Abstract
Purpose
To report the outcomes on the Boston Type 1 Keratoprosthesis at our institution.
Design
Retrospective analysis case series.
Participants
We analyzed 54 eyes of 53 patients who previously underwent Boston Type 1 Keratoprosthesis surgery at our institution from July 2006 to March 2011.
Methods
Preoperative and postoperative parameters were collected and analyzed.
Main outcome measures
Visual acuity and keratoprosthesis stability.
Results
Common preoperative diagnoses were penetrating keratoplasty failure in 49 eyes (90.7%), chronic keratitis in 2 eyes (3.7%), ocular cicatricial pemphigoid in 1 eye (1.85%), Stevens Johnson syndrome in 1 eye (1.85%) and corneal vascularization in 1 eye (1.85%). Additionally, 40 eyes (74%) had preoperative glaucoma, and an Ahmed valve was implanted in 55% of them. Preoperative BCVA ranged from 20/200 to light perception. At an average follow-up of 20.15 months ± 12.7 (range, 1–56), postoperative vision improved to ⩾20/200 in 18 eyes (33.3%) and ⩾20/50 in 4 eyes (7.4%). The graft retention was 96%.
Conclusions
The Boston Type 1 keratoprosthesis is a valid option for high-risk patients. The design improvements in the Boston keratoprosthesis, as well as the daily implementation of the therapeutic methods, have notably diminished occurrence of the most serious complications, such as corneal necrosis and endophthalmitis. As such, glaucoma and its subsequent complications now stand as the most prevalent prognostic factor in the long term.
Keywords: Boston Type 1 Keratoprosthesis, Visual acuity, Ocular cicatricial pemphigoid, Stevens Johnson syndrome, Corneal necrosis, Instituto de Microcirugía Ocular IMO
1. Introduction
Since 1789, when the French surgeon Guillame Pellier de Quengsy first described a corneal prosthesis Pellier de Quengsy, xxxx, there have been numerous attempts to design a keratoprosthesis which fulfills the criteria of biocompatibility and long term retention, with good visual acuity according to both patient and ophthalmologist; and which does not call for complex techniques (Barber, 1988). As a result of the multiple possible complications and the high extrusion rate, the keratoprosthesis is used only exceptionally. However, recent years have seen the search for the ideal prototype intensify, due in part to the high level of graft rejection in high risk patients (Dandona et al., 1997), the ever growing number of patients with severe corneal pathology and the lack of donor tissue.
Moreover, graft failure has become the most widespread cause of keratoprosthesis indication. Previous studies have demonstrated that the mean survival periods of the repeated transplants decreased gradually with the number of regrafting procedures (Bersudsky et al., 2001). On the other hand, previous group found that the survival of first time grafts was 90% at 5 years and 82% at 10 years. Initial regrafts had significantly lower 5-year and 10-year survival rates, 53% and 41%, respectively. The highest survival rates were noted in primary grafts for eyes with a preoperative diagnosis of keratoconus or Fuchs’ dystrophy (Thompson et al., 2003).
At present, two keratoprostheses are generally accepted by the ophthalmothologic community; the Boston Type 1 keratoprosthesis and the Osteo-Odonto-keratoprosthesis (OOKP). Both provide acceptable retention levels and good visual results (Zerbe et al., 2006; Falcinelli et al., 2005). However, the complexity of the technique required for the implantation of the latter has led to an exponential increase in the use of the Boston keratoprosthesis in recent years. In 2002, less that 100 Boston devices were implanted worldwide, while in 2009 about 1200 procedures were reported.
Improvements and modifications in post-operational therapy have contributed to this increase (Khan et al., 2007). These design improvements include: the incorporation of a titanium ring to prevent the intraocular disassembly of the device, the addition of holes in the posterior plate, improving the diffusion of nutrients to the graft, a simplification of the assembly procedure which also causes less damage to the donor endothelium and more recently, a new titanium back plate, which is hoped to improve biocompatibility and retention levels, minimize the damage caused to the corneal tissue, and reduce the formation of retroprosthetic membranes and stromal necrosis.
Furthermore, the use and regular replacement of a contact lens (Dohlman et al., 2002), as well as the chronic administration of broad-spectrum antibiotics (Durand and Dohlman, 2009) specially Vancomicyne (14 mg/ml) (and of antifungals where necessary) have minimized the occurrence of the most serious complications such as stromal necrosis (Fig. 1) and endophthalmitis.
Figure 1.
The arrow shows initial necrosis: FP = Front Part, C = Cornea, BP = Back Plate.
2. Methods
We undertook a retrospective analysis of 54 eyes of 53 patients who underwent Boston Type 1 keratoprosthesis. We included all Boston Type 1 keratoprosthesis implantations performed at the Instituto de Microcirugía Ocular (IMO) by two surgeons (J.L.G–O.G), over a 5 year period (July 2006–March 2011).
Different demographic data, preoperative diagnoses, associated pathologies and concomitant surgical procedures were recorded. The pre and postoperative BCVA were obtained at each examination, and were measured using a Snellen chart. All the parameters were registered in an electronic database for later analysis.
3. Results
3.1. Patient demographic
The average length of the follow-up was 20.15 month ± 12.7 (range 1–56). Sixty-one (61%) of the subjects were male and Thirty-nine (39%) were female. The average age was 58.96 ± 20.35 (range 12–90).
The preoperative diagnoses were penetrating keratoplasty failure in 49 eyes (90.7%), chronic keratitis in 2 eyes (3.7%), ocular cicatricial pemphigoid in 1 eye (1.85%), Stevens Johnson syndrome in 1 eye (1.85%) and corneal vascularization in 1 eye (1.85%) (Table 1). On other hand, the primary diagnoses in these patients are shown in Table 2.
Table 1.
Preoperative diagnoses in patients with Boston Keratoprosthesis.
| Preoperative diagnoses | No. of eyes | % |
|---|---|---|
| Graft rejection | 49 | 90.7 |
| Cronic keratitis | 2 | 3.7 |
| Stevens Johnson syndrome | 1 | 1.85 |
| Ocular cicatricial pemphigoid | 1 | 1.85 |
| Corneal vascularization | 1 | 1.85 |
Table 2.
Primary diagnoses in patients with Boston Keratoprosthesis.
| Primary diagnoses | No. of eyes | % |
|---|---|---|
| Pseudophakic keratopathy | 11 | 20.4 |
| Aniridia | 8 | 14.8 |
| Infectious keratitis | 4 Herpes simplex | 14.8 |
| 2 Bacterial | ||
| 1 Fungal | ||
| 1 Acanthamoeba | ||
| Ocular trauma | 8 | 14.8 |
| Cronic keratitis | 4 Rosacea | 11.1 |
| 2 Others | ||
| Fuchs’ dystrophy | 2 | 3.7 |
| Congenital cataracts | 2 | 3.7 |
| Glaucoma | 2 Cronic | 5.5 |
| 1 Congenital | ||
| Nanophthalmos | 2 | 3.7 |
| Chemical injury | 1 | 1.85 |
| Keratoconus | 1 | 1.85 |
| Stevens Johnson syndrome | 1 | 1.85 |
| Ocular cicatricial pemphigoid | 1 | 1.85 |
The preoperative BCVA was 0.015 ± 0.028 (range light perception to 0.1) (Table 3).
Table 3.
Preoperative versus postoperative BCVA in patients with Boston keratoprosthesis.
| BCVA | Preoperative |
Postoperative |
||
|---|---|---|---|---|
| No. of eyes | % | No. of eyes | % | |
| ⩾20/20 | – | – | – | – |
| 20/25 | – | – | 1 | 1.85 |
| 20/30 | – | – | 1 | 1.85 |
| 20/40 | – | – | 1 | 1.85 |
| 20/50 | – | – | 1 | 1.85 |
| 20/60 | – | – | 1 | 1.85 |
| 20/70 | – | – | – | – |
| 20/80 | – | – | – | – |
| 20/100 | – | – | 7 | 13 |
| 20/200 | 4 | 7.4 | 6 | 11.1 |
| 20/400 | 2 | 3.7 | 5 | 9.3 |
| CF | 7 | 13 | 9 | 16.7 |
| HM | 30 | 55.6 | 10 | 18.5 |
| LP | 8 | 14.8 | 9 | 16.6 |
| NLP | 3 | 5.5 | 3 | 5.5 |
CF = counting fingers, HM = hand movements, LP = light perception, NLP = no light perception.
3.2. Intraoperative variables
Of the keratoprostheses implanted, 72.2% were aphakic models, and 27.8% were pseudophakic. The concomitant surgical procedures were as follows: Ahmed valve implanted in 22 eyes (40.7%), posterior vitrectomy in 27 eyes (50%), an IOL explant in 5 eyes (9.3%), and cataract extraction in 1 eye (1.85%).
3.3. Visual acuity outcome
The postoperative BCVA was 0.097 ± 0.18. Thirty-three (33%) achieved a BCVA ⩾ 0.1 (18 eyes) and 7.4% achieved ⩾ 0.4 (4 eyes) (Table 2). A rapid improvement in the BCVA was observed. The measurements obtained 3 months after the operation do not differ significantly from the final BCVA.
3.4. Keratoprosthesis and glaucoma
Concomitant glaucoma was present in 74% (40 eyes). An Ahmed valve was implanted in 55% of these patients (22 eyes). 59.1% of these devices (13 eyes) were implanted in the anterior chamber, and the remaining 40.9% (9 eyes) in the posterior chamber. 64.8% of the glaucomal patients required one or more medications in order to control glaucoma, but this percentage increased to 77.3% in patients with a valve implant (Table 4).
Table 4.
Medications used in patients with Boston Type 1 Keratoprosthesis.
| No. medications |
||||
|---|---|---|---|---|
| 0 | 1 | 2 | 3 | |
| Total of patients (54) | 19 | 12 | 14 | 9 |
| Patients with glaucoma (40) | 5 | 12 | 14 | 9 |
| Patients with valve (22) | 5 | 3 | 9 | 5 |
The BCVA found in the group of glaucomal patients was from 0.11 ± 0.19, and in patients with valve implants it was from 0.087 ± 0.11. The group with the tube implanted in the anterior chamber obtained a better postoperative BCVA than the group with the implant in the posterior chamber (0.12 v/s 0.04); however, the former group also presented a better preoperative BCVA (0.029 v/s 0.009). After the implantation of the keratoprosthesis, ocular pressure was monitored digitally (Rubinfeld et al., 1998), finding a mere 5.5% (3 cases) with high levels of tension (Table 5).
Table 5.
Digital pressure in patients with Boston Type 1 Keratoprosthesis.
| Digital pressure | Without valve |
With valve |
||
|---|---|---|---|---|
| N | % | N | % | |
| High | 3 | 5.5 | – | – |
| Normal-high | 2 | 3.7 | 7 | 13 |
| Normal | 18 | 33.3 | 7 | 13 |
| Normal-low | 2 | 3.7 | 5 | 9.3 |
| Low | 7 | 13 | 3 | 5.5 |
4. Discussion
The Boston keratoprosthesis was developed to be implanted in patients who were not suitable candidates for a traditional corneal transplant (Figs. 2 and 3). After implantation, the Boston keratoprosthesis has demonstrated the capacity for rapid visual recuperation (Dunlap et al., 2010). However, its long-term stability is in question.
Figure 2.
Stevens Johnson syndrome–preoperative.
Figure 3.
The same patient, 17 months after surgery.
4.1. Visual acuity outcomes
Our study group is constituted of patients with very limited visual acuity (preoperative BCVA was ⩽0.1 in 100% of eyes and ⩽0.05 in 93% of cases) and, most of them, with a limited potential maximal VA. Moreover, 74% of patients presented with preoperative glaucoma. These figures are comparable to the Multicenter Boston Type 1 Keratoprosthesis Study (Zerbe et al., 2006) (94% with preoperative visual acuity 20/400, 52% with preoperative glaucoma) and to the series by Aldaveetal (Aldave et al., 2009) (90% with preoperative visual acuity 20/400, 76% with preoperative glaucoma), and Chew et al. (2009) (86% with preoperative visual acuity 20/400, preoperative glaucoma in 73%). The majority of patients experienced a rapid visual improvement after receiving the keratoprosthesis implant. Lack of substantial improvement in most patients can be put down to concomitant glaucomal or retinal pathology.
4.2. Glaucoma and keratoprosthesis
Despite the technical limitations of intraocular pressure measurement after keratoprosthesis, we have achieved a satisfactory control of intraocular pressure. In our study group, we have just observed 5.5% of high pressure and 78% of normal or low pressure. Most of these patients have responded well to topical therapy or laser diodo cyclophotocoagulation procedure.
Given the reduced levels of the most severe complications, such as corneal necrosis and endophthalmitis, glaucoma has become the most serious challenge to patients who have received a keratoprosthesis implant. Given that the evaluation of glaucoma becomes more difficult after the implantation of a device, adequate preoperative evaluation is important. This allows for determining the necessity of a concomitant surgical procedure to manage glaucoma, which has been the case in a significant number of our patients.
Finally, we must accept that only long term close follow up of all series, will give all of us a better understanding of the real rate of long term complications and, hopefully, how to deal with them and, most important, how to work in presenting them.
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