Permavision intracorneal inlay after sixteen years. Regression of initial refractive hyperopia

According to the available scientific literature, 77 patients underwent Permavision inlay worldwide, between 2004 and 2007. This study reported about the use of Permavision intracorneal inlay to increase the central corneal curvature and to correct hyperopia. A 32-year-old male patient went to the Tecnolaser Clinic Vision ® facilities for a refractive study. Preoperative refraction without cycloplegia was +6.00 D in the right eye (RE) and +4.00 in the left eye (LE). The surgery was performed for both eyes on December 2, 2003. The Carriazo-Barraquer mechanical microkeratome (Moria) was used to create a 180 μm-thick corneal flap with a diameter of 8.5 mm. After lifting the flap, the corneal inlay was placed centrally above the pupil and the flap was re-positioned. In this case report, the patient reverted to the initial refractive situation. The first refractive regression appeared at twelve-month follow-up. After sixteen years, it was found a decrease in maximum corneal curvature, an increase in mean corneal densitometry percentage, and no important changes in the central corneal thickness. In the reported case, the cornea reverted to its original shape. In the scientific literature, this is the first case report of a non-explanted Permavision inlay after sixteen years.

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.

One-year safety and efficacy results of a hydrogel inlay to improve near vision in patients with emmetropic presbyopia

PURPOSE

To conduct a feasibility study of the safety and efficacy of a corneal contouring inlay as a treatment for emmetropic presbyopia.

METHODS

The Raindrop corneal inlay (ReVision Optics, Inc., Lake Forest, CA) was implanted on the corneal stromal bed beneath a keratotomy flap in 20 nondominant eyes of 20 patients. The implant is designed to cause a change in the curvature of the overlying cornea, with a subsequent multifocal change in refractive power. Efficacy outcome was defined as at least 75% of eyes with uncorrected near visual acuity of 0.3 logMAR (20/40 Snellen) or better at 6 months. Main safety outcomes were retention of preoperative best-corrected distance visual acuity and reports of adverse events. Other outcome measures included contrast sensitivity; near, intermediate, and distance visual acuities; patient satisfaction; spectacle use; and complications.

RESULTS

All implanted eyes achieved uncorrected near visual acuity of 0.3 logMAR (20/40 Snellen) or better by the 1-week postoperative examination and remained so throughout the 1-year follow-up period, also averaging less than 0.1 logMAR (20/25 Snellen) monocularly and binocularly throughout that period. Mean binocular uncorrected distance visual acuity remained within 0.02 logMAR of the preoperative mean throughout the study. One patient who was dissatisfied with the resulting vision underwent explantation. At 1 year, 16 of 19 patients seldom or never wore glasses and all 19 were satisfied or very satisfied with their overall vision.

CONCLUSIONS

The hydrogel corneal inlay improved uncorrected near and intermediate visual acuity in patients with emmetropic presbyopia, with high patient satisfaction and little effect on distance visual acuity.

Synthetic corneal inlays

This review is based on the activities of the Vision Cooperative Research Centre (previously Cooperative Research Centre for Eye Research and Technology) Corneal Implant team from 1991 to 2007. The development of a synthetic polymer of perfluoropolyether (PFPE), meeting essential physical and biological requirements, for use as a corneal inlay is presented. Each inlay was placed in a corneal flap created with a microkeratome and monitored over a two-year period in a rabbit model. The results indicate that the PFPE implant shows excellent biocompatibility and biostability. As a result, a Phase 1 clinical trial is being conducted. Three years post-implantation, the PFPE inlays are exhibiting continued excellent biocompatibility. Corneal inlays made from PFPE are biocompatible with corneal tissue in the long term and offer a safe and biologically-acceptable alternative to other forms of refractive surgery.

The Max Schapero Memorial Award Lecture 2004: Contact Lenses on and in the Cornea, What the Eye Needs

PURPOSE

The aim of this study is to review the advances made in understanding the needs of the cornea and the way in which it responds to contact lens wear and corneal implants.

METHODS

The review is based on personal knowledge and involvement of the author and colleagues from the 1970s to 2005.

RESULTS

Development of silicone hydrogel contact lenses is presented as well as development of synthetic materials for implantation on the corneal surface (corneal onlay).

CONCLUSIONS

The future of vision correction involves developing highly porous and biocompatible lens materials. For contact lenses, a better understanding of the effects of contact lens wear on the ocular surfaces, including the tear film, and development of lens materials with greater bacterial resistance are required. For those who require new solutions to permanent vision correction, corneal onlays (implantable contact lenses) are a minimally invasive and totally reversible procedure that can be removed or replaced as visual needs change over time.

Ocular biomaterials and implants

The maintenance of vision is a key determinant of healthy ageing. This has been facilitated over recent decades by the development of a wide range of implants and biomedical devices to correct the functional deficiencies of disease, age and ocular trauma. This brief overview provides an insight into the structure of this unique organ, the major physiological functions of the component tissues and the present state of the art with respect to modern ocular implants. The review focuses primarily on the existing limitations of existing ocular biomaterials used in the fabrication of contact lenses, intraocular lenses, glaucoma filtration implants, keratoprostheses, intracorneal implants, scleral buckles and viscoelastic replacement agents. The challenge of improving ocular compatibility and ensuring the longevity of indwelling ocular devices is addressed along with the need to improve the physicochemical and mechanical properties of existing ocular biomaterials.

Advances in refractive surgery: 1975 to the present

PURPOSE

To review the major advances in the field of refractive surgery occurring over the past 25 years.

METHODS

Literature review.

RESULTS

The major developments in refractive surgery over the past 25 years are reviewed.

CONCLUSIONS

The past 25 years have witnessed great changes in refractive surgery. As a result of advancements in technology, instrumentation, and technique, we have seen improvements in the treatment of all types of ametropias. In this article, we review some of the successes and failures of the past quarter-century.

Clear Lensectomy and Intraocular Lens Implantation for Hyperopia from +7 to +14 Diopters

BACKGROUND

Our results of clear lens extraction and intraocular lens implantation to correct hyperopia from +6.75 to +13.75 D are presented, as well as evaluation of two intraocular lens calculation formulae.

METHODS

Clear lens extraction and posterior chamber intraocular lens implantation was performed in 35 normally sighted eyes of 21 patients with a mean baseline hyperopic spherical equivalent refraction of +9.19 +/- 0.34 D (range +6.75 to +13.75 D). The refractive goal was -1.50 D, using the SRK II formula in 17 eyes and the SRK-T formula in 18 eyes. Follow-up was up to 5 years.

RESULTS

Mean uncorrected visual acuity after surgery was 0.8 (range 0.5 to 1.0). Stability of refraction was noted from the second month after surgery. No eyes lost any lines of spectacle-corrected visual acuity. Using the SRK II formula, 100% of eyes were within +/-1.00 D of emmetropia and with the SRK-T formula, 83.3% for a combined 91.4% of eyes within +/-1.00 D of emmetropia. One eye required intraocular lens exchange and another eye required photorefractive keratectomy for myopia. Both procedures were necessitated by an intraocular lens miscalculation of more than +/-2.00 D. Nineteen eyes (54.2%) developed posterior capsular opacification and were treated with Nd:YAG laser capsulotomy.

CONCLUSION

Clear lens extraction is a safe, effective, and predictable procedure for the treatment of hyperopia from +6.75 to +13.75 D. The SRK II formula proved slightly superior to the SRK-T in intraocular lens calculation when using the "-1.50 D rule."

Permalens Hydrogel Intracorneal Lenses for Spherical Ametropia

PURPOSE

To assess the efficacy, stability, and safety of Permalens hydrogel intracorneal lenses for the correction of spherical ametropia 6 years after implantation.

METHODS

Implantation of intracorneal hydrogel lenses was performed by the same surgeon (JIBM) in five aphakic and five high myopic eyes. The lens closet to corneal vertex refraction was used. Refractive outcomes, keratometry, keratography, endothelial cell count, and corneal topography were studied.

RESULTS

Corneal tolerance to the hydrogel implants was maintained throughout for 6 years with no alteration in endothelial cell count. All myopic eyes showed regression of achieved correction. The aphakic eyes showed no statistically significant difference between the results at 1 month and those obtained at 1 and 6 years.

CONCLUSIONS

Hyrdogel intracorneal lenses are well tolerated and the refractive results are stable in aphakic patients. They may be considered when intraocular lenses cannot be placed in aphakic patients, but are not now in clinical use.

Preliminary Evaluation of a Hydrogel Core-and-Skirt Keratoprosthesis in the Rabbit Cornea

BACKGROUND

We developed a core-and-skirt keratoprosthesis, with both components made from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels. The identical chemical nature of both spongy skirt and transparent core assures a permanent union between them. We have previously shown that PHEMA sponges, within a certain range of pore size, can support cellular invasion and neovascularization when implanted into the rabbit cornea. The present study is the first to evaluate the behavior of the whole prosthesis after implantation into the rabbit cornea.

METHODS

Hydrogel keratoprostheses were inserted intrastromally into the corneas of seven rabbits and histologically examined by light microscopy in five eyes enucleated at 8, 12, and 14 weeks.

RESULTS

None of the implants extruded over this period. Both clinical and histopathologic examination showed that the keratoprostheses were well tolerated by the host tissue. The porous skirt was fully integrated into the stroma by fibrovascular invasion, and no capsule formed around the implants. Stromal melting anterior to the implant occurred in two cases, but this did not affect the fixation of the keratoprostheses.

CONCLUSIONS

This study indicates that our keratoprosthesis can prevent extrusion in the short term when inserted into an intrastromal pocket of the rabbit eye.

Interpenetrating polymer network (IPN) as a permanent joint between the elements of a new type of artificial cornea

The combination at the interface between two chemically identical polymers was investigated by light and electron (scanning, transmission) microscopy. The polymers constitute elements of a new type of artificial cornea in which the peripheral skirt is made from spongy poly(2-hydroxyethyl methacrylate) (PHEMA) and the central optical zone from homogeneous, transparent PHEMA. Their two-phase combination along the boundary fulfill formally the requirements for an interpenetrating polymer network (IPN). The procedure for the manufacture of prosthesis was described in detail. Thin and ultrathin sections excised from the interface region were investigated using microscopic techniques. Light microscopy allowed the measurement of the diffusion path length of transparent PHEMA into sponge, which was approximately 0.5 mm. Transmission electron microscopy revealed a cellular-like morphology as well as larger segregated zones, which indicated network interpenetration on a molecular level and also a relatively poor miscibility of the two polymers despite their identical chemical structure. The latter was interpreted as a result of the submicroscopic restraints imposed by polymer I (sponge) upon polymer II. This study provides evidence that the interface combination of the prosthetic elements should be regarded as a gradient homo-IPN. This system offers a union between elements much stronger than those previously reported in artificial corneas.

Wound healing in response to keratorefractive surgery

Over one million Americans have undergone refractive keratoplasty since the introduction of radial keratotomy into the United States in 1978. There are now a number of alternative techniques available for reshaping the corneal surface to alter ocular refractive errors. Numerous technologic advances in the past decade now enable us to perform these procedures in a safer and more reliable fashion. The ability to control precisely the refractive outcome, however, continues to elude us and appears to be limited, in part, by interindividual variability in the wound healing response. Presently, we review the corneal wound healing response to various keratorefractive approaches and suggest some interventional strategies which might enable us to modulate more precisely our refractive results.

Assessment of the long-term corneal response to hydrogel intrastromal lenses implanted in monkey eyes for up to five years

The biocompatibility of hydrogel intracorneal lenses (ICLs) implanted in monkey eyes was evaluated for periods ranging up to five years. Seventy-three plus or minus powered ICLs made of Lidofilcon A (68% water) or Lidofilcon B (79% water) were implanted following lamellar dissection with a microkeratome. Ten sham surgical procedures were performed without ICL implantation as controls. Eyes were followed for up to five years by slitlamp biomicroscopy and specular microscopy. Light and transmission electron microscopic evaluations of enucleated eyes were performed at various intervals. Minimal tissue reaction was noted; both hydrogel materials appeared to be equally well tolerated. Failures usually occurred as a result of microkeratome problems encountered during surgery. Histopathological changes to the cornea included epithelial thinning anterior to the thickest portion of the ICL, fibroblastic activity along the ICL-stromal interface, and deposition of an amorphous extracellular material adjacent to the ICL. These observations did not appear to be clinically significant as the eyes were quiet by slitlamp examination. Removal of three ICLs eight to ten months prior to enucleation restored the normal histological characteristics of the cornea. The endothelial cell density of ICL-implanted eyes decreased by 4.3% (n = 17) six months after surgery but remained stable thereafter. The variation in endothelial cell area and percentage of hexagonal cells did not change over 50 months. The results appear to demonstrate that high water content synthetic ICLs can be well tolerated in the monkey cornea for up to five years.