Synthetic keratophakia for the correction of aphakia

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.

Refractive surgery: through the looking glass

Historically, surgical procedures designed to change the refractive power of the cornea have been controversial at their inception, gaining acceptance only with time and study. From intraocular lenses to corneal remodelling with the excimer laser, and numerous procedures in between, including radial keratotomy, epikeratophakia, incisional keratotomy for astigmatism, and hydrogel and polysulfone implants, ophthalmologists have balanced the risks and benefits for their patients to produce the maximum benefit at the least cost. The present status and future potential of each of these are assessed as they appear today. There is no question that progress will continue, and that our patients will be the beneficiaries of our ongoing interest in improving older procedures and developing new techniques for the correction of refractive errors.

Corneal epithelial cell growth over tethered-protein/peptide surface-modified hydrogels

In this study, we investigated the corneal epithelial cell growth rate and adhesion to novel hydrogels with (1) extracellular matrix proteins [fibronectin, laminin, substance P, and insulin-like growth factor-1 (IGF-1)] and (2) peptide sequences [RGD and fibronectin adhesion-promoting peptide (FAP)] tethered to their surface on poly(ethylene glycol) (PEG) chains. The growth rate to confluence of primary rabbit cornea epithelial cells was compared for plain polymethacrylic acid-co-hydroxyethyl methacrylate (PHEMA/MAA) hydrogels, PHEMA/MAA hydrogels coated with extracellular matrix proteins or peptides, and PHEMA/MAA hydrogels with tethered extracellular matrix proteins or peptides on the surface. The development of focal adhesions by the epithelial cells grown on the surfaces was determined by F-actin staining. Little to no epithelial cell growth occurred on the plain hydrogel surfaces throughout the 15-day culture period. Of the coated hydrogels, only the fibronectin-coated surfaces showed a significant increase in cell growth compared to plain hydrogels (p < 0.009). However, even these surfaces reached a maximum of only 20% confluence. Laminin, fibronectin adhesion-promoting peptide (FAP), and fibronectin/laminin (1:1) tether-modified hydrogels all achieved 100% confluence by the end of the culture period, although the rates at which confluence was reached differed. F-actin staining showed that focal adhesions were formed for the laminin, FAP, and fibronectin/laminin tether-modified surfaces. The results support the hypothesis that tethering certain extracellular matrix proteins and/or peptides to the hydrogel surface enhances epithelial cell growth and adhesion, compared with that seen for protein-coated or plain hydrogel surfaces.

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.

Epikeratophakia to correct traumatic aphakia after penetrating keratoplasty

A 19-year-old man with keratoconus sustained ocular trauma and became aphakic in his operated left eye 2 months after penetrating keratoplasty. Original corneal wound repair was performed without intraocular lens implantation. Attempts to correct his aphakia with a contact lens failed when the patient became intolerant to its use. As an alternative, the patient had elective epikeratophakia. A standard 8.5 mm lenticule was placed over existing corneal graft. This operation resulted in +12.25 diopters of correction and a best corrected visual acuity of 20/25 at 30 months postoperatively. There was no sign of abnormalities at the host cornea or the transplanted lenticule. This case indicates that epikeratophakia may be successfully performed over existing corneal grafts.

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.

Keratophakia and keratomileusis: safety and effectiveness. American Academy of Ophthalmology

The purpose of the Committee on Ophthalmic Procedures Assessment is to evaluate on a scientific basis new and existing ophthalmic tests, devices, and procedures for their safety, efficacy, clinical effectiveness and appropriate uses. Evaluations include examination of available literature, epidemiological analyses when appropriate, and compilation of opinions from recognized experts and other interested parties. After appropriate review by all contributors, including legal counsel, assessments are submitted to the Academy's Board of Directors for consideration as official Academy policy.

Raman spectroscopy in the study of biocompatibility

This review deals with the application of Raman spectroscopy to the study of the biocompatibility of orthopaedic and ophthalmological materials and includes an introduction, a brief theory on the fundamental concepts of the technique, a description of the method and of the traditional and non-traditional instrumentation and a brief treatment of the surface properties of the different classes of materials. In the orthopaedic field, Raman studies on the structures of glasses, ceramic materials, carbon fibres and polymers before and after implantation are reviewed, particularly as far as structural modifications at the biomaterial-tissues interface are concerned. In the ophthalmological field, the chemical biocompatibility of hydrophobic and hydrophilic polymers for intraocular and intrastromal implants and for soft contact lenses is considered with respect to the presence of monomeric reactive centres in hydrophobic materials and the water amount in hydrophilic ones. The progress of the multichannel Raman technique for 'in-vivo' measurements is also described.

Gel injection adjustable keratoplasty

Gel injection adjustable keratoplasty (GIAK) is a new refractive surgical procedure designed for the correction of myopia by injection of a gel substance into the peripheral corneal stroma. This paper describes the GIAK technique and reports the results obtained in 21 fresh cadaveric eyes using the procedure. After a deep interlamellar canal has been dissected with a helicoid spatula surrounding the visual axis, the gel is injected under keratometric control. In the 1st group of 14 eyes, the degree of correction varied from 2.2 to 12.8 D; there was a direct relationship between the amount of gel injected and the keratometric change. In the 2nd group of 7 eyes, the adjustability of the procedure was demonstrated. Through partial extraction of the gel and subsequent modification of the corneal curvature, the previously induced keratometric changes could be reversed or altered to a specific extent. Following the initial injection of gel to a targeted flattest meridian power of 35 D, an average value of 35.8 +/- 0.5 D was achieved in these eyes. We subsequently attempted to increase the flattest meridian to 40 D by partial removal of the gel and achieved a mean value of 40.2 +/- 0.4 D. Average presurgical astigmatism of 1.497 +/- 0.737 D was reduced to a postsurgical reading of 0.941 +/- 0.590 D (P = 0.005, Student's paired t-test), indicating an autocorrection by autodistribution of the gel inside the canaliculus (Laplace's law). GIAK is a simple, inexpensive procedure designed for the correction of myopia that has the added advantage of reducing preexisting astigmatism without encroaching on the visual axis.

Radial keratotomy: 500 consecutive cases

A report on 500 consecutive eyes having radial keratotomy for myopia and myopic astigmatism is presented. Surgery was on an out-patient basis under local anaesthetic, with a follow-up of 99.2% of cases, 91.8% of the 294 patients elected to have radial keratotomy on the fellow eye. The surgical protocol was designed to minimise side effects and complications rather than maximise the reduction in myopia. 6/12 unaided vision or better was achieved by 99% of cases in the low myopia group, 91% in the middle and 41% in the high myopia group. Persistent hypermetropia of +1.00D or greater occurred in only 0.4% of cases and secondary astigmatism of 1.00D or greater in 1% of cases. Corneal perforations were minimised by single-pass incisions, but this was at the cost of lesser myopic corrections in the higher myopic group. Centering on the visual axis rather than the centre of the pupil minimised glare sensitivity. No patient developed potentially blinding complications.