± 0.20 D and 0.64 ± 0.61 D, respectively, in the non-LASIK group. At 6 months after CK, the mean UNVA and MRSE were 0.07 ± 0.13 D and −1.59 ± 0.86 D, respectively, in the post-LASIK group, and 0.07 ± 0.12 D and −1.06 ± 0.56 D, respectively, in the non-LASIK group. At 1 year after CK, the mean UNVA and MRSE were 0.30 ± 0.17 D and −0.58 ± 0.52 D, respectively, in the post-LASIK group, and 0.28 ± 0.34 D and −1.56 ± 0.62 D, respectively, in the non-LASIK group. There was no significant difference between the two groups in either factor at 6 months postoperative (Student’s t-test, P > 0.05). At 1 year after CK, all the treated eyes maintained corrected distance visual acuity better than −0.08 (logMAR). The mean cylindrical errors were within ±1.00 D in 100% of the post-LASIK and non-LASIK patients. As for the preoperative clinical factors evaluated for their potential relationship to the predictability of CK, none showed significant effect on the clinical outcomes.

Conclusion:

CK is demonstrated to be safe for the treatment of presbyopia in post-LASIK patients as well as in non-LASIK patients, though needed longer observation in terms of factors affecting predictability.

Topography-guided conductive keratoplasty: treatment for advanced keratoconus

PURPOSE

To evaluate the use of topography-guided conductive keratoplasty in eyes with keratoconus.

DESIGN

Interventional case series.

METHODS

We examined 21 eyes in 21 patients with advanced keratoconus. Topography-guided conductive keratoplasty was performed with intraoperative monitoring of corneal astigmatism using a surgical keratometer. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), corneal topography, manifest refraction, intraocular pressure (IOP), corneal endothelial cell counts, complications, and eventual outcomes were evaluated.

RESULTS

UCVA (logarithm of the minimal angle of resolution [logMAR]), which was 1.65 ± 0.49 preoperatively, improved to 1.04 ± 0.64 at 1 week (P < .001) and 1.12 ± 0.61 at 1 month after surgery (P < .001). BSCVA, which was 1.02 ± 0.56 preoperatively, improved to 0.76 ± 0.65 at 1 week (P = .026) and 0.76 ± 0.60 at 1 month after surgery (P = .003). Manifest refraction, which was -15.13 ± 6.66 diopters (D) before surgery, declined to -9.97 ± 6.71 D at 1 month after surgery (P = .002). Although corneal topography reverted to the preoperative pattern and UCVA and BSCVA also regressed toward preoperative values, 12 of 21 eyes were better able to tolerate and conduct normal daily activities using contact lenses. Five subjects have undergone or are considering corneal transplantation after unsatisfactory postoperative results. No serious perioperative complication was observed.

CONCLUSIONS

Topography-guided conductive keratoplasty may be effective in reshaping corneal configuration in eyes with keratoconus, without serious complications, and possibly contributed to avoiding or delaying corneal transplantation.

The role of viscoelasticity and stress gradients on the outcome of conductive keratoplasty

A mechanical analysis of the conductive keratoplasty on hyperopic eyes has been carried out, and the attention has been focused on incorporating the actual viscoelastic properties of the human corneal tissue and on the stress gradients induced by the intervention. By avoiding unnecessary complications which may obscure the essential behaviour of the model, the results are in very good agreement with the clinical and experimental findings and suggest that the major role in the commonly observed decrease of the initial degree of the refractive correction might be played by the stress gradients at the intervention spots, which are likely to influence the wound-healing. The study aims to contribute some firm mechanical roots to the predictability of the outcome of an increasingly popular technique that, notwithstanding several advantages with respect to ablative interventions, at present cannot be considered completely satisfactory.

Conductive keratoplasty followed by collagen cross-linking with riboflavin-UV-A in patients with keratoconus

PURPOSE

To evaluate the combined effect of conductive keratoplasty (CK) followed by corneal collagen cross-linking (CXL) in 2 patients with keratoconus.

METHODS

CK spots were applied on the flatter side of the cornea followed by CXL using riboflavin and UV-A light.

RESULTS

Immediately after CK, a significant corneal topographic improvement was observed. The CK effect regressed 3 months postoperatively and remained unchanged until the sixth postoperative month in both patients.

CONCLUSION

Corneal remodeling with CK in patients with keratoconus seems to have a temporary effect despite the subsequent application of CXL.

Conductive keratoplasty to treat hyperopic overcorrection after LASIK for myopia

PURPOSE

to investigate the refractive outcomes and stability of conductive keratoplasty (CK) for retreatment of myopic LASIK overcorrection.

METHODS

seven eyes (six patients) that were overcorrected after myopic LASIK by +1.00 to +2.75 diopters (D) manifest refraction spherical equivalent (MRSE) were retreated using CK. All eyes had insufficient stromal thickness for LASIK retreatment. LightTouch CK was performed at least 1 year after LASIK. Either 8 or 16 spots were applied at 7- and/or 8-mm zones on the cornea. Uncorrected distance visual acuity, manifest refraction, corrected distance visual acuity (CDVA), and postoperative complications were analyzed.

RESULTS

mean MRSE after CK at last follow-up was +0.38 ± 0.52 D (range: -0.38 to +1.13 D). The change in MRSE ranged from -0.63 to -2.38 D. Mean MRSE after CK changed from -0.60 ± 2.07 D (range: -3.38 to +1.50 D) at 1 week to +0.45 ± 0.69 D (range: -0.38 to +1.38 D) at 12 months. Two eyes experienced an initial overcorrection of -2.75 D and -3.38 D, respectively, at 1 week after CK. Cylinder ≤0.75 D was induced in four eyes, whereas one eye had a 0.75-D reduction in cylinder. All eyes had CDVA of logMAR 0.10 or better. Two eyes lost one line of CDVA and no eyes lost more than one line.

CONCLUSIONS

lighttouch CK retreatment for over-corrected myopic LASIK can reduce the hyperopia but produces minimal change in cylinder, and may be appropriate for eyes with insufficient stromal tissue for repeated excimer laser surgery. Early regression occurs commonly.

Intrastromal correction of presbyopia using a femtosecond laser system

PURPOSE

To introduce a new, minimally invasive intrastromal correction for presbyopia (INTRACOR procedure) using the TECHNOLAS femtosecond laser system (Technolas Perfect Vision GmbH).

METHODS

The INTRACOR procedure was performed in 83 eyes of 45 patients aged 44 to 67 years. Follow-up was 6 to 12 months. Data recorded included age; pre- and postoperative refraction; uncorrected distance (UDVA), intermediate, and near visual acuity (UNVA); corrected distance visual acuity (CDVA); distance corrected near visual acuity; corneal hysteresis (CH), corneal resistance factor (CRF), and asphericity; pachymetry; endothelial cell density; contrast sensitivity; and ocular aberrations.

RESULTS

At 6 months postoperatively, all 83 (100%) eyes had improved UNVA, with minimal or no change in UDVA. Twenty-two eyes were available at 12 months; UNVA improved to J1 in these eyes with continued improvement in mean UDVA. At last follow-up, a mild myopic shift in refraction was noted with only 3 (3.6%) eyes showing a 2- or 3-line decrease of UDVA, and 74 (89.2%) eyes achieved both J2 and 20/25 or better. Mean CDVA and distance corrected near visual acuity continued to improve with time. Two (2.4%) eyes lost 2 lines of CDVA at 6 months, but this did not occur in the 22 eyes seen at 1 year. Overall stability was noted in CH, CRF, pachymetry, endothelial cell density, and contrast sensitivity. Primary spherical aberrations shifted toward negative values and secondary spherical aberration shifted toward positive values. No corneal structural complications were observed.

CONCLUSIONS

The INTRACOR intrastromal procedure using the TECHNOLAS femtosecond laser is a promising procedure for presbyopia correction. It preserves the corneal epithelium and anterior stromal fibers.

LASIK for hyperopic astigmatism and presbyopia using micro-monovision with the Carl Zeiss Meditec MEL80 platform

PURPOSE

To evaluate the monocular and binocular outcomes of LASIK for a micro-monovision protocol for the correction of hyperopic astigmatism and presbyopia.

METHODS

A prospective non-comparative case series included 258 eyes of 129 consecutive patients with hyperopic astigmatism and presbyopia who were treated with LASIK-induced micro-monovision. The CRS-Master software was used to generate ablation profiles for the Carl Zeiss Meditec MEL80 excimer laser. The target refraction was piano for distance eyes (dominant eye) and between -1.00 and -1.50 diopters (D) for near eyes. Patients were followed for 1 year.

RESULTS

Mean attempted spherical equivalent refraction (SE) correction was +2.54+/-1.16 D (range: +0.25 to +5.75 D). Mean attempted cylinder was -0.52+/-0.49 D (range: -0.00 to -3.25 D). Median age was 56 years (range: 44 to 66 years). Median follow-up was 12.5 months (range: 3.3 months [early retreatment] to 18.2 months). The retreatment rate was 22%. Outcome measures after all treatments were as follows. Mean deviation from the intended SE correction was +0.09+/-0.48 D, with 79% of eyes within +/-0.50 D and 95% within +/-1.00 D. The cylinder correction ratio was 1.23+/-0.63 and the error ratio was 0.67+/-0.65. Of the distance eyes, 86% achieved uncorrected visual acuity of 20/20 and 100% achieved 20/40. Binocularly, 95% of patients achieved 20/20 and 100% achieved 20/40. Eighty-one percent of patients could read J2 and 100% could read J5. Binocularly, 95% of patients achieved 20/20 and could read J5. No eyes lost 2 or more lines of best spectacle-corrected visual acuity. A statistically significant increase was noted in contrast sensitivity at 3 and 6 cycles per degree (cpd), with no reduction at 12 and 18 cpd. The average change in refraction between 3 months and 1 year was +0.11+/-0.36 D with a change of >1.00 D in 2.6% of eyes.

CONCLUSIONS

This hyperopic micro-monovision protocol was a well-tolerated and effective procedure for treating patients with presbyopia in moderate to high hyperopia with corrections ranging up to +5.75 D. Contrast sensitivity was improved and the distance vision of near eyes was found to contribute positively to binocular distance vision compared to distance eyes monocularly.

Ex vivo multiphoton analysis of rabbit corneal wound healing following conductive keratoplasty

Ex vivo multiphoton imaging is used to characterize rabbit corneal wound healing after conductive keratoplasty (CK) procedures. CK is performed on the right eyes from eight New Zealand albino rabbits while the left eyes are punctured by a keratoplast tip without energy application. Rabbits are humanely sacrificed 1 day, 1, 2, and 4 weeks after the CK procedure. Eye balls are enucleated and placed on the microscope for multiphoton imaging. Multiphoton imaging reveals damage of corneal epithelium and stroma caused by the CK procedure and the subsequent wound healing process can be followed without histological procedures. Multiphoton excited autofluorescence images demonstrate that re-epithelilialization is accomplished within 1 week in both CK and control groups. However, epithelial hyperplasia is observed in CK corneas. In addition, stromal wounds in the control group become inconspicuous within 1 week while obvious wounds still exist in CK corneas for at least 4 weeks. Postconductive keratoplasty corneal damage and wound healing can be characterized by multiphoton microscopy without histological procedures. Our results suggest that multiphoton microscopy has potential in the clinical evaluation of corneal damage due to refractive surgery, and can be used to study and reduce the unwanted side effects of these procedures.

Radiofrequency heating of the cornea: an engineering review of electrodes and applicators

This paper reviews the different applicators and electrodes employed to create localized heating in the cornea by means of the application of radiofrequency (RF) currents. Thermokeratoplasty (TKP) is probably the best known of these techniques and is based on the principle that heating corneal tissue (particularly the central part of the corneal tissue, i.e. the central stroma) causes collagen to shrink, and hence changes the corneal curvature. Firstly, we point out that TKP techniques are a complex challenge from the engineering point of view, due to the fact that it is necessary to create very localized heating in a precise location (central stroma), within a narrow temperature range (from 58 to 76ºC). Secondly, we describe the different applicator designs (i.e. RF electrodes) proposed and tested to date. This review is planned from a technical point of view, i.e. the technical developments are classified and described taking into consideration technical criteria, such as energy delivery mode (monopolar versus bipolar), thermal conditions (dry versus cooled electrodes), lesion pattern (focal versus circular lesions), and application placement (surface versus intrastromal).

Conductive keratoplasty

PURPOSE OF REVIEW

Conductive keratoplasty is a noninvasive, in-office procedure for the correction of hyperopia, hyperopic astigmatism, and management of presbyopia. It serves as an alternative to laser-based refractive surgery with essentially no intraoperative or postoperative complications.

RECENT FINDINGS

In the past decade, photorefractive keratectomy and laser in-situ keratomileusis have been the most popular refractive surgical procedures to correct myopia, hyperopia and astigmatism. Although relatively safe, flap-related complications often result in undesirable visual acuity. Since US Food and Drugs Administration approval in 2002, conductive keratoplasty has become a promising technique to correct low to moderate hyperopia and astigmatism. The procedure was first used by Mendez and colleagues in 1993. It is a nonlaser, no cutting procedure that delivers radio-frequency energy to corneal stroma in a circular fashion to steepen the cornea. Multiple studies have shown that conductive keratoplasty offers equal or superior efficacy, predictability, stability and safety than currently used refractive procedures to correct hyperopia or hyperopic astigmatism. In addition, monovision conductive keratoplasty has been shown to be successful for the management of presbyopia.

SUMMARY

Conductive keratoplasty, an alternative to the laser-based procedure, is effective, predictable, and safe to correct low to moderate hyperopia, astigmatism, and manage presbyopia.

Investigating mechanisms of collagen thermal denaturation by high resolution second-harmonic generation imaging

We apply the technique of second-harmonic generation (SHG) microscopy to obtain large area submicron resolution image of Type I collagen from rat tail tendon as it is heated from 40 degrees C to 70 degrees C for 0-180 min. The change in the collagen structure as reflected in its SHG image is observed at length scales from submicron to hundreds of microns. We observed that heating the tendon below the temperature of 54 degrees C does not produce any change in the averaged SHG intensity. At the heating temperature of 54 degrees C and above, we find that increasing the heating temperature and time leads to decreasing SHG intensity. As the tendon is heated above 54 degrees C, the regions where the SHG signal vanish and form a tiger-tail like pattern. In addition, a decrease in the SHG signal occurs uniformly throughout the tendon. By comparing the relative SHG intensities in small and large areas, we found that the denaturation process responsible for forming the tiger-tail like pattern occurs at a higher rate than the global denaturation process occurring throughout the tendon. We also measured the fibril spacing and found that it remains constant at 1.61 +/- 0.04 micron for all heating temperature and times. The constant fibril density shows that the global denaturation process occurs at a length scale smaller than the size of the fibril. Our results show that second-harmonic generation microscopy is effective in monitoring the thermal damage to collagen and has potential applications in biomedicine.

Surgical Correction of Hyperopia

Surgical attempts to correct hyperopia have yielded varying results over the last 130 years. These techniques include the reshaping of the cornea through incisions, burns, or lamellar cuts with removal of peripheral tissue; the addition of central inlays; laser ablations; and the replacement of the crystalline lens. By examining the success of each surgical technique, the refractive surgeon may be able to make an informed decision on its indications and limitations, based on the specific patient's characteristics. Reporting the outcomes and complications of hyperopic surgery will help refine our approach to the management of an increasingly hyperopic and presbyopic population.

Prediction of heat-induced collagen shrinkage by use of second harmonic generation microscopy

Collagen shrinkage associated with denaturation from thermal treatment has a number of important clinical applications. However, individualized treatment is hindered by the lack of reliable noninvasive methods to monitor the process of collagen denaturation. We investigate the serial changes of collagen denaturation from thermal treatment of rat tail tendons at 58 degrees C by use of second harmonic generation (SHG) microscopy. We find that rat tail tendon shrinks progressively from 0 to 9 min of thermal treatment, and remains unchanged in length upon further thermal treatment. The SHG intensity also decreases from 0 to 9 min of thermal treatment and becomes barely detectable from further thermal treatment. Collagen shrinkage and the SHG intensity are well correlated in a linear model. In addition, SHG imaging reveals a tiger-tail-like pattern of collagen denaturation. The bands of denatured collagen progressively widen from increased thermal treatment and completely replace the adjacent bands of normal collagen after 9 min of thermal treatment. Our results show that collagen denaturation in rat tail tendon from thermal treatment is inhomogeneous, and that SHG intensity can be used to predict the degree of thermally induced collagen shrinkage. With additional development, this approach has the potential to be used in biomedical applications.

Photorefractive Keratectomy and LASIK for the Correction of Hyperopia: 2-year Follow-up

PURPOSE

To evaluate the efficacy and safety of photorefractive keratectomy (PRK) and LASIK in the correction of hyperopia.

METHODS

A retrospective study was conducted on 100 eyes of 56 patients with a mean hyperopia of +2.85 +/- 1.1 diopters (D) undergoing PRK and 100 eyes of 50 patients with a mean hyperopia of +4.49 +/- 1.2 D undergoing LASIK. A Zeiss Meditec MEL 70 G scan laser was used.

RESULTS

After 24-month follow-up in the PRK group (100 eyes), the mean manifest refractive spherical equivalent (MRSE) was +0.34 +/- 0.92 D (36% +/- 0.5 D). Mean uncorrected visual acuity (UCVA) was 0.87 +/- 0.1; 8 (8%) eyes gained 1 line, 80 (80%) eyes had no loss or gain of lines, 10 (10%) eyes lost 1 line, and 2 (2%) eyes lost 2 lines. In the LASIK group (100 eyes), at 24-month follow-up, the mean MRSE was +0.29 +/- 0.66 D (70% +/- 0.5 D). Mean UCVA was 0.89 +/- 0.1; 6 (6%) eyes gained 2 lines, 10 (10%) eyes gained 1 line, 78 (78%) eyes had no loss or gain of lines, and 6 (6%) eyes lost 1 line.

CONCLUSIONS

Photorefractive keratectomy and LASIK were both effective and safe in the correction of hyperopia. However, PRK manifested an initial temporary myopic overshoot followed by a hyperopic regression over 24-month follow-up (P < .01) whereas LASIK was associated with a faster refractive stability.

Surgical management of presbyopia

Presbyopia is age-related reduction in amplitude of accommodation and the loss of the ability to change the eye's focus from far to near. It is the one of the most common age-related ailment. Traditional methods such as spectacle glasses or contact lenses are still the most widely used for correction of the problem. This article is an attempt to review the surgical options available for presbyopia.

Conductive keratoplasty: histological study of human corneas

PURPOSE

To determine the morphologic changes in human corneas over time following radiofrequency-based conductive keratoplasty (CK) treatment.

DESIGN

Prospective, observational case series.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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

PURPOSE

To assess the outcomes of conductive keratoplasty (CK) for patients with complications related to LASIK or photorefractive keratectomy (PRK).

DESIGN

Retrospective, noncomparative, interventional case series.

PARTICIPANTS

Sixteen eyes of 15 patients were treated using CK after complications of initial LASIK or PRK surgeries. Five cases are described in detail.

INTERVENTION

Rehabilitative CK was performed.

MAIN OUTCOME MEASURES

Uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA), refractive error, keratometry, topography analysis, and a subjective assessment of visual quality.

RESULTS

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.

CONCLUSIONS

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.

Characterizing the thermally induced structural changes to intact porcine eye, part 1: second harmonic generation imaging of cornea stroma

We characterize the structural changes of porcine corneal structures from 25 to 90 degrees C using second harmonic generation (SHG) microscopy. Our results show that porcine stroma undergoes several distinct stages of structural changes between 25 and 90 degrees C. A decrease in SHG intensity from 30 to 45 degrees C and the existence of SHG intensity peaks at 53, 65, and 77 degrees C correlate to distinct structural alterations of the corneal stroma. At higher temperatures, the SHG intensity decreases and a baseline in SHG signal is reached at 90 degrees C. Our results demonstrate that SHG microscopy is a useful technique for obtaining qualitative and quantitative information of thermally treated corneal fibers without histological or labeling procedures. With additional developments, SHG imaging may be developed into an effective imaging technique for in vivo characterization of cornea structural changes.

Monitoring the thermally induced structural transitions of collagen by use of second-harmonic generation microscopy

The thermal disruption of collagen I in rat tail tendon is investigated with second-harmonic generation (SHG) microscopy. We investigate its effects on SHG images and intensity in the temperature range 25 degrees-60 degrees C. We find that the SHG signal decreases rapidly starting at 45 degrees C. However, SHG imaging reveals that breakage of collagen fibers is not evident until 57 degrees C and worsens with increasing temperature. At 57 degrees C, structures of both molten and fibrous collagen exist, and the disruption of collagen appears to be complete at 60 degrees C. Our results suggest that, in addition to intensity measurement, SHG imaging is necessary for monitoring details of thermally induced changes in collagen structures in biomedical applications.

Intraocular Pressure Measurements After Conductive Keratoplasty

PURPOSE

To determine the possible impact of conductive keratoplasty (CK) on intraocular pressure (IOP) measurements.

METHODS

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).

RESULTS

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.

CONCLUSIONS

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

PURPOSE

To evaluate the treatment of surgically induced astigmatism intraoperatively during conductive keratoplasty (CK) for correcting hyperopia.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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 degrees 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 degrees 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 degrees 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.

Treatment of Presbyopia With Conductive Keratoplasty??

PURPOSE

To provide 6-month results of a 1-year clinical trial evaluating conductive keratoplasty (CK) for the treatment of presbyopic symptoms in emmetropic and hyperopic eyes.

METHODS

A total of 143 patients with presbyopic symptoms were enrolled in this 1-year United States FDA clinical trial and treated to improve near vision in 1 eye (unilateral treatment). In addition, 33 fellow eyes were treated to improve distance vision (bilateral treatment). For near vision correction, the target refraction was up to -2.0 D in the nondominant eye, and for distance vision correction, 0.0 D. Enrolled patients had a preoperative spherical equivalent of plano to +2.00 D, no more than 0.75 D of refractive astigmatism, and were 40 years of age or older. No retreatments were performed.

RESULTS

Of the eyes treated for near, 77% had uncorrected near vision of J3 or better at 6 months postoperatively. A total of 85% of all patients had binocular distance UCVA of 20/25 or better along with J3 or better near, a combination that represents functional acuity for a presbyope. Sixty-six percent of eyes treated for near had a manifest refractive spherical equivalent (MRSE) within +/- 0.50 D of intended at 6 months. In 89% of eyes, the MRSE changed 0.05 D or less between 3 and 6 months postoperatively. After month 1, the incidence of variables associated with safety was 1% or lower. Seventy-six percent were very satisfied or satisfied with their procedure.

CONCLUSIONS

CK appears to be very safe and effective in producing functional visual acuity in presbyopic eyes up to 6 months following the procedure. Patient satisfaction with the procedure is similar to that of monovision LASIK.

Videokeratography in Conductive Keratoplasty

PURPOSE

We used EyeSys videokeratography to evaluate corneal shape changes induced by conductive keratoplasty, a procedure that utilizes radio frequency energy to alter corneal shape to correct hyperopia.

METHODS

Follow-up data were available for 19 eyes (out of 24 eyes of 13 patients). Preoperative spherical hyperopia ranged from +0.75 to +3.25 D with astigmatism <0.75 D. Manifest refractive spherical equivalent refraction (MRSE), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), topographical parameter predicted corneal acuity (PCA), corneal uniformity index (CU Index), regular astigmatism, total astigmatism, average simulated keratometry (Avg Sim K), effective refractive power, and asphericity were measured preoperatively and at 6 and 12 months postoperatively.

RESULTS

Twelve months postoperatively, mean PCA, CU Index, and BSCVA were maintained at preoperative levels. Mean UCVA (LogMAR) improved from 0.53+/-0.21 to 0.10+/-0.19 (P<.05) with a mean MRSE change from +1.62+/-0.76 D to -0.06+/-0.84 D (P<.05) from preoperative to 12 months postoperative. Mean asphericity increased +0.044+/-0.24 D (P>.05), mean Avg Sim K increased 1.88+/-0.72 D (P<.05), mean effective refractive power increased 1.71+/-0.79 D (P<.05), mean cylinder (cycloplegic refraction) increased 0.19+/-0.36 D (P<.05), mean regular astigmatism increased 0.25+/-0.49 D (P>.05), and mean irregular astigmatism decreased 0.01+/-0.13 D (P>.05) from preoperative to 12 months after conductive keratoplasty.

CONCLUSIONS

Avg Sim K and effective refractive power changes support the refractive results; 12-month postoperative maintenance of BSCVA, PCA, and CU Index suggest the procedure is safe. Conductive keratoplasty induced a slight regular astigmatism in some eyes, which decreased with time. The increase in mean corneal asphericity indicated possible induction of central and peripheral cornea changes.

Laser in situ Keratomileusis for Residual Hyperopic Astigmatism After Conductive Keratoplasty

PURPOSE

To report a case of laser in situ keratomileusis (LASIK) in a patient with previous conductive keratoplasty.

METHODS

A 48-year-old man underwent conductive keratoplasty for low hyperopic astigmatism (manifest refraction OD: +2.25 -0.50 x 77 degrees; OS: +2.50 -0.50 x 105 degrees). Three months postoperatively, UCVA was 20/25 and BSCVA was 20/20 in both eyes; manifest refraction OD: -0.25 -0.75 x 110 degrees; OS: +0.75 -0.75 x 50 degrees. Sixteen months after the operation, regression of refractive outcome was (manifest) OD: +1.75 -1.25 x 90 degrees; OS: +2.50 -0.50 x 85 degrees; UCVA was 20/40 in the right eye and 20/63 in the left eye and BSCVA was 20/20 in both eyes. LASIK was performed for hyperopic regression in the left eye using an automated microkeratome (Alcon SKBM, 130-microm plate; Aesculap-Meditec MEL 70 excimer laser).

RESULTS

LASIK was uneventful and no intraoperative or postoperative complications related to the previous conductive keratoplasty procedure or LASIK were observed. Three months after LASIK and 19 months after the initial conductive keratoplasty, the patient's left eye was emmetropic; UCVA was 20/20(-2), BSCVA was 20/20 and manifest refraction was +0.25 -0.25 x 35 degrees. There was a uniform increase in topographical steepening. Visual acuity, refraction and topographic findings remained unchanged at 6 months.

CONCLUSIONS

Even though our experience is limited, treatment of hyperopia with LASIK in an eye with refractive regression following previous conductive keratoplasty resulted in a predicted refractive outcome, with no complications, and improvement in visual acuity at 6 months follow-up.

Ring electrode for radio-frequency heating of the cornea: modelling and in vitro experiments

Radio-frequency thermokeratoplasty (RF-TKP) is a technique used to reshape the cornea curvature by means of thermal lesions using radio-frequency currents. This curvature change allows refractive disorders such as hyperopia to be corrected. A new electrode with ring geometry is proposed for RF-TKP. It was designed to create a single thermal lesion with a full-circle shape. Finite element models were developed, and the temperature distributions in the cornea were analysed for different ring electrode characteristics. The computer results indicated that the maximum temperature in the cornea was located in the vicinity of the ring electrode outer perimeter, and that the lesions had a semi-torus shape. The results also indicated that the electrode thickness, electrode radius and electrode thermal conductivity had a significant influence on the temperature distributions. In addition, in vitro experiments were performed on rabbit eyes. At 5 W power, the lesions were fully circular. Some lesions showed non-uniform characteristics along their circular path. Lesion depth depended on heating duration (60% of corneal thickness for 20 s, and 30% for 10 s). The results suggest that the critical shrinkage temperature (55-63 degrees C) was reached at the central stroma and along the entire circular path in all the cases.