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Year : 2014  |  Volume : 2  |  Issue : 1  |  Page : 73-79

Keratoprosthesis: A review

Department of Ophthalmology, Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India

Date of Submission17-Oct-2013
Date of Acceptance17-Oct-2013
Date of Web Publication3-Dec-2013

Correspondence Address:
Rajesh Sinha
Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi
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Source of Support: None, Conflict of Interest: None

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How to cite this article:
Sinha R, Tinwala S, Shekhar H, Titiyal JS. Keratoprosthesis: A review. J Clin Ophthalmol Res 2014;2:73-9

How to cite this URL:
Sinha R, Tinwala S, Shekhar H, Titiyal JS. Keratoprosthesis: A review. J Clin Ophthalmol Res [serial online] 2014 [cited 2023 Jun 8];2:73-9. Available from: https://www.jcor.in/text.asp?2014/2/1/73/122664

Keratoprosthesis (Kpro) is performed to restore vision in patients with severe corneal blindness who are at too high a risk of graft failure after conventional corneal transplantation. Penetrating keratoplasty (PK) remains the oldest, most common, and most successful form of solid tissue transplantation. The failure rate of keratoplasty, however, is very high in patients with ocular surface disorders such as immunologically mediated cicatrizing conjunctivitis, loss of limbal cells from chemical or thermal burns, severe keratoconjunctivitis sicca, or after multiple transplant rejections and in pediatric patients. In such cases, Kpro could be an alternative and should be considered for the achievement of visual rehabilitation.

  Types/Results Top

Ciolino et al., (Ophthalmology 2013;120:1195-200) conducted a multicenter study to report the retention rate of the Boston Kro type 1 and to identify risk factors for Kpro loss in 300 eyes. Ninety-three percent of the implants were retained at their last follow-up. The probability of retention after 1 and 2 years was 94% and 89%, respectively. The reasons for Kpro loss include sterile keratolysis (9), fungal infections (8), dense retroprosthetic membranes (3), and bacterial endophthalmitis (1). Multivariate analysis demonstrated three independent risk factors for Kpro loss: Autoimmune cause, ocular surface exposure requiring a concomitant tarsorrhaphy, and number of prior failed penetrating keratoplasties.

Iakymenko et al., (Int J Ophthalmol 2013;6:375-80) presented a retrospective case series to describe the development of new types of keratoprostheses and methods of implantation. Kpro was performed in 1060 eyes of 1040 patients with leukomas of different etiology: Burns, 725 eyes (68.4%); trauma, 120 eyes (11.3%); keratitis and ocular pemphigoid, 108 eyes (10.2%); and bullous keratopathy, 107 eyes (10.1%). Visual acuity (VA) before Kpro consisted of light perception in 962 eyes (92%), and 98 eyes (8%) had minimal VA (1/200-1/50). Both eyes were blind (VA < 1/200) in 955 patients (91.8%). At the last follow-up visit VA of ≥1/200 was preserved in 806 eyes (76%).

Trichet et al., (J Fr Ophtalmol 2013;36:393-401) evaluated Alphacor Kpro in 14 eyes at high risk of corneal allograft rejection with a mean follow-up of 15.6 ± 5.6 months. Postoperative mean VA gain was 2.5 ± 3.1 lines. VA was superior or equal to 20/200 in 21% of cases. Seven cases of stromal melt (50%) occurred. Three cases (21.4%) of retroprosthetic membrane were observed and successfully managed. One patient (7.1%) developed late endophthalmitis. They concluded that Alphacor may be an alternative to corneal allograft in cases of corneal blindness at high risk of allograft failure.

Magalhaes et al., (Acta Ophthalmol 2013 Feb 14) in a prospective study reported the outcomes of Boston type I Kpro in the management of ocular burn injuries. A total of 11 Kpros were implanted in 10 eyes of 10 patients. The mean follow-up period was 25.7 ± 10.8 months. Preoperative best corrected visual acuity (BCVA) ranged from count fingers to light perception. Postoperative BCVA was better than 20/200 in 90% of the patients and better than 20/60 in 60% of the patients. The overall retention rate was 90%. The most common complications were retroprosthetic membrane formation (50%) and persistent corneal epithelial defect evolving to corneal melting (40%). Patients who underwent ocular surface procedures such as limbal transplantation prior to Kpro implantation had a lower incidence of corneal melting/thinning (P = 0.07), although this was not statistically significant.

Chan et al., (Cornea 2012;31:1128-34) identified 10 cases of infectious keratitis in a retrospective chart review of 105 patients (126 eyes) who received Kpro (7.9%). Patient diagnoses included chemical injuries (4), Stevens - Johnson syndrome (3), ocular cicatricial pemphigoid (2), and congenital aniridia (1). Kpro implantation was indicated in two eyes for a failed ocular surface and in eight for PK failure. All were on topical vancomycin and moxifloxacin for prophylaxis and two were on topical amphotericin for prophylaxis. Three infiltrates were culture negative, five were fungal (three Candida, one Fusarium, one Dactylaria constricta), and two were bacterial (Rhodococcus equi and Gram-negative cocci). Four patients had Kpro removal with therapeutic PK and 1 had Kpro replacement. At final follow-up, only two patients retained their preinfection best vision. Risk factors for infectious keratitis included a diagnosis of cicatrizing conjunctivitis (Stevens - Johnson syndrome, ocular cicatricial pemphigoid, or chemical injury) and a history of persistent epithelial defect (P = 0.0003 and 0.0142, respectively).

Aldave et al., (Ophthalmology 2012;119:1530-8) retrospectively reviewed 223 Kpro procedures performed in 205 eyes who received Boston type 1 Kpro. The most common indication for surgery was corneal graft failure (n = 50; 44%) followed by chemical injury (n = 30; 27%). Although only 2% of eyes had a preoperative corrected distance visual acuity (CDVA) of 20/20 to 20/200, 70%, 68%, and 59% of eyes had a postoperative CDVA of 20/20 to 20/200 at 6 months, 1 year, and 2 years after surgery, respectively. Ninety-one of the 113 keratoprostheses implanted (80.5%) were retained at a mean follow-up of 14.2 months. The most common postoperative complications were retroprosthetic membrane formation (27%) and sterile corneal necrosis (18%).

Koller et al., (Ophthalmologe 2012;109:454-61) retrospectively analyzed 14 patients who had undergone Boston Kpro procedure. In 13 patients the BKP was implanted after at least one PK (including three matched grafts) and in 1 patient it was performed as a primary procedure. The underlying diseases were Stevens - Johnson syndrome, chemical injury, chronic atopic dermatitis, keratoconus, granulomatous uveitis, congenital glaucoma, and eyeball injury/burn. The follow-up ranged from 1 to 21 months. Postoperative complications consisted of prolonged inflammatory anterior chamber reaction with synechia, deposits on the intraocular lens, posterior capsule opacification, secondary glaucoma, hypotension, conjunctival growth over the Kpro and cystoid macular edema. All cases had overall improvement of VA at the last follow-up visit. The maximum improvement was from counting fingers to 0.7.

Chan et al., (Cornea 2012;31:346-9) retrospectively determined the incidence, clinical features, and outcomes of infectious endophthalmitis after Boston type 1 Kpro implantation in 126 eyes. Of the three eyes developing infectious endophthalmitis, one patient had a history of congenital glaucoma, and two patients had Stevens - Johnson syndrome. The incidence of endophthalmitis was 2.4%. All patients wore a contact lens and were on vancomycin and a fourth-generation fluoroquinolone (FQ). Vitreous fluid cultures yielded Ochrobactrum anthropi, Candida parapsilosis, and Candida albicans. All patients received intravitreal amphotericin, vancomycin, and/or ceftazidime. Topical and oral antiinfective agents were tailored based on sensitivities. One patient required Kpro removal and therapeutic PK. Vision did not recover for two patients who presented with acuity of light perception only. One patient, who presented with decreased vision of 20/400, recovered to 20/60.

Robert et al., (Cornea 2012;31:339-45) evaluated use of frozen versus fresh corneal donor carriers for Boston Kpro type 1 surgery. The indication for Boston Kpro was corneal graft failure in 24 eyes; 13 patients had Kpro as a primary procedure. Median preoperative VA was counting fingers (range, 20/100 to light perception) in the fresh cornea group (19 eyes) and hand motions (range, 20/150 to light perception) in the frozen cornea group (18 eyes). Median postoperative VA were 20/150 (range, 20/30 to hand motions) and 20/150 (range, 20/40 to counting fingers) in the fresh and frozen cornea groups, respectively. Inflammation and retroprosthetic membrane formation were the most common complications with similar rates between the 2 groups. The device retention rate was 100% at the end of the follow-up period. It was concluded that frozen and fresh corneal donors seem equally efficient and safe as carriers of the Boston Kpro with similar recuperation of VA and no untoward complications, such as melt, leaks, or endophthalmitis.

Patel et al., (Eye (Lond) 2012;26:418-25) retrospectively reviewed 58 eyes of 51 patients who received a Boston type 1 Kpro. The most common indication was failed PK (81.0%). Glaucoma was the most common comorbidity (75.9%). Preoperative BCVA was <20/400 in 87.9% of eyes. At last follow-up, 43.1% of eyes had a BCVA of 20/200. Retention rate was 87.9% over an average follow-up of 21.5 ± 11.4 months. Complications increased with time, with 65.5% eyes experiencing at least one event by 6 months and 75.9% by 1 year. The most common postoperative complication was retroprosthetic membrane formation (50.0%).

Tan et al., (Ocul Surf 2012;10:15-25) conducted a systematic review on the surgical outcomes and complication rates with OOKP. The most common indications for surgery were severe cases of Stevens - Johnson syndrome and thermal and chemical burns that were not amenable to other forms of surgery or had had previous surgical failure. Anatomical survival rate in all the studies was 87.8% at 5 years. The most common intraoperative complication was vitreous hemorrhage (0-52%) and the most common long-term blinding complication was glaucoma (7-47%). Endophthalmitis rates ranged from 2% to 8%. The most common repeat surgical procedure was mucosal trimming due to mucosal overgrowth at the optical cylinder and mucosal grafting for extrusion of the OOKP or mucosal ulceration. It was concluded that of the available biological and synthetic Kpro, OOKP appears to be an excellent option for the treatment of end-stage corneal disease.

De La Paz et al., (Am J Ophthalmol 2011;151:829-839) evaluated the impact of clinical factors on the long-term functional and anatomic outcomes of OOKP and tibial bone Kpro. It was seen that OOKP and tibial bone Kpro have comparable anatomic survival at 5 and 10 years of follow-up, but OOKP had a significantly better functional success than tibial bone Kpro. Among the primary diagnoses, Stevens - Johnson syndrome, chemical burn, and trachoma have generally good functional and anatomic outcomes and the least favorable prognosis is for ocular cicatricial pemphigoid. The most frequent complications were extrusion (28%), retinal detachment (16%), and uncontrolled glaucoma (11%).

Robert et al., (Can J Ophthalmol 2011;46:164-8) described the characteristics, indications, complications, and outcomes of the patients who underwent Boston type 1 Kpro surgery in 47 eyes. The indication corneal graft failure in 27 eyes; 20 eyes had Kpro as a primary procedure. Preoperative diagnoses included aniridia (34%), mechanical trauma (11%), infections (9%), surgery-related bullous keratopathy (9%), chemical burns (9%), corneal dystrophies (9%), and Stevens - Johnson syndrome (2%). A known history of glaucoma was present in 36 eyes (77%). Median preoperative CDVA was hand motion (range, 20/100 to light perception). The device retention rate was 100% at the end of the follow-up period. Postoperative complications included retroprosthetic membrane in 12 eyes (26%) and glaucoma progression in 11 eyes (23%).

Pineles et al., (Cornea 2010;29:1397-400) reported the postoperative binocular function of patients with Boston type I Kpro implantation for unilateral visual impairment in 17 patients. Six of 17 (94%) patients demonstrated binocular function. Second-degree fusion at near was demonstrated via the Worth-4-dot test in 13 of 17 (76%) patients. Third-degree fusion at near was demonstrated in 7 of 17 (41%) patients. Patients with better postoperative sensory binocular function tended to be of younger age (P = 0.05) and have better postoperative VA (P = 0.006). Five patients were found to have some degree of ocular misalignment. Overall, patients with strabismus had worse binocularity (P = 0.04). It was concluded that implantation of the Boston type I Kpro in patients with good preoperative VA in the fellow eye is associated with useful binocular function in greater than 90% of patients.

Khouri et al., (Eur J Ophthalmol 2010;20:885-91) evaluated surgical outcomes using a temporary intraoperative Kpro in patients undergoing combined pars plana vitrectomy (PPV) and PK. Twenty-four eyes underwent combined K-pro/PPV/PK (mean follow-up 36 months). At final follow-up, CDVA improved in eight (40%) eyes, remained stable in eight (40%), and worsened in four (20%). Corneal graft was clear in 18 (79%) eyes; 5 (21%) had graft failure. Retinal reattachment occurred in 22 (92%) eyes; 2 (8%) developed a localized traction retinal detachment not warranting additional surgery. Derangement in intraocular pressure (IOP) was common (13 [54%] eyes). Three eyes (13%) showed signs of phthisis preoperatively that resolved with reestablishment of normal IOP postoperatively. It was concluded that temporary KP during PPV/PKP surgery allowed surgical intervention in eyes with complex anterior and posterior segment disease.

  Unusual Indications Top

Sati et al., (BMJ Case Rep 2013;2013) reported Boston Kpro for visual rehabilitation in porphyria cutanea tarda. The CDA improved after surgery along with general photoprotective measures for the exposed parts of the body.

Cortina et al., (Cornea 2012;31:844-5) reported the use of a Boston type I Kpro as a primary procedure in a 49-year-old woman with gelatinous drop-like corneal dystrophy (GDLD) in both eyes and history of recurrent corneal opacification following multiple superficial keratectomies. BCVA was counting fingers in both eyes. A Boston type I Kpro was implanted in her left eye after optical iridectomy, extracapsular cataract extraction, and anterior vitrectomy. The surgery was uneventful and one month after surgery, BCVA improved to 20/20 and has been maintained for a period of more than 14 months.

Srinivasan et al., (Indian J Ophthalmol 2012;60:232-3) reported a promising result of staphylectomy with implantation of Boston Kpro and Ahmed glaucoma valve in a 7-month-old child with a large, congenital anterior staphyloma.

Dutta et al., (Int Ophthalmol 2012;32:77-9) reported the functional outcome of a patient who had undergone Boston Kpro type I for extensive ocular surface damage caused by latex of Euphorbia. The patient was evaluated periodically for both anatomical and visual outcome. At the end of 1-year follow-up the Kpro was well retained with a BCVA of 20/40.

Haddadin et al., (Digit J Ophthalmol 2011;17:43-5) reported Kpro in congenital hereditary endothelial dystrophy after multiple failed grafts. The patient was successfully followed for 5 years with 20/30 vision, and no glaucoma.

Basu et al., (Int Ophthalmol 2011;31:219-22) reported the short-term anatomical and functional outcomes of the Boston type 1 Kpro for severe bilaterally blinding vernal keratoconjunctivitis and Mooren's ulcer who had undergone several unsuccessful ocular surface reconstruction procedures before Kpro implantation. Kpro was retained in both eyes at 1 year postoperatively with a BCVA of 20/30 in both patients.

Colby et al., (Curr Opin Ophthalmol 2011;22:267-73) reviewed emerging indications for the Boston Kpro. They summarized that in addition to multiple failed corneal grafts, other ocular conditions for which the Boston Kpro has been used include herpetic keratitis, aniridia, autoimmune ocular disorders, and pediatric corneal opacities. Cicatricial and inflammatory ocular conditions remain the most difficult cases for Kpro.

Greiner et al., (Ophthalmology 2011;118:1543-50) evaluated 40 eyes who underwent Boston type 1 Kpro surgery. Preoperative VA ranged from 20/150 to light perception and was ≤20/400 in 38 eyes (95%). Preoperative diagnoses included failed corneal transplants (47.5%), chemical injury (25%), and aniridia (12.5%). Of 36 eyes followed for ≥1 year, 32 eyes (89%) achieved postoperative BCVA ≥20/200. End-stage glaucoma most commonly caused vision loss (7 of 13 eyes, 54%) when BCVA ≥20/200 was not retained (follow-up ≥1 year). Glaucoma drainage device (GDD) erosion occurred in 9 eyes (22.5%). Retroprosthetic membrane formed in 22 eyes (55%), 5 eyes (12.5%) developed endophthalmitis, 6 eyes (15%) developed corneal melt, 7 eyes (17.5%) underwent Kpro replacement, and 23 eyes (57.5%) required major surgery to treat postoperative complications. The initial Kpro was retained in 32 eyes (80%).

Iyer et al., (Cornea 2011;30:1083-7) analyzed the visual outcome of Boston Kpro for keratopathy in silicone oil-filled eyes. Of the eight eyes that underwent surgery, anatomic retention and visual improvement were noted in seven eyes (87.5%). Repeated corneal melt necessitated the removal of the prosthesis with corneal transplant in 1 eye. Membranectomy was performed twice for retroprosthetic membrane in 1 eye. They concluded that Boston Kpro is a viable option for visual rehabilitation in postvitrectomized eyes with a decrease in vision due to retained silicone oil-induced keratopathy.

Chan et al., (Cornea 2011;30:1105-9) presented the outcomes of Boston type I Kpro implantation in combination with PPV and silicone oil for the treatment of hypotony in 13 prephthisical eyes. Inclusion criteria for surgery were eyes with VA worse than 20/400, previous failed PK, corneal opacification, visually significant or worsening hypotony, and VA 20/200 or worse in the fellow eye. VA improved in 10 of 13 eyes (77%), remained stable in 2 of 13 eyes (15%), and decreased in 1 of 13 eyes (8%). All eyes had attached retina with no progression to phthisis bulbi.

  Femtosecond For Kpro Top

Moshirfar et al., (Clin Ophthalmol 2011;5:1017-20) described a technique of femtosecond laser-assisted preparation of donor tissue for Boston type 1 Kpro to provide accurate double punching of the donor tissue for optimized alignment in the visual axis. The technique was reproducibly performed in four donor corneas mounted in an artificial anterior chamber. They suggested that this technique can provide optically centered donor tissue with smooth trephinated edges.

  Imaging Top

Shapiro et al., (Cornea 2013;32:951-5) performed a retrospective comparative study of patients with Boston Kpro. A total of 26 eyes of 23 patients were evaluated with the spectralis anterior segment optical coherence tomography (AS-OCT). Preoperative diagnoses for Kpro surgery included failed corneal transplant (69%), chemical burn (23%), and aniridia (8%). The mean duration between the Kpro surgery and the acquisition of high-resolution AS-OCT imaging was 35.8 months. The most commonly observed finding was retroprosthetic membrane formation, which was found in 77% of Kpro eyes. In 65% of Kpro eyes, epithelium was identified behind the front plate, and in 54%, an epithelial lip was seen over the anterior surface of the Kpro front plate. In 31% of Kpro eyes, periprosthetic cysts, gaps or spaces, and thinning in the corneal carrier graft were identified. It was concluded that AS-OCT has the potential for monitoring the anatomic stability of an implanted Kpro and may also help to monitor complications. Moreover, high-resolution imaging may enhance our understanding of periprosthetic anatomy.

Garcia et al., (Cornea 2010;29:1031-5) evaluated the anatomic stability of an implanted Boston type I Kpro-donor cornea interface and assessed the presence or absence of a potential space (gap) between the Kpro front plate and donor cornea using AS-OCT. The presence of a gap would raise concerns of a possible pathway for the exchange of extraocular fluid with the anterior chamber. Fifteen eyes implanted with a Boston type I Kpro were studied by the noncontact technique of AS-OCT. Eight eyes had aphakic Kpros, and the other seven had pseudophakic implants. Images were analyzed for any possible changes in the Kpro-donor cornea. Of the 15 eyes, 2 revealed a gap between the front plate and the surface of the donor cornea. With pressure, none of the eyes, including the two with gaps, demonstrated any change in the Kpro-donor cornea interface during dynamic imaging (e.g., gaping or evidence of fluid escape along the Kpro-donor cornea borders). They concluded that the implanted Kpro-donor cornea interface seems to be stable dynamically using AS-OCT.

  Pediatric Keratoprosthesis Top

Nallasamy et al., (Semin Ophthalmol 2010;25:244-8) reported a case of pediatric Kpro and concluded that with motivated parents, a successful anatomic and functional outcome can be achieved with the Boston Kpro in children of amblyopiogenic age.

  Complications Top

Kim et al., (Ophthalmology 2013 Jun 6) evaluated 125 Kpro procedures in 110 eyes, which underwent Boston type I Kpro implantation. Twenty presumed infectious infiltrates were diagnosed in 15 eyes of 15 patients, for a rate of 0.073 infections per eye-year. The rate of culture-positive bacterial keratitis was 0.022 infections per eye-year, and the rate of culture-positive fungal keratitis was 0.015 infections per eye-year. Topical vancomycin use, topical steroid use, and contact lens wear did not increase the incidence of infectious keratitis. Prolonged vancomycin use and persistent corneal epithelial defect formation were associated with an increased risk for fungal keratitis and infectious keratitis overall. There were no cases of endophthalmitis resulting from infectious keratitis. They concluded that the observed rate of microbial keratitis suggests the need for additional topical antimicrobial prophylaxis after Kpro implantation in eyes at higher risk, such as those with persistent corneal epithelial defect formation or prolonged vancomycin use.

Robert et al., (Br J Ophthalmol 2013;97:573-7) retrospectively compared the complications leading to BCVA loss in patients with Boston Kpro type 1 and GDD and those with Kpro alone in 96 eyes; 18 eyes (19%) had Kpro and GDD while 78 eyes (81%) had Kpro only. Seven eyes (39%) with Kpro and GDD experienced vision loss due to complications such as glaucoma progression (three eyes, 22%), tube occlusion (four eyes, 22%) and choroidal haemorrhage (three eyes, 17%). Vitreous incarceration was the most common cause of tube occlusion. Vitreoretinal, glaucoma, and infectious complications caused BCVA loss in 16 eyes (21%) with Kpro alone (P = 0.13). It was concluded that glaucoma progression is a major cause of visual decline post-Kpro. However, GDD implantation should only be performed in carefully selected patients. Because of a high risk of vitreous incarceration within the tube, a complete PPV should be performed prior to GDD implantation.

Robert et al., (Ophthalmology 2013 Apr 16) evaluated 75 eyes for Microbial Colonization and Antibacterial Resistance Patterns after Boston Type 1 Kpro. Bacterial cultures were positive in 64% of Kpro eyes, 76% of PKP eyes, and 80% of control eyes. Fungal cultures were negative in all but one eye with PKP. The most common isolates were Staphylococcus epidermidis, other coagulase-negative Staphylococci, and Corynebacterium species. At least one bacterial isolate resistant to fourth-generation FQ was found in 44% of eyes with Kpro, 24% of eyes with PKP, and 8% of control eyes (P = 0.01). It was concluded that eyes with Kpro were more likely to be colonized with FQ-resistant bacteria. Chronic prophylaxis with low-dose FQ is likely responsible for this increased antibiotic resistance. Modifications to the current prophylaxis regimen may be helpful in preventing further emergence of resistant pathogens.

Sivaraman et al., (Am J Ophthalmol 2013;155:814-22) evaluated whether retro-back plate retroprosthetic membrane is correlated with risk of melt in patients with a type I Boston Kpro. AS-OCT evidence of a retro-backplate membrane was observed in 100% of eyes that melted and in 34.1% of eyes that did not (P = 0.0034). Retro-backplate membrane thickness in the melt group was 278 versus 193 μm in the nonmelt group (P = 0.025). They concluded that the retro-back plate portion of a retroprosthetic membrane is to be differentiated from the retro-optic portion seen at the slit lamp. The retro-back plate membrane, as shown by AS-OCT imaging is correlated with an increased risk of sterile keratolysis, possibly because of impedance of nutritional support from the aqueous humor.

Goldman et al., (Retina 2013;33:532-41) evaluated the postoperative posterior segment complications in eyes treated with the Boston type I Kpro. One hundred and ten keratoprostheses were implanted in 98 eyes with a mean follow-up of 28.2 months (range 6-84 months). The mean time to occurrence of any posterior segment complication was 5.6 months. After Kpro surgery, 63% of all eyes had corrected distance VA of 20/200 or better at last follow-up compared with 10% of eyes preoperatively. Thirty-eight eyes (40.9%) experienced at least one postoperative posterior segment complication, the most common of which were retinal detachment (16.9%), choroidal detachment (16.9%), and sterile vitritis (14.5%). Corrected distance VA was worse among eyes that experienced posterior segment complications compared with eyes that did not at multiple postoperative follow-up intervals (statistically significant up to 3 years) and at last follow-up (P = 0.003).

Al-Amri et al., (Middle East Afr J Ophthalmol 2012;19(2):254-7) reported a 68-year-old male who developed acute retinal necrosis (ARN) after Boston type I Kpro performed for multiple graft failures secondary to herpetic keratitis. After exclusion of other causes by laboratory workup, the patient was diagnosed with ARN most likely secondary to herpetic infection. Intravenous acyclovir and oral prednisolone were administered to the patient resulting in marked improvement in VA and regression in the size of the retinitis. The patient eventually developed choroidal detachment with light perception vision. In patients with a history of herpetic keratitis or keratouveitis, it is highly advisable to maintain prophylactic systemic antiviral treatment before and after any ocular procedure such as the Boston Kpro.

Panarelli et al., (J Glaucoma 2012 May 16) evaluated changes in the anterior chamber angle after Boston Kpro placement in 10 patients with AS-OCT. Seven of ten patients had open angles before Kpro placement. Within 4 months, four of seven patients developed angle closure. Contact between the iris and the back plate was seen in three patients. Two of the four eyes demonstrated progressive angle closure. IOP was elevated in three patients postoperatively due to the obstruction of a GDD tube (one eye) and angle closure (two eyes). Thus, after Boston Kpro surgery, patients must be carefully monitored for the onset or progression of glaucoma.

Jain et al., (Cornea 2012;31:841-3) reported two cases of fungal keratitis and endophthalmitis in patients with the type 1 Boston Kpro in India. The intraoperative and early postoperative course was uneventful. The patients presented with keratitis and endophthalmitis within a few months after surgery. Both patients had soft bandage contact lenses in place and were on maintenance low-dose topical steroids and antibiotic eye drops. Culture was positive for fungus in both the cases. Despite aggressive antifungal medical therapy and surgical management, one eye was eviscerated and the other lost potential for any useful vision. They concluded that fungal infection after Kpro surgery can be devastating, negating the extraordinary visual recovery these patients achieve immediately after surgery. Chronic use of topical corticosteroids and broad-spectrum antibiotic and bandage contact lens, although indispensable, may enhance the risk of fungal infection especially in the endemic areas like India. A prophylactic antifungal regime may be mandatory when this procedure is undertaken in fungal endemic areas to improve outcomes.

Kang et al., (Arch Ophthalmol 2012;130:1051-4) described a technique of argon laser iridoplasty after Boston Kpro as a safe and effective procedure to treat visually significant optic obstruction and as a less-invasive alternative to surgical intervention. Postoperative changes in iris configuration after Boston Kpro may occur, including iris obstruction of the Boston Kpro, limiting visual potential in otherwise successful transplants wherein this procedure may be helpful.

Ramchandran et al., (Ophthalmology 2012;119:674-81) reported the clinical characteristics of infectious endophthalmitis after Boston type I Kpro implantation in 141 adult eyes. Ten (7.1%) of 141 eyes were diagnosed and treated for bacterial endophthalmitis. Average time to endophthalmitis developing after K-Pro was 9.8 months (range: 2-25 months). Coagulase-negative Staphylococci were identified in seven eyes. In 7 of the 10 eyes, recurrent endophthalmitis developed that occurred at a mean of 4 months (range: 1-13 months) after resolution of the initial episode. It was concluded that infectious endophthalmitis after Kpro implantation has a higher incidence, delayed onset, and high risk for recurrence compared with postoperative endophthalmitis associated with more common intraocular procedures such as cataract surgery. The concurrent use of topical vancomycin is recommended because it seems to be important in reducing the incidence and recurrence of endophthalmitis and because FQ ophthalmic drops alone do not seem to be sufficient prophylaxis in these eyes.

Rudnisky et al., (Ophthalmology 2012;119:951-5) conducted a multicenter study to identify risk factors for the development of retroprosthetic membranes with Boston Kpro type 1 in 265 eyes with a mean follow-up time of 17.8 ± 14.9 months. The majority (85.4%; n = 222) had undergone an average of 2.2 ± 1.2 penetrating keratoplasties before Kpro implantation, and 38 eyes (14.6%) received a primary Kpro. The overall RPM formation rate was 31.7% (n = 84). The most significant risk factor for RPM development was infectious keratitis (as a surgical indication for Kpro surgery itself), resulting in a rate of RPM formation of 70.6%.

Dokey et al., (Am J Ophthalmol 2012;154:266-271) reported the occurrence of chronic hypotony as a complication following Boston type 1 Kpro implantation. Patients who developed chronic hypotony following Boston type 1 Kpro implantation not attributable to anatomic problems (e.g., retinal detachment, over-filtering glaucoma tube shunts, tissue necrosis with aqueous leak) or other causes were identified. Sixty-eight eyes received Kpro implantation over the study period. Six eyes experienced chronic hypotony, with a median time of 18.5 months between Kpro implantation and the onset of hypotony. The incidence of chronic hypotony was 3.7% at 1 year. Of the six eyes that developed chronic hypotony, five had a previous history of glaucoma or ocular hypertension, but only three had a glaucoma drainage implant. All eyes progressing to chronic hypotony were noted to have a retroprosthetic membrane prior to the onset of hypotony. Cox regression modeling demonstrated an increased risk of chronic hypotony in eyes with retroprosthetic membranes (P < 0.01) but no increase in risk for older patients, eyes with glaucoma drainage implants, or a previous history of multiple donor corneal transplants.

Kamyar et al., (Cornea 2012;31:134-9) evaluated outcomes of the Boston type I Kpro and associated incidence of glaucoma. Thirty-six Kpro procedures were performed in 30 eyes with a follow-up of 3-67 months. The main indication for Kpro implantation was corneal graft failure (77%). Primary Kpro procedures were performed in 23% of eyes for limbal stem cell deficiency secondary to chemical burns, aniridia, and for herpetic disease. Twenty eyes (67%) had a preoperative history of glaucoma, with eight of those eyes (40%) having undergone previous glaucoma surgery. Twenty-one eyes (70%) underwent concomitant glaucoma surgery. Postoperative increased IOP (22 mmHg or higher) was noted in 15 eyes (50%), although definite glaucoma development or progression was noted in 7 of those 15 eyes (23% of total eyes). Six patients (20%) required repeat Kpro implantation, and retro-prosthetic membranes developed in 23 eyes (77%).

Talajic et al., (Am J Ophthalmol 2012;153:267-274) reported glaucoma outcomes after Boston type 1 Kpro surgery. Glaucoma diagnosis was known before surgery in 29 patients (76%) and was diagnosed after surgery in 34 patients (89%) after a mean ± standard deviation of 16.5 ± 4.7 months of follow-up. The number of patients taking IOP-lowering medications increased from 19 (50%) before surgery to 28 (76%) after surgery (P = 0.017). Eight patients (21%) had glaucoma progression. Fifteen patients (40%) had a cup-to-disc ratio of 0.85 or more.

Utine et al., (Ocul Immunol Inflamm 2011;19:413-8) described the clinical features and outcomes of corneal melt associated with Boston type I Kpro implantation in 66 adult patients. Six patients had an underlying inflammatory ocular surface disorder. Four experienced corneal melt (6.1%) 5-42 months after the initial surgery. One patient was diagnosed with Sjögren's syndrome as a result of diagnostic work up following melt. Three patients were treated with systemic immune-modulatory therapy; two experienced fungal keratitis and subsequent endophthalmitis. Kpro associated corneal melt is uncommon and appears to occur in patients with preexisting inflammatory disorders, which might not have been previously diagnosed. Timely explantation of Kpro and replacement with donor cornea may prevent a poor outcome.

Nascimento et al., (Arq Bras Oftalmol 2011;74:127-9) described two cases of infectious keratitis in patients after Boston Type 1 Kpro implantation. The first case had the device implanted due to limbal deficiency secondary to severe dry eye who presented with a fungal infection by Aerobasidium pullulans that was successfully treated with amphotericin B eye drops. The second case had Kpro implantation due to previous corneal transplant rejection showing bacterial keratitis in the fourth postoperative month. The etiologic agent was identified as Streptococcus spp. and topical treatment with vancomycin was effective. This highlights the importance of postoperative surveillance in Boston Kpro eyes.

Qian et al., (Br J Ophthalmol 2011;95:436-7) reported delayed suprachoroidal hemorrhage following Boston Kpro in two aniridic patients.

Stacy et al., (Arch Ophthalmol 2011;129:310-6) evaluated retroprosthetic membranes in patients with the Boston type 1 Kpro. The excised membranes were studied by light microscopy with hematoxylin - eosin, periodic acid-Schiff, and toluidine blue stains. Immunohistochemical and transmission electron microscopic examination were also used. It was seen that stromal downgrowth, rather than epithelial downgrowth, was the major element of the retro-Kpro membranes in this series. Metaplastic lens epithelium also contributed to opacification of the visual axis. Further advances in prosthetic design and newer antifibroproliferative agents may reduce membrane formation.

Banitt et al., (Curr Opin Ophthalmol 2011;22:133-6) reviewed the causes and treatment of glaucoma in Boston Kpro recipients. Glaucoma exists in up to three-quarters of patients who undergo Kpro surgery. The onset or progression of glaucoma in Kpro patients should be monitored through visual field testing, direct visualization and structural imaging of the optic nerve. Although medical therapy is an option, one-half to three-quarters of Kpro recipients are surgically managed with a GDD or, less commonly, cyclophotocoagulation.

Li et al., (Am J Ophthalmol 2011;152:209-18) retrospectively evaluated long-term complications related to GDDs in patients undergoing Boston type1 Kpro surgery. Forty eyes were evaluated with an average follow-up of 33.6 months. Conjunctival breakdown occurred in association with 10 GDD implants. Associated complications included endophthalmitis, hypotony, and Kpro extrusion, with six GDDs requiring removal. Long-term BCVA was maintained better in eyes in which GDD erosions did not develop.

Cade et al., (Cornea 2011;30:1322-7) evaluated the incidence of glaucoma in eyes with severe chemical burns, before and after Kpro. The number of eyes with a preoperative history or signs of glaucoma was 21; 9 of which had glaucoma progression after Kpro implantation. In addition, two more eyes developed glaucoma postoperatively. Of the 28 eyes, 6 had the Kpro replaced once and 1 had it replaced twice.

Kanoff et al., (Cornea 2010;29:1069-71) reported a case of pigmented deposits on a type I Boston Kpro associated with the use of topical ibopamine as a treatment for hypotony. The dopamine-like agent ibopamine caused black deposits on the bandage lens and on the front plate of the Boston Kpro that resulted in reduced VA. Change to a daily disposable contact lens and regular cleaning of the Kpro front plate with diluted baby shampoo eliminated this problem.

Chak et al., (Cornea 2010;29:1169-72) prospectively reviewed Boston type I Kpro patients who received Nd:YAG treatment for RPM. The incidence of RPM was 24.1% (39 of 162 eyes). Of 26 RPM eyes receiving YAG treatment, 18 had 1 YAG treatment, 6 had multiple YAG treatments, and 2 had surgical excision despite multiple YAG treatments because of membrane thickness.

  Biomaterials Top

Dong et al., (J Biomater Appl 2013 Jun 13) evaluated an improved biofunction of titanium for Kpro by hydroxyapatite coating in rabbit eyes. Titanium framework Kpro has been commonly used in the severe corneal blindness, but the tissue melting occurred frequently around titanium. Since hydroxyapatite has been approved to possess good tissue integration characteristic, nanostructured hydroxyapatite was coated on the surface of titanium through the aerosol deposition method. The outcomes showed the coating had a grain-like surface topography and a good atomic mixed area with substrate. Therefore, their findings proved that nanostructured hydroxyapatite-titanium could not only provide an improved bond for substrate but also enhances tissue integration with implants in host.

  Prophylaxis Top

Magalhaes et al., (Cornea 2013;32:407-11) evaluated the efficacy of a prophylactic regimen of daily topical 0.5% moxifloxacin and 5% povidone-iodine (PI) in patients with Boston type I Kpro. Ten patients had their inferior conjunctival fornix sampled before the addition of topical 5% PI and were considered the control group (group 1). The inferior conjunctival fornix and the Kpro-donor cornea interface of 10 patients treated with the mentioned prophylactic regimen were analyzed (group 2). Samples from the inferior conjunctival fornix were positive for coagulase-negative Staphylococcus in three patients and for Aerobasidium pullulans in one patient in group 1. The inferior conjunctival fornix and the Kpro-donor cornea interface scrapings were positive for coagulase-negative staphylococcus in two patients and one patient, respectively, in group 2. None of the patients with culture-positive results developed keratitis or endophthalmitis during the study. It was concluded that topical 0.5% moxifloxacin associated with topical 5% PI is an effective prophylactic regimen in patients with Boston type I Kpro.


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