Conductive Keratoplasty Research Articles

BCLA CLEAR Presbyopia: Management with corneal techniques

Corneal techniques for enhancing near and intermediate vision to correct presbyopia include surgical and contact lens treatment modalities. Broad approaches used independently or in combination include correcting one eye for distant and the other for near or intermediate vision, (termed monovision or mini-monovision depending on the degree of anisometropia) and/or extending the eye’s depth of focus [1]. This report reviews the evidence for the treatment profile, safety, and efficacy of the current range of corneal techniques for managing presbyopia.The visual needs and expectations of the patient, their ocular characteristics, and prior history of surgery are critical considerations for patient selection and preoperative evaluation. Contraindications to refractive surgery include unstable refraction, corneal abnormalities, inadequate corneal thickness for the proposed ablation depth, ocular and systemic co-morbidities, uncontrolled mental health issues and unrealistic patient expectations.Laser refractive options for monovision include surface/stromal ablation techniques and keratorefractive lenticule extraction. Alteration of spherical aberration and multifocal ablation profiles are the primary means for increasing ocular depth of focus, using surface and non-surface laser refractive techniques. Corneal inlays use either small aperture optics to increase depth of field or modify the anterior corneal curvature to induce corneal multifocality. In presbyopia correction by conductive keratoplasty, radiofrequency energy is applied to the mid-peripheral corneal stroma, leading to mid-peripheral corneal shrinkage and central corneal steepening. Hyperopic orthokeratology lens fitting can induce spherical aberration and correct some level of presbyopia.Postoperative management, and consideration of potential complications, varies according to technique applied and the time to restore corneal stability, but a minimum of 3 months of follow-up is recommended after corneal refractive procedures. Ongoing follow-up is important in orthokeratology and longer-term follow-up may be required in the event of late complications following corneal inlay surgery.

Dielectric properties of the non-glycated and in vitro methylglyoxal-glycated cornea of the rabbit eye

The dielectric properties of the non-glycated and in vitro methylglyoxal-glycated cornea of the rabbit eye were tested in the frequency range of 200 Hz to 100 kHz of the electric field and at temperatures of 25 to 140 °C. The denaturation temperature (Td) for the non-glycated cornea and the non-enzymatically glycated cornea are approximately 45 and 55 °C, respectively. The mechanism of proton conduction up to Td in a glycated cornea requires more energy, i.e. more than twice the activation energy (ΔH) than in non-glycated tissue. The dielectric spectra for both examined tissues showed the same characteristic frequency of about 7 kHz assigned to the orientation relaxation time of the polar side groups inside the corneal stroma. These results may be useful in the surgical treatment of the cornea using conductive keratoplasty and in tissue engineering for clinical applications to regenerate this tissue. The medical use of these physico-biological techniques is important because the human cornea protects all eye tissues from various environmental factors.

Hocus pocus: Breaking the curse of presbyopia.

Research and awareness on refractive solutions for presbyopia, commonly known as the "Curse of the 40's," is essential as a large population in the world suffer from vision impairments. Population-based surveys have shown that one billion people in the world are in presbyopic age. Many structural and physiological changes occur in the eye with the onset of presbyopia, including the decrease in amplitude of accommodation. At present, various static and dynamic techniques have been attempted to give presbyopes good vision at near-, intermediate-, and far-viewing distances. The aim of the video is to familiarize the modern-day ophthalmologists to these modalities. In this video, we tried to summarize the indications and contraindications of presbyopic laser. Preoperative investigations like dominance testing and micro monovision testing are described. The role of neuroadaptation and patient counselling is emphasized. Static techniques described in the video include spectacles, contact lenses, surgical options like corneal inlays and onlays, corneal laser ablation, conductive keratoplasty, corneal implant lenses, INTRACOR and IOLs. Dynamic presbyopia correction (accommodative) is always surgical. This is split into lenticular (accommodating IOLs, piggyback, lens refilling, lentotomy) and scleral treatment (laser-assisted presbyopia reversal and scleral expansion bands). The types of corneal laser ablation, which is otherwise very confusing, is elaborated in a step-wise manner here. The difference in approach of PresbyLasik (Nidek), Presbyond (Zeiss) - Laser Blended Vision, PresbyMax (Schwind), INTRACOR (Technolas) are explained with examples. Each approach has its pros and cons. Our challenge as a surgeon is to identify the best combination for the patient. This video illustrates the treatment options which can help break the curse of presbyopia. https://youtu.be/rTxMIqMrgaw.

Anterior segment OCT findings and atypical refractive changes secondary to Epstein-Barr virus–associated nummular keratitis

Introduction: This case study described refractive changes that can occur in the setting of Epstein-Barr virus (EBV)-associated nummular keratitis (NK) and highlighted the role that anterior segment optical coherence tomography can serve in diagnosis and management of this disease. Patient and Clinical Findings: A 15-year-old girl developed subepithelial and anterior stromal corneal lesions and experienced progressive decline in the corrected distance visual acuity. She also developed a significant myopic shift with increased keratometric and refractive astigmatism. Diagnosis, Intervention, and Outcomes Targeted laboratory testing was performed. A diagnosis of chronic EBV-associated NK was made, and the patient was treated with systemic valacyclovir and topical steroids. Clinical appearance of lesions and corrected distance visual acuity improved, although refractive and keratometric changes persisted. Conclusions: Significant and persistent refractive changes can occur in the setting of EBV-associated NK, similar to those seen after conductive keratoplasty. Anterior segment optical coherence tomography can be a potentially helpful supplementary diagnostic imaging modality to avoid invasive testing in such cases.

Irregular Astigmatism Induced by Irregular Epithelial Remodeling After Conductive Keratoplasty and Transepithelial CXL

PURPOSE: To describe the evaluation and management of irregular astigmatism induced by persistent irregular epithelial remodeling in the absence of persistent underlying stromal curvature irregularity following photorefractive keratectomy (PRK) re-treatment after remote myopic laser in situ keratomileusis (LASIK) with subsequent conductive keratoplasty (CK) and transepithelial corneal cross-linking (CXL). METHODS: Case report. RESULTS: A 41-year-old woman presented for evaluation 1 year after developing blurred vision. She had irregular astigmatism in her right eye following PRK re-treatment for regression after remote myopic LASIK, with a subsequent combined CK and modified transepithelial CXL procedure 1 month after PRK. Scheimpflug tomography demonstrated a post-myopic ablation pattern with an apparent decentered optical zone. Anterior segment optical coherence tomography (AS-OCT) revealed an irregular epithelial thickness pattern, with an asymmetric focal region of epithelial thickness para-centrally temporally. Superficial keratectomy was performed. Following the procedure, the patient's uncorrected distance visual acuity improved by two lines to 20/20, and her subjective blur symptoms resolved and remained stable during 12 months of follow-up. Repeat AS-OCT demonstrated a more uniform epithelial thickness pattern. Scheimpflug tomography showed resolution of the optical zone decentration, confirming that the irregular epithelial remodeling caused the curvature irregularity, and the underlying stromal curvature was not significantly irregular at the time of treatment. CONCLUSIONS: Although uncommon, irregular epithelial remodeling can occur without permanent underlying stromal irregularity. The authors surmise that a temporary induced stromal curvature change from combined CK and transepithelial CXL regressed, but epithelial remodeling did not return to the anticipated regular postoperative pattern. This phenomenon would be unrecognizable in the absence of epithelial mapping and highlights the need for thorough evaluation and targeted management strategies to improve epithelial regularization. [ Journal of Refractive Surgery Case Reports . 2021;1(2):e23–e30.]

Outcomes of Conductive Keratoplasty Combined with Corneal Crosslinking in Advanced Ectatic Corneal Disease

PurposeTo assess the effectiveness of a novel treatment for patients with advanced corneal ectasia and loss of visual acuity (VA). Conductive keratoplasty (CK) is performed to improve VA followed by epithelium-on (epi-on) corneal crosslinking (CXL) to stabilize the cornea after CK.MethodsRetrospective, exploratory cohort study. Patients with keratoconus or postsurgical ectasia and best spectacle-corrected distance VA (CDVA) ≤ 20/40 were included. Conductive keratoplasty was performed (ViewPoint CK System, Refractec, Inc., Bloomington, MN); followed a day later by epi-on CXL (CXLUSA/CXLO, Bethesda, MD/CXLO Encinitas, CA). Measures included uncorrected distance visual acuity (UDVA) and CDVA, as well as refractive and tomographic measures and tomographic indices.ResultsData from 50 eyes of 45 patients were analyzed. Mean follow-up was 15.1 ± 12.2 months (range: 2 to 51). Overall, UDVA and CDVA improved postoperatively. Subjective refraction and tomographic metrics did not show consistent changes, but changes in tomographic indices were associated with treatment follow-up time. At the 1-year visit, mean UDVA significantly improved over baseline (P = 0.009) by approximately 3 lines; mean CDVA improved significantly (P = 10−5) by approximately 2 lines. No eye lost lines of CDVA. Change in the Index of Surface Variance (ISV) was associated with treatment, and the D-Index trended over follow-up time.ConclusionConductive keratoplasty with a proprietary epi-on CXL treatment improved vision in patients with advanced ectasia This CK/epi-on CXL treatment offers the possibility of improved VA for patients with compromised vision due to ectasia.

Corneal cross-linking (CXL) combined with refractive surgery for the comprehensive management of keratoconus: CXL plus.

The past two decades have witnessed an unprecedented evolution in the management of keratoconus that demands a holistic approach comprising of inhibiting the ectatic progression as well as visual rehabilitation. The advent of corneal cross-linking (CXL) in the late 1990s resulted in long-term stabilization of the ectatic cornea along with limited reduction in corneal steepening and regularization of corneal curvature. However, CXL as a standalone procedure does not suffice in rehabilitating the functional vision especially in patients who are unwilling or intolerant towards contact lenses. The concept of “CXL plus” was proposed which incorporates adjunctive use of refractive procedures with CXL in order to overcome the optical inefficiency due to corneal irregularity, decrease the irregular astigmatism, correct the residual refractive error and improve functional visual outcome in keratoconus. Several refractive procedures such as conductive keratoplasty (CK), photorefractive keratectomy (PRK), transepithelial phototherapeutic keratectomy (t-PTK), intrastromal corneal ring segments (ICRS) implantation, phakic intraocular lens (PIOL) implantation and multiple other techniques have been combined with CXL to optimize and enhance the CXL outcome. This review aimed to summarize the different protocols of CXL plus, provide guidelines for selection of the optimum CXL plus technique and aid in decision-making for the comprehensive management of cases with primary keratoconus in addition to discussing the future and scope for innovations in the existing treatment protocols.

Combined Protocols for Corneal Collagen Cross-Linking with Photorefractive Surgery for Refractive Management of Keratoconus: Update on Techniques and Review of Literature.

With the development and gradual dissemination of corneal collagen cross-linking (CXL) in the twenty-first century as an early treatment for keratoconus, the management paradigm has shifted to include a greater focus on complete refractive correction for these patients. Though supplemental hard contact lens therapy remains a mainstay of visual rehabilitation in keratoconus, there has been increasing appeal in a completely surgical approach by combining CXL with adjuvant refractive procedures to both halt the ectatic process and enhance functional visual outcomes. Collectively termed “CXL plus” procedures, several combined protocols have been studied to various degrees in conjunction with CXL, involving photorefractive keratectomy (PRK), transepithelial phototherapeutic keratectomy (PTK), conductive keratoplasty (CK), intrastromal corneal ring segments (ICRS) implantation, phakic intraocular lens (PIOL) implantation, or multiple of these techniques together. The scope of this review aims to encompass a summary of current CXL protocols and present the current status of studies involving adjunctive keratorefractive procedures combined with CXL. By discussing the results to date of these CXL plus protocols, we can assess what further areas of investigation are necessary within this field as the next step to optimizing treatment modalities and outcomes for our keratoconus patients, regardless of disease severity.

Surgical options for the correction of presbyopia

Presbyopia is an age-related eye condition, and its most prominent sign is the reduction in the amplitude of accommodation, resulting in the disability to modify the focus from far to near of the eyes.Surgical therapy of presbyopia still remain great challenge for refractive surgeons.Surgical strategies of presbyopia include extraocular (corneal or scleral) and intraocular procedures, such as excimer laser surgery, conductive keratoplasty, INTRACOR, corneal inlays, multiple types of multi-focal or accommodating intraocular lens, laser-assisted presbyopia reversal, scleral expansion bands, etc.Each procedure owns its unique advantages and disadvantages.This review attempted to address the surgical options available and likely to be available in the near future and discuss the key problems in presbyopia procedures. Key words: Presbyopia; Refraction, ocular; Ophthalmic surgical procedures

Evolution of refractive surgeries

The use of surgical procedures to correct refractive errors of the eye has come a long way. The two main types are corneal procedures and intraocular procedures. Corneal procedures have evolved from thermokeratoplasty, keratotomies, epikeratoplasty, laser ablation, conductive keratoplasty, and collagen cross-linking. Intraocular procedures involve phakic intraocular lens (IOL), toric IOL, refractive lens exchange, and accommodating IOLs. Various physicists and ophthalmologists have played a role in this saga. From the idea of using thermal energy to shrink corneal tissue to using femtosecond laser, this article highlights the important landmarks in the history of evolution of refractive surgeries. Refractive surgeries form an ever-growing specialty of ophthalmology with addition of novel techniques with every quantum of time.

Visco-elastic and thermal-induced damaging in time-dependent reshaping of human cornea after conductive keratoplasty

With the aim of investigating the role played by both the radiofrequency-induced thermal damaging and the viscoelasticity of the tissue in human cornea surface reshaping—time dependent key factors for the success of the surgical outcome in the short-term post-intervention period—the Conductive Keratoplasty (CK, a surgical technique used for the correction of farsightedness) has been simulated with reference to the protocol adopted for moderate hyperopia. By means of a transient thermal analysis, the amount of the local thermal-induced tissue damaging has been computed in order to remap the constitutive properties of the corneal tissue. Successively, a mechanical non-linear analysis has been performed for predicting the corneal curvature around the optical zone during the post-surgery period. The study aims to contribute some firm thermo-mechanical roots to better understand the corneal tissue response to thermal insults and its reshaping predictability in a long period.

Corneal Surgical Approach in the Treatment of Presbyopia

Purpose: The aim of this paper is to outline the various corneal approaches to the treatment of presbyopia and discuss their effectiveness Method: Most corneal surgical procedures involve LASIK. Supracor uses a progressive ablation profile to provide an aberration optimized smooth transition from distance to near correction. In presbyLASIK a hyper positive area is created at the centre of the cornea for near vision and the periphery provides a focus for distance. The Intracor procedure is an intra-stromal treatment using a femto-second laser. It creates concentric rings with the stroma. These bring about central steepening of the cornea. Monovision corrects one eye for distance and the less dominant eye for near. Conductive keratoplasty uses heat generated by high radio frequency current to alter the corneal stroma. Corneal small aperture implants or inlays are inserted into the cornea through a pocket created by femtosecond laser to improve the near and intermediate vision. Results: Supracor offers the best prospect but the high retreatment rate is a major drawback. Intracor and corneal inlays offer the best hope for elimination of reading glasses but reduction of distance vision, loss of binocularity and reduction of the effect overtime limit their use. Monovision for a selective group of patient is still the best alternative. Conclusions: There is no ideal corneal surgical approach to presbyopia. The future may involve more than one approach, perhaps a corneal approach for patients under 50 and a lens solution for older patient. The ideal procedure and best outcome is still some way off.

Combined astigmatic keratotomy and conductive keratoplasty to correct high corneal astigmatism

To determine the safety, efficacy, and predictability of combined astigmatic keratotomy (AK) and conductive keratoplasty (CK) for treating high corneal astigmatism. University of California-Los Angeles, Los Angeles, California, USA. Retrospective case series. From January 1, 2004, to December 31, 2009, AK and CK were performed in eyes with corneal astigmatism of 5.0 diopters (D) or more after keratoplasty or trauma. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, spherical equivalent (SE), defocus equivalent, mean astigmatism, efficacy index, and complications were evaluated. In 11 eyes of 11 patients, the mean UDVA improved from 1.54 logMAR ± 0.50 (SD) preoperatively to 0.69 ± 0.62 logMAR 3 months postoperatively (P < .001) and the mean CDVA from 0.55 ± 0.62 logMAR to 0.12 ± 0.11 logMAR (P = .028). The mean SE and mean defocus equivalent decreased from -1.25 ± 5.06 D to 3.13 ± 3.06 D (P = .15) and from 7.98 ± 4.41 D to 6.97 ± 3.73 D (P = .45), respectively; these changes were not statistically significant. The mean absolute astigmatism decreased from 10.25 ± 4.71 D to 4.31 ± 2.34 D (P < .001). The mean absolute orthogonal and mean oblique astigmatism showed a statistically significant decrease. The efficacy index was 0.82. One case of wound gape after AK required suturing. No infectious keratitis, corneal perforation, or graft rejection occurred. Results indicate that combined AK and CK is safe and effective for correcting high corneal astigmatism after surgery or trauma.

Dielectric relaxation of normothermic and hypothermic rat corneas

This paper aims at the presentation of the results of in vitro research on the dielectric properties of the cornea specimen collected from the rats subjected to in vivo hypothermia.The average values of the relative permittivity and dielectric loss are about 40% higher for the hypothermic cornea than those for the normothermic tissue at the same water content of 12% for both samples and at 25°C. Whereas, at 50°C this effect of increase in the dielectric properties of the hypothermic cornea when compared to the normothermic one is observed clearly only in the relative permittivity of about 19%. In the temperature range of 25–50°C, the activation energy of conductivity associated with the release of loosely bound water takes the average values of 45kJ/mol and 30kJ/mol for the normothermic and hypothermic corneas, respectively. The study provided information on dielectric polarization and conductance mechanisms in the cornea which may be helpful in interpreting clinical results of human cornea examination, currently obtained by means of such electrodiagnostic methods as conductive keratoplasty, electroretinography or electrooculography.

Surgical treatment of presbyopia

Presbyopia is the progressive reduction in the ability to focus on near objects, and as an age-related condition, the prevalence of presbyopia is expected to increase with the aging of society. A number of corneal surgical procedures are available for the treatment of presbyopia, including monovision laser in situ keratomileusis (LASIK)/ laser-assisted subepithelial keratomileusis (LASEK), conductive keratoplasty, presbyopic LASIK, and corneal inlay. Implantation of presbyopiacorrecting intraocular lenses (IOLs), such as refractive/diffractive IOLs or accommodating IOLs, is also an option. Despite the variety of treatment options available, a perfect solution has yet to be developed and patients may present with visual or optical complications such as halos, glare, or decreased contrast sensitivity. As such, careful selection and customization of treatment is essential, based on patients’ individual needs and requirements for vision.

Indications for and Outcomes of Tertiary Referrals in Refractive Surgery

To review the spectrum of disease, symptomatology, and management offered to patients referred for a second opinion after refractive surgery. A prospective cohort study was done on all patients referred from October 1, 2006, to September 30, 2011, to a tertiary eye clinic after refractive surgery of any kind (ie, corneal laser surgery, conductive keratoplasty, radial keratotomy, phakic implants, refractive lens exchanges, or any combination thereof). Data analysis was performed on all demographic and clinical aspects of this cohort, including the initial complaint, type of referral, number of complaints, procedure previously performed, diagnosis at our center, type of advice given, and rate and type of surgical intervention. One hundred thirty-one eyes (69 patients) were included. Corneal refractive surgery was performed in 82% (108 eyes), and 11% (14 eyes) were seen after phakic intraocular lens (PIOL) implantation and 7% (9 eyes) after refractive lens exchange. The most common diagnoses were tear film dysfunction (30 eyes, 23%), residual refractive error (25 eyes, 19%), and cataract (20 eyes, 15%). Most patients (42 patients, 61%) were treated conservatively. In 27 patients (39%), 36 eyes (28%) were managed surgically. Severe visual loss was seen in 1 eye. No major problems were found in most second opinions after refractive surgery referral. Dry eyes, small residual refractive error, or higher-order aberrations were the most common complaints. Surgical intervention was needed in 36 eyes (28%), almost half of which were cataract extractions. Severe visual loss was seen in 1 eye with a PIOL. There was no incidence of severe visual loss in keratorefractive and refractive lens exchange procedures.

Conductive keratoplasty: an approach for the correction of residual hyperopia in post-lasik pseudophakia.

Although there are many formulae for the calculation of intraocular lens power in the eyes with previous kerato-refractive surgeries, unexpected refractive bias still exists. Hyperopic bias is particularly disliked because it affects both uncorrected distance and near visual acuity. Surgical treatment of the residual hyperopia for the eyes with both laser in situ keratomileusis and cataract surgery remains to be a big problem. Conductive keratoplasty has been shown to be an effective, safe and predictable method for low and moderate hyperopia in the pseudophakic eyes or in the eyes with kerato-refractive surgeries. However, the efficacy and safety of conductive keratoplasty in the correction of residual hyperopia after both corneal and lens refractive surgeries has not been reported. Herein, we reported the surgical correction with conductive keratoplasty for cases of residual hyperopia with/without astigmatism after previous laser in situ keratomileusis for high myopia and following phacoemulsification combined with posterior intraocular lens implantation for complicated cataract.

Comparing the rate of regression after conductive keratoplasty with or without prior laser-assisted in situ keratomileusis or photorefractive keratectomy

Purpose:To assess the regression rate of conductive keratoplasty (CK) in patients with or without previous laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK).Setting:University of Utah, Medical School, John A. Moran Eye Center, Salt Lake City, Utah.Materials and Methods:A retrospective, age-matched chart review identified records of 6 patients who underwent CK after refractive surgery and 12 patients who underwent CK without prior refractive surgery. The main outcome measures were postoperative uncorrected and corrected visual acuities and refraction changes over time.Results:Preoperatively, the mean manifest refraction spherical equivalent (MRSE) of the 15 eyes (12 patients) that underwent CK without refractive surgery was 0.83 diopters (D) and the 7 eyes (6 patients) that underwent CK after refractive surgery had an average MRSE of 0.27 D. Postoperatively, the mean MRSE of the refractive surgery patients was -0.86 D at 6 months, regressing to -0.67 D at 12 months. The postoperative MRSE in the eyes without refractive surgery was -0.58 D. at 6 months, regressing to -0.38 D at 12 months. The rate of regression was linear in both groups, calculated at 0.033 D per month in all patients.Conclusions:Patients with previous LASIK or PRK showed a greater treatment response to CK but regressed at a similar rate as those eyes without prior LASIK or PRK. Overall CK is a safe procedure that inevitably regresses.

Clinical Outcomes of Monovision Induced by Presbyopic Correcting Conductive Keratoplasty

Clinical Outcomes of Monovision Induced by Presbyopic Correcting Conductive Keratoplasty

Conductive keratoplasty for symptomatic presbyopia following monofocal intraocular lens implantation

To evaluate the visual outcomes of conductive keratoplasty for relief of symptomatic presbyopia of pseudophakia with monofocal intraocular lens implantation. It was a prospective clinical study and set in Eye Center, Second Affiliated Hospital, Zhejiang University. This study comprised 27 eyes from 27 patients with presbyopia symptom. The patients received conductive keratoplasty via monovision approach after monofocal intraocular lens implantation and were followed up at 1 week and 1, 3, 6 and 12 months postoperatively. The main outcomes including uncorrected near visual acuity, uncorrected distance visual acuity, best spectacle-corrected visual acuity, manifest refraction spherical equivalent, keratometric astigmatism, contrast and glare sensitivity, spherical aberration and pseudoaccommodation were evaluated. Twelve months after conductive keratoplasty, the binocular uncorrected near visual acuity was significantly improved from logMAR 0.88 ± 0.16 preoperatively to logMAR 0.30 ± 0.13 (P < 0.05); the binocular uncorrected distance visual acuity and best spectacle-corrected visual acuity remained unchanged; manifest refraction spherical equivalent was significantly reduced from 0.01 ± 0.68 D preoperatively to -1.68 ± 0.39 D (P < 0.05); spherical aberration was increased from 0.266 ± 0.204 µm preoperatively to 0.358 ± 0.277 µm (P < 0.05), and pseudoaccommodation was from 1.38 ± 0.38 D to 1.73 ± 0.61 D (P < 0.05). Conductive keratoplasty is a safe and effective method for relief of symptomatic presbyopia of pseudophakia with monofocal intraocular lens implantation.