Retroprosthetic Membrane Formation in Boston Keratoprosthesis Type 1: Incidence, Predisposing Factors, Complications, and Treatment

Incidence, risk factors, and treatment of retroprosthetic membranes following Boston keratoprosthesis eyes and the impact of glaucoma surgery

PURPOSE

To assess incidence, risk factors, and treatment of retroprosthetic membrane (RPM) formation in eyes following Boston keratoprosthesis (Kpro) implantation and their correlation with glaucoma drainage device placement (GDD).

METHODS

A retrospective review was performed on eyes that underwent Kpro type I or II implantation between 2005 and 2020 at a tertiary academic center. Multiple variables were collected including preoperative characteristics, presence of RPM, management of RPM, and outcomes including corrected visual acuity (VA). A Fischer's exact test was used to evaluate the significance of risk factors of RPM formation and an odds ratio was calculated for each possible risk factor. A Mann-Whitney U test was used to evaluate comparisons between outcomes and qualitative analyses.

RESULTS

Of the 87 eyes identified, 37 (43%) developed an RPM within an average of 1.5 years (range, 31 days-7.5 years) following Kpro implantation. Mean follow-up duration was 4.3 years. Eyes that developed RPM had significantly worse preoperative VA compared to those that did not (logMAR 2.55 vs. 2.28, p = 0.022). The mean number of prior penetrating keratoplasty procedures trended higher in eyes that developed RPM (2.46 vs. 2.18, p = 0.44) but was not significant. GDD placement after Kpro implantation was associated with an increased risk of RPM formation (RR = 1.69 p = 0.026). Of the 37 eyes that developed an RPM following Kpro, 17 (47%) were treated with Nd:YAG laser, and four of those 17 (21%) also underwent pars plana vitrectomy (PPV). Seven of 37 eyes (19%) underwent PPV without Nd:YAG. Comparisons between RPM occurrence and final VA were not significant.

CONCLUSIONS

The incidence of RPM formation following Kpro implantation was 43%. Eyes that developed RPM had significantly worse preoperative VA. GDD placement after Kpro implantation increased the risk of developing RPM. Final VA and occurrence of RPM were not significantly different between the Nd:YAG and PPV treatment groups.

Outcomes of Boston Keratoprosthesis Type I Implantation in Poland: A Retrospective Study on 118 Patients

Background: Boston Keratoprosthesis Type I (BI-KPro I) is a synthetic cornea that can be used to restore vision in patients with corneal blindness. This retrospective study evaluated the outcomes of BI-KPro implantation in 118 patients. Material: The mean age of the patients was 56.76 ± 14.24 years. Indications for keratoprosthesis implantation were as follows: graft failure, 47 (39.83%); ocular burn, 38 (32.20%); neurotrophic keratopathy, 11 (9.32%), mucous membrane pemphigoid 9 (7.67%); autoimmune, 6 (5.08%); Stevens-Johnson syndrome, 4 (3.39%); and aniridia (2.54%). Methods: The surgeries were performed between March 2019 and June 2022 at a single clinical center in two locations. The postoperative visual acuity, complications, and need for additional surgical procedures were analyzed. Results: The Best Corrected Visual Acuity before surgery was 0.01 ± 0.006. After one year (V1), it was 0.30 ± 0.27; at two years (V2), it was 0.27 ± 0.26; and at three years (V3), it was 0.21 ± 0.23. The percentage of patients with visual acuity better than 0.1 on the Snellen chart was 37.29% after 1 year, 49.35% after 2 years, and 46.81% after 3 years of follow up. The most common complications were glaucoma (78 patients; 66.1%), corneal melting (22 patients; 18.6%), and retroprosthetic membranes (20 patients; 17.0%). Conclusions: The BI-KPro can significantly improve visual acuity. The worst long-term results were obtained in the group of patients with autoimmune diseases; therefore, careful consideration should be given to implanting BI-KPro in this group. The high incidence of de novo glaucoma or the progression of pre-existing glaucoma suggests the need for careful monitoring.

[Keratoprostheses: Last Hope for the Most Severe Corneal Diseases]

Corneal blindness affects over 8 million adults and 1.5 million children worldwide, making it one of the top 5 causes of blindness. Depending on the recipient's corneal condition corneal transplantation may not be a viable treatment option. In such seemingly no-alternative situations, keratoprosthesis implantation can be an option in some patients. In terms of numbers, two types of keratoprostheses are currently used: 1. Keratoprostheses with biological haptics made of tooth or tibia bone. 2. The Boston type I-keratoprosthesis. Both types have optics made of PMMA. The most common complication is the formation of an optically disturbing retroprosthetic membrane behind the optic, which can usually be removed with YAG laser. Causes of blindness after keratoprosthesis implantation are glaucoma, endophthalmitis and retinal detachment. The extrusion rate of the Boston type I-keratoprosthesis seems to be higher than after keratoprosthesis implantation with biological haptic. Autoimmunological corneal diseases have increased extrusion rates and higher rates of endophthalmitis when compared to non-autoimmunological diseases. Visual outcomes after keratoprosthesis implantation are potentially very good and usually limited by extracorneal concomitant diseases. Advances in glaucoma diagnostic (OCT, implantation of intraocular pressure sensors), standard glaucoma prophylaxis by medication or surgery, modern retinal surgery and better treatment options in case of extrusion improve the prognosis of keratoprosthesis surgery. Still, the ideal technique for permanent anchoring of artifical optics in biological tissue has yet to be developed.

Keratoprothesen: letzte Hoffnung bei schwersten Hornhauterkrankungen

Eine Vielzahl an Hornhauterkrankungen geht mit einem hohen Versagensrisiko von Hornhauttransplantaten einher. Häufig handelt es sich um Patienten mit beidseitig hornhautbedingter Blindheit ohne Aussicht auf Besserung. In diesen, eigentlich aussichtslosen Situationen können Keratoprothesen häufig sehr schnelle und erstaunliche Sehverbesserungen erzielen, die aber mit einem hohen Risiko für schwerwiegende Komplikationen erkauft werden.