Synthetic corneal inlays

Unilateral Keratectasia Treated with Femtosecond Fashioned Intrastromal Corneal Inlay

Purpose:

In this case report, we describe the surgical procedure of corneal inlay preparation and corneal pocket creation using a femtosecond laser system.

Case Report:

A 7-year-old girl who presented with unilateral paracentral corneal thinning underwent the surgical procedure of corneal inlay. Preoperatively, the refraction was +10.00-6.00 × 170. One month after the procedure, astigmatism and hyperopia were decreased and the refraction was +5.00-1.25 × 110.

Conclusion:

Femtosecond laser–assisted pocket creation for the implantation of corneal inlays offers accuracy of pocket parameters, enhancing predictability, resulting in better final outcomes, and improving the safety of the procedure.

Cataract surgery on the previous corneal refractive surgery patient

Cataract surgery in cases with previous corneal refractive surgery may be a major challenge for the ophthalmologist. The refractive outcome of the case deserves special attention in the preoperative planning process, which should be tailored for the type of prior refractive procedure: incisional, ablative under a flap, or on the corneal surface. Avoiding refractive surprise after cataract surgery in these cases is principally dependent on the accuracy of the intraocular lens calculation, together with the selection of the appropriate biometric formula for each case. Modern techniques for cataract surgery help surgeons to move toward the goal of cataract surgery as a refractive procedure free from refractive error. We give practical guidelines for the cataract surgeon in the management of these challenging cases.

Analysis of the biocompatibility of perfluoropolyether dimethacrylate network using an organotypic method

In this work, we have investigated the potential of perfluoropolyether (PFPE) polymers for use in biomaterial applications, especially in cell culture and tissue engineering. PFPE substrates were synthesized by the photocuring of liquid PFPE urethane dimethacrylate. These surfaces were then modified by ECM protein coatings and microstructuration, to promote cell adhesion and migration. The surface properties of PFPE and PDMS (used as a reference) samples were studied by static contact angle measurements and AFM imaging. Both polymer surfaces were hydrophobic, having sessile air-water contact angles superior to 100°. Collagen and fibronectin coatings were found to change the wettability of PFPE and PDMS samples. The biological testing of substrates was done using a liver organotypic culture to evaluate the migration and density of liver cells. The results over seven days of culture demonstrated that the migration and density of cells cultured under untreated PFPE were higher than the migration and density of cells cultured under PDMS. ECM protein coatings enhanced cell migration from liver explants cultured on PFPE or PDMS. Furthermore, these coatings were more efficient in the case of a PFPE sample. From a second series of tests, in which the PFPE was microstructured, it was found that microstructures promoted the formation of a 3D cell layer. These results indicate that PFPE polymers have a potential for use in the development of biomaterials for tissue engineering and cell culture.

Intracorneal Inlays for the Correction of Ametropias

Various materials have been placed in the corneal stroma to modify a spherical refractive error (usually hyperopic). As the surgical procedures evolved to simplify the insertion process so has the quality and biocompatibility of the implanted materials. Failures have been due to excessive inlay dimensions, bioincompatibility of the materials used, poor choice of test model, or combinations of the above. We present a thorough analysis of the history of the intracorneal inlay and the materials and techniques used up to and including the current materials and techniques available for the correction of spherical refractive errors.

Histological and confocal changes in rabbit cornea produced by an intrastromal inlay made of hexafocon A

PURPOSE

The aim of this study was to evaluate biocompatibility of a newly proposed intrastromal inlay in rabbit corneas.

METHODS

Eighteen eyes of 9 New Zealand rabbits were included in this prospective study. An intrastromal pocket was created in both eyes using Melles instruments. Annular intracorneal inlays made of hexafocon A were implanted randomly into the stromal pocket of one eye of each rabbit. Confocal microscopy was performed at each visit during 6-month follow-up. After 6 months, the rabbits were killed and corneal tissues of both eyes were sent for light microscopic studies.

RESULTS

Mild stromal edema was present during the first few days and disappeared afterward with mild haze around the tunnel site in all cases. Deposits around the lamellar channel developed in 3 implanted eyes and in none of the pocket-only eyes. No neovascularization or epithelial downgrowth was present at the incision site in any case. All inlays remained centered and optically clear. In confocal imaging, we observed no significant difference in keratocyte cell density and inflammatory cells between the control pocket-only group and inlay group. In pathological evaluation, there was no difference in the average epithelial thickness between both groups. Descemet membrane and endothelium appeared normal in both groups.

CONCLUSIONS

This study revealed safety and biocompatibility of hexafocon A as an intracorneal inlay in rabbits.

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.

Developments in the correction of presbyopia II: surgical approaches

PURPOSE

To discuss the various static and dynamic surgical approaches which attempt to give presbyopes good vision at far, intermediate and near viewing distances.

CONTENT

Static methods broadly adopt the same optical techniques as those used in presbyopic contact lens correction and aim to satisfy the needs of the presbyope by increasing binocular depth-of-focus, often using monovision as well as simultaneous-imagery. Dynamic methods generally attempt to make use of at least some of the still-active elements of the accommodation system. They include procedures which are supposed to modify the relative geometry of the ciliary muscle and lens, or which reduce the stiffness of the presbyopic lens either by replacing it with other natural or man-made material or by subjecting it to femtosecond laser treatment. Alternatively the natural lens may be replaced by some form of intraocular lens which changes power as a result of forces derived from the still-active ciliary muscle, zonule and capsule, or other sources.

CONCLUSIONS

At present, multifocal intraocular lenses appear to offer the most consistent and reliable surgical approach to surgical presbyopic correction. They have obvious advantages in convenience and stability over optically-similar, simultaneous-image presbyopic contact lenses but this must be balanced against their relative inflexibility in cases of patient dissatisfaction. Dynamic methods remain largely experimental. Although some approaches show promise, as yet no method has demonstrated a reliable, long-term ability to correct distance refractive error and to appropriately change ocular power in response to changes in viewing distance over the normal range of interest.

Preoperative topographic characteristics of eyes that developed postoperative LASIK keratectasia

PURPOSE

To assess the suitability of corneal anterior and posterior surface aberrations and pachymetry profile data to discriminate between eyes that later developed postoperative LASIK iatrogenic keratectasia and eyes that remained stable.

METHODS

Ten eyes of five patients that later developed iatrogenic keratectasia and 245 control eyes of 245 patients with a stable postoperative LASIK follow-up of 12 months or more were included. Zernike coefficients from anterior and posterior cornea, data from corneal pachymetry profiles, and output values of discriminant functions (input from Zernike coefficients, pachymetry data, and age) were assessed for their usefulness to discriminate between preoperative eyes with iatrogenic keratectasia eyes and controls using receiver operator characteristic (ROC) curve analysis. Furthermore, Randleman Ectasia Risk Scores were calculated for each eye.

RESULTS

Anterior horizontal coma (C3(1)) was the coefficient with highest discriminative ability (area under the ROC curve [AZROC] = 0.819). For posterior coefficients and pachymetry data, AZROC values were lower. Constructing discriminant functions increased AZROC values. The function containing anterior and posterior Zernike coefficients, pachymetry data, and age reached an AZROC of 0.991. The other functions ranged from 0.858 (pachymetry) to 0.981 (anterior and posterior Zernike coefficients and age). With the Randleman Ectasia Risk Scores, 80.4% were classified correctly if eyes with 4 points or more were excluded from treatment (87.1% for 3 points or more).

CONCLUSIONS

Preoperative corneal topographic characteristics of eyes that developed iatrogenic keratectasia were different than those of eyes that remained stable. However, topography patterns were not identical with those found in eyes with subclinical keratoconus in previous studies. Discriminant functions from Zernike coefficients and pachymetry data were useful to discriminate between normal eyes and eyes with preoperative iatrogenic keratectasia.

Removability of a small aperture intracorneal inlay for presbyopia correction

PURPOSE

To evaluate the safety of the corneal inlay removal procedure and the reversibility of visual acuities, corneal topography, and corneal biomicroscopy changes in a series of cases.

METHODS

Ten cases implanted with one of three versions of the AcuFocus Kamra Inlay (ACI 7000, 7000T, and 7000PDT; AcuFocus, Inc., Irvine, CA) were followed for a minimum of 6 months after corneal inlay removal.

RESULTS

The reason for removal was related to subjective dissatisfaction with visual symptoms (8 of 10 patients) such as night glare, photophobia, starburst, blurry vision, and halos. One case of removal was related to inadvertent thin flap and the final case was related to insufficient near vision. Mean uncorrected distance visual acuity (UDVA) and uncorrected near visual acuity (UNVA) was 0 ± 0.1 logMAR (Snellen 20/20) and 0.5 ± 0.2 logMAR (Snellen 20/40), respectively, preoperatively and 0.1 ± 0.1 logMAR (Snellen 20/25) and 0.5 ± 0.1 logMAR (Snellen 20/63), respectively, 6 months after corneal inlay removal. Mean corrected distance visual acuity (CDVA) and corrected near visual acuity (CNVA) was 0 ± 0.1 logMAR (Snellen 20/20) and 0 ± 0.1 logMAR (Snellen 20/20), respectively, preoperatively and 0 ± 0.1 logMAR (Snellen 20/20) and 0.1 ± 0.1 logMAR (Snellen 20/25), respectively, 6 months after corneal inlay removal. Mean root mean square (RMS) higher-order aberration (HOA) was 0.50 ± 0.12 (range: 0.30 to 0.70) preoperatively and 0.69 ± 0.14 (range: 0.48 to 0.95) 6 months after corneal inlay removal (P < .8). Weak positive correlation was found between Δt Implant-Removal (Δt I-R), RMS spherical, coma, and HOA at 6 months (Δt I-R vs RMS spherical was r = 0.2, r(2) = 0.5, P < .7; Δt I-R vs RMS coma was r = 0.8, r(2) = 0.6, P < .3; and Δt I-R vs HOA r = 0.8; r(2) = 0.6, P < .9).

CONCLUSION

This study suggests that after removal of the corneal inlay, corneal topography and corneal aberrometry are not permanently affected. In more than 60% of patients, CNVA, CDVA, UNVA, and UDVA were similar to the preoperative value.

In vivo biocompatibility of two PEG/PAA interpenetrating polymer networks as corneal inlays following deep stromal pocket implantation

This study compared the effects of implanting two interpenetrating polymer networks (IPNs) into rabbit corneas. The first (Implant 1) was based on PEG-diacrylate, the second (Implant 2) was based on PEG-diacrylamide. There were inserted into deep stromal pockets created using a manual surgical technique for either 3 or 6 months. The implanted corneas were compared with normal and sham-operated corneas through slit lamp observation, anterior segment optical coherence tomography, in vivo confocal scanning and histological examination. Corneas with Implant 1 (based on PEG-diacrylate) developed diffuse haze, ulcers and opacities within 3 months, while corneas with Implant 2 (based on PEG-diacrylamide) remained clear at 6 months. They also exhibited normal numbers of epithelial cell layers, without any immune cell infiltration, inflammation, oedema or neovascularisation at post-operative 6 month. Morphological studies showed transient epithelial layer thinning over the hydrogel inserted area and elevated keratocyte activity at 3 months; however, the epithelium thickness and keratocyte morphology were improved at 6 months. Implant 2 exhibited superior in vivo biocompatibility and higher optical clarity than Implant 1. PEG-diacrylamide-based IPN hydrogel is therefore a potential candidate for corneal inlays to correct refractive error.

The effect of inlay implantation on corneal thickness and radius of curvature in rabbit eyes

PURPOSE

To study the effect of inlay implantation on corneal shape, assessing the changes using optical coherence tomography (OCT) and a customized image analysis software.

METHODS

Thirteen rabbit eyes were operated on, with positive-powered corneal inlays implanted into 11 eyes and 2 eyes serving as flap-only controls. Cross-sectional OCT images were obtained using Optovue preoperatively, and 1 hour, 1 week, and 1 month postoperatively. Topography maps were obtained preoperatively using Medmont E300. Image analysis software was built to extract corneal thickness and radius of curvature. Anterior corneal radius of curvature values obtained from the OCT images were compared with the corneal topography maps to assess the validity of the method.

RESULTS

Corneal thickness increased more than predicted immediately after the implantation. However, by 1 month, it matched closer to the added thickness of the corneal inlays. An overall pattern of epithelial thinning was observed of up to 25% at 1 month. The anterior corneal surface had steepened up to 15% at 1 month, whereas inconsistent changes for the posterior corneal surface were observed.

CONCLUSIONS

After corneal inlay implantation, an immediate response was observed in the cornea. Corneal swelling because of surgical trauma was the most likely cause for the observed thickening of the cornea up to 1 week. By 1 month, the epithelial layer measured thinner for most eyes. Most of the added thickness was transferred to the central anterior corneal surface, causing steepening at 1 month. The anterior corneal radius of curvature values obtained from OCT images were in broad agreement with Medmont topography.

Short-term cell death and inflammation after intracorneal inlay implantation in rabbits

PURPOSE

To investigate the cell death and inflammatory response to insertion of the KAMRA inlay (AcuFocus Inc) for presbyopia.

METHODS

Twenty-four rabbits were included in the study. Each rabbit had pockets generated in both corneas with a femtosecond laser. One eye of each rabbit had an inlay inserted into the pocket and the opposite control eye had the pocket dissected. Eight rabbits were studied at 24 hours, 48 hours, or 6 weeks after surgery. Tissue sections were analyzed with TUNEL assay to detect cell death and immunohistochemistry for CD11b to detect monocytes as a marker of inflammation.

RESULTS

The inlay group had significantly more stromal cell death than the control group at 48 hours after surgery (P=.038). At 24 hours and 6 weeks after surgery, no significant difference was noted in stromal cell death between the inlay and control groups. Significantly more CD11b+ cells were noted in the stroma in the inlay group compared to the control group at 24 and 48 hours after surgery (P=.025 and P=.001, respectively). However, at 6 weeks after surgery, no significant difference in CD11b+ cells was observed between the control and inlay groups (P=.05).

CONCLUSIONS

Although an early increase in stromal cell death and inflammation occurred in eyes that underwent femtosecond laser pocket creation and KAMRA inlay insertion compared to a control group with the pocket only, no significant difference was noted between the inlay and control groups in stromal cell death or inflammation at 6 weeks after surgery.

A perfluoropolyether corneal inlay for the correction of refractive error

This study assessed the long-term biological response of a perfluoropolyether-based polymer developed as a corneal inlay to correct refractive error. The polymer formulation met chemical and physical specifications and was non-cytotoxic when tested using standard in vitro techniques. It was cast into small microporous membranes that were implanted as inlays into corneas of rabbits (n = 5) and unsighted humans (n = 5 + 1 surgical control) which were monitored for up to 23 and 48 months respectively. Overall, the inlays were well tolerated during study period with the corneas remaining clear and holding a normal tear film and with no increased vascularisation or redness recorded. Inlays in three human corneas continued past 48 months without sequelae. Inlays in two human corneas were removed early due to small, focal erosions developing 5 and 24 months post-implantation. Polymer inlays maintained their integrity and corneal position for the study duration although the optical clarity of the inlays reduced slowly with time. Inlays induced corneal curvature changes in human subjects that showed stability with time and the refractive effect was reversed when the inlay was removed. Outcomes showed the potential of a perfluoropolyether inlay as a biologically acceptable corneal implant with which to provide stable correction of refractive error.

Refractive surgical correction of presbyopia with the AcuFocus small aperture corneal inlay: two-year follow-up

PURPOSE

To evaluate the safety and efficacy of the AcuFocus Corneal Inlay 7000 (ACI 7000) implanted in emmetropic presbyopic patients for the improvement of near and intermediate vision over 2-year follow-up.

METHODS

This prospective, non-randomized, non-comparative study included 32 naturally emmetropic presbyopic patients. The intracorneal inlay was implanted in the non-dominant eye over the pupil by creating a superior-hinged flap with the IntraLase 60-kHz femtosecond laser (Abbott Medical Optics). Inlay centration was over the line of sight. Minimum postoperative follow-up was 24 months.

RESULTS

After mean follow-up of 24.2±0.8 months (range: 24 to 26 months), 96.9% of patients read J3 or better in the implanted eye. Mean binocular uncorrected near visual acuity improved from J6 preoperatively to J1 after 24 months. Mean binocular uncorrected intermediate visual acuity (UIVA) was 20/20 at 1 month and remained 20/20 throughout 24-month follow-up, with 71.9% of eyes reaching UIVA of 20/20 or better. At 24 months, mean uncorrected distance visual acuity was 20/20 in the implanted eye and 20/16 binocularly. No inlay was explanted during the study. Two decentered inlays were recentered after 6 months because of in-sufficient increase in near and intermediate visual acuity. Both patients' near and intermediate visual acuity improved significantly after recentration.

CONCLUSIONS

The ACI 7000 seems to provide a safe and effective treatment for presbyopia over follow-up of 2 years.

Development of hydrogel-based keratoprostheses: a materials perspective

Research and development of artificial corneas (keratoprostheses) in recent years have evolved from the use of rigid hydrophobic materials such as plastics and rubbers to hydrophilic, water-swollen hydrogels engineered to support not only peripheral tissue integration but also glucose diffusion and surface epithelialization. The advent of the AlphaCor core-and-skirt hydrogel keratoprosthesis has paved the way for a host of new approaches based on hydrogels and other soft materials that encompass a variety of materials preparation strategies, from synthetic homopolymers and copolymers to collagen-based bio-copolymers and, finally, interpenetrating polymer networks. Each approach represents a unique strategy toward the same goal: to develop a new hydrogel that mimics the important properties of natural donor corneas. We provide a critical review of these approaches from a materials perspective and discuss recent experimental results. While formidable technical hurdles still need to be overcome, the rapid progress that has been made by investigators with these approaches is indicative that a synthetic donor cornea capable of surface epithelialization is now closer to becoming a clinical reality.