Histopathologic and immunologic aspects of alphacor artificial corneal failure

Nonpenetrating Foldable Intrastromal Keratoprosthesis: A Review of the Literature

PURPOSE

To review the literature focusing on the clinical outcomes of KeraKlear (KK) (KeraMed), a foldable intrastromal keratoprosthesis.

METHODS

We searched 6 databases using 4 keywords: KeraKlear, Foldable Keratoprosthesis, Intrastromal Keratoprosthesis, and Non-penetrating Keratoprosthesis. Included studies had to be conducted in vivo on humans, published until January 3, 2023, and had to investigate the implantation of the KK. Eyes were considered at high risk of keratoprosthesis retention failure whenever there was an active inflammatory ocular surface disorder or in case of previous KK failure. We aimed at recording the postoperative complications, rate of prosthesis retention, and mean improvements in visual acuity.

RESULTS

We identified 144 publications, 6 of which (38 eyes) met the inclusion criteria. No randomized controlled trials were found, and some studies had significant limitations regarding sample size and follow-up duration. With a mean follow-up of 28 ± 18.8 months, postoperative complications of any kind occurred between 0% and 50% and 24% had an implant extrusion/needed a reoperation. The mean postoperative visual acuity improvement on the last follow-up was -0.83 ± 0.27 LogMAR, that is, -0.57 ± 0.3 for high-risk and -1.03 ± 0.25 for low-risk eyes, whereas 1 year after implantation, 50% of the prostheses were retained in the former and 81% in the latter group. None of the eyes developed glaucoma, endophthalmitis, or expulsive hemorrhages; none had to be eviscerated/enucleated.

CONCLUSIONS

Despite the limited quality and quantity of evidence, the available literature seems to suggest the KK to be a valuable tool in the treatment of complicated corneal disorders. Because in many parts of the world, the access to corneal transplantation is limited, this prosthesis could represent a valid alternative.

TNF-α Inhibitors for the Management of Intractable Corneal Melt: Report of Three Cases and Review of the Literature

OBJECTIVE

To report three consecutive cases with noninfectious corneal melting, whose disease progression could only be halted with tumor necrosis-α (TNF-α) inhibitor infusion, with a review of the relevant literature.

MATERIALS AND METHODS

Patients with toxic epidermal necrolysis, severe alkaline burn, and Sjögren syndrome had experienced severe corneal melting following penetrating keratoplasty, Boston type 1 keratoprosthesis implantation or spontaneously, respectively. Topical autologous serum eye-drops, medroxyprogesterone, and acetylcysteine formulations; frequent nonpreserved lubrication; systemic tetracyclines and vitamin-C supplements; topical and systemic steroids and steroid-sparing agents; surgical approaches including amniotic membrane transplantation, tectonic graft surgery; and tarsorraphy failed to alter the disease courses.

RESULTS

Upon consultation with the rheumatology clinic, TNF-α inhibitor infliximab (Remicade; Centocor Ortho Biotech Inc, Horsham, PA) 5 mg/kg infusion was planned for each patient. After 0-, 2-, and 6-week doses, monthly infusion at the same dose was maintained for 12 months because of severe and intractable course of their diseases. Each case showed dramatic improvements in corneal melts; and sterile vitritis in the eye with Boston keratoprosthesis responded, as well.

CONCLUSIONS

Inhibiting TNF-α-mediated expression of matrix metalloproteinases responsible for collagen breakdown should be considered in refractory cases, as a means of globe salvage.

Short-Term Clinical Outcomes of a Novel Corneal Prosthetic Device in a Rabbit Model

PURPOSE

To evaluate the clinical performance and biocompatibility of a novel synthetic corneal device.

METHODS

Synthetic, single-piece, foldable, suturable, optic-and-skirt design prototype devices were fabricated using expanded polytetrafluoroethylene. A combination of intralamellar and full-thickness penetrating techniques was used for implantation. A topical antibiotic-steroid regimen was used postoperatively. Rabbits were examined weekly using penlight and at monthly intervals under an operating microscope with integrated optical coherence tomography. Optical quality, retention, and complication rates at 3 and 6 months were assessed.

RESULTS

Nineteen rabbits underwent surgery. There were no device-related intraoperative complications. Creation of lamellar pocket was problematic in 2 younger rabbits with inadequate chamber depth. Two rabbits had early postoperative infectious keratitis attributed to bandage contact lens wear, which was ceased. Rabbits were treated using fourth-generation fluoroquinolone drops and did well over a period of 6 months without device extrusion or further complications. Four other rabbits had late postoperative infectious keratitis because of exposed suture(s), which progressed to endophthalmitis. One rabbit had sterile keratolysis and retraction of the anterior corneal lamella. There was no retinal detachment, glaucoma, anterior or posterior synechiae, or cataract formation in any of the rabbits. All devices remained in situ with clear optics without spoliation. Light microscopic examination of the globes demonstrated intact epithelium overlying the skirt and new collagen integration into the porous structure of the skirt without significant inflammation.

CONCLUSION

Our results demonstrated favorable short-term anatomical clinical outcomes of this novel synthetic corneal prosthesis. Further studies are warranted to characterize the biointegration of this device.

Corneal graft melting: a systematic review

Corneal graft melting is a severe complication of keratoplasty. This review is to summarize the incidence, the pathogenesis, the risk factors, the prognosis and the prevention of corneal graft melting after keratoplasty. We systematically searched PubMed, Web of Science and WanFang database to retrieve potentially eligible articles about relevant clinical reports and animal experiments. We read the full texts to identify eligible articles. The selection of studies and data extraction were performed independently by two reviewers. In conclusion, the pathogenesis of corneal graft melting is complicated, and many risk factors are closely related to corneal graft melting. Analysis of pathogenesis and risk factors of corneal graft melting can facilitate the development of targeted therapies to better guide clinical practice.

Infliximab after Boston Keratoprosthesis in Stevens-Johnson Syndrome: An Update

PURPOSE

To report our experience using intravenous infliximab for the treatment of tissue melt after Boston keratoprosthesis (B-KPro) types I and II in patients with autoimmune disease.

METHODS

Case series.

RESULTS

We identified four patients who were treated with intravenous infliximab in the context of tissue melt after B-KPro. Stevens-Johnson syndrome-associated corneal blindness was the primary surgical indication for B-KPro implantation in all patients. Two patients received a B-KPro type I and two patients received a B-KPro type II. The patients received intravenous infliximab for skin retraction around B-KPro type II, melting of the carrier graft or leak. Treatment resulted in a dramatic decrease in inflammation and, in some cases, arrest of the melting process. Cost and patient adherence were limiting factors to pursuing infliximab therapy. In addition, one patient developed infusion reactions.

CONCLUSIONS

Intravenous infliximab may be considered as globe- and sight-saving therapy for tissue melt after B-KPro.

Ocular surface, fornix, and eyelid rehabilitation in Boston type I keratoprosthesis patients with mucous membrane disease

PURPOSE

To understand the efficacy of various approaches for ocular surface reconstruction in eyes with implanted Boston Type I keratoprosthesis.

METHODS

All eyes implanted with a Boston Type I keratoprosthesis over a 9-year period by a single surgeon were reviewed. Any case in which mucosal rehabilitation was performed was included in the study sample. The type, number, approach, and outcome for all eyelid and ocular surface procedures were assessed.

RESULTS

A total of 22 mucosal surface surgeries were performed before, concurrent with, and after implantation of 11 keratoprostheses and 1 penetrating keratoplasty (after keratoprosthesis removal) in 9 eyes of 9 patients. Most of the ocular surface reconstructive surgeries (81.8%; 18/22) were performed at the time of or following keratoprosthesis implantation, with the most common indication being corneal stromal necrosis (44.4%; 8/18). Free grafting and simple advancement resulted in graft retraction for each case, and pedicle or bucket handle flaps resulted in a stable vascularized graft for half of the cases. Graft retraction occurred in 6 of the 9 eyes in this study, including in all 5 eyes of patients with Stevens Johnsons syndrome (SJS).

CONCLUSIONS

Free grafting and simple advancement flaps do not appear to be effective for rehabilitation in these eyes. However, even vascularized pedicle and bucket handle flaps retracted 50% of the time. Individuals with SJS were more likely to both require conjunctival rehabilitation after keratoprosthesis surgery and develop graft retraction in the course of management.

A new epidescemetic keratoprosthesis: pilot investigation and proof of concept of a new alternative solution for corneal blindness

PURPOSE

To report the outcomes of a new model of epidescemetic keratoprosthesis (Kpro) implanted without total corneal trephination.

METHODS

Patients were considered for implantation with the new Kpro model (KeraKlear) if they were at high risk of failure with standard penetrating keratoplasty (PK) or showed conditions with a poor prognosis following PK such as severe chemical injury. We used femtosecond laser to create the surgical planes adequate for the purpose of the Kpro implantation, and the Kpro was implanted intralamellar in 11 eyes and epidescemetical in 4 eyes. Follow-up was between 7 and 21 months and mainly for anatomical outcomes and complications.

RESULTS

For the intralamellar technique, the anatomical outcome was excellent in five eyes with no complications. The other six eyes developed complications such as deep corneal inflammatory membrane, totally vascularised cornea, extrusion of the Kpro and corneal melting, all of which were managed successfully. No eye was lost. For the epidescemetical technique, the anatomical outcome was excellent in all four eyes.

CONCLUSIONS

The new KeraKlear Kpro has proved to be a viable alternative to corneal transplantation with potential advantages like decreased risk of endophthalmitis, expulsive haemorrhage and worsening glaucoma. KeraKlear Kpro is better tolerated and less prone to complications when implanted epidescemetically; cases with poor corneal quality are better associated to a lamellar fenestrated donor corneal graft, leaving the posterior corneal surface intact and implanting the Kpro between.

An innovative intrastromal keratoprosthesis surgery assisted by femtosecond laser

PURPOSE

To demonstrate the surgical application of a new model of epidescemetic keratoprosthesis.

METHODS

A 53-year-old man was referred to our center with severe alkali burns in both eyes and was treated by a combined corneal graft associated with KeraKlear implantation assisted by femtosecond laser and cataract surgery with implantation of an intraocular lens.

RESULTS

After 1 month, visual acuity was 0.6 logMAR in both eyes with -2 sphere correction. Slit-lamp examination and anterior segment optical coherence tomography revealed that the device was centered in the pupil area with no infection. No sign of extrusion was detected.

CONCLUSIONS

The advantage of this device is that it involves nonperforating surgery, thus reducing the postoperative risk of infection and necrosis of tissue around the prosthesis. Large-scale studies with a long follow-up period are required to evaluate the outcome of use of this device.

Histologic evaluation of AlphaCor keratoprosthesis explanted following various complications

AIMS

To report the histological findings in two AlphaCor artificial corneas explanted following complications,to compare the mechanism of biointegration and/or failure of the device and the correlation with clinical histories.

METHODS

The first patient was diagnosed with optic deposits and corneal melting during the late postoperative period and required the removal of the device. The second patient experienced injury with penetration of the device 5 months after implantation. The explanted devices embedded within the corneal tissues were processed for pathological analysis at the John A. Moran Eye Center, University of Utah, Salt Lake City, USA. Histologic findings were compared with earlier histological results from animal studies and human case series and correlated with clinical histories.

RESULTS

Both devices demonstrated normal skirt porosity. Light microscopic examination of the specimens disclosed adequate biointegration - colonization of the peripheral skirt with cellular elements present within the pores of the skirt. In the first patient (specimen 1) epithelial ingrowth was observed between the peripheral skirt and the posterior surface of the specimen, with partial extrusion of the device in that area. In the second case (specimen 2) the central, optic component of the device was missing.

CONCLUSION

Histologic findings of the AlphaCor skirt were consistent with earlier animal studies and human cases series reports. These findings confirm the occurrence of biointegration. Epithelial ingrowth and scattered chronic mononuclear inflammatory cells were observed in the area of partial extrusion in the patient with a history of melting prior to explantation.

Corneal biomechanics and biomaterials

The ability to clearly observe one's environment in the visible spectrum provides a tremendous evolutionary advantage in most of the world's habitats. The complex optical processing system that has evolved in higher vertebrate animals gathers, focuses, detects, transduces, and interprets incoming visible light. The cornea resides at the front end of this imaging system, where it provides a clear optical aperture, substantial refractive power, and the structural stability required to protect the fragile intraocular components. Nature has resolved these simultaneous design requirements through an exceedingly clever manipulation of common extracellular-matrix structural materials (e.g., collagen and proteoglycans). In this review, we (a) examine the biophysical and optical roles of the cornea, (b) discuss increasingly popular approaches to altering its natural refractive properties with an emphasis on biomechanics, and (c) investigate the fast-rising science of corneal replacement via synthetic biomaterials. We close by considering relevant open problems that would benefit from the increased attention of bioengineers.

AlphaCor artificial cornea: clinical outcome

PURPOSE

The purpose of this study was to describe the long-term results of AlphaCor implantations, and to evaluate the main complications and risk factors.

METHODS

Retrospective analysis of preoperative and follow-up data from 15 AlphaCor implantations. Analysis of outcomes, trends, and associations was performed and compared with data from published clinical trials and a literature review.

RESULTS

The survival rate of the device at 1, 2, and 3 years was 87%, 58%, and 42%, respectively. Postoperative visual acuity ranged from hand movement to 0.8. The most significant complications were stromal melt (nine cases), optic deposition (three eyes), and retroprosthetic membrane formation (three eyes). The most common device-unrelated complication was trauma (three patients). All complications were managed without loss of the eye.

CONCLUSION

AlphaCor provides a treatment option for patients with corneal blindness in which a donor tissue graft would not succeed.