Ciolino JB, Belin MW, Todani A, et al. Retention of the Boston Keratoprosthesis Type 1: Multicentre Study Results. Ophthalmology 2013; 120: 1195-1200.
In a nutshell
This study reports on a total of 300 eyes which had undergone implantation of the Boston keratoprosthesis type 1 device between January 2003 and July 2008 by 19 surgeons at 18 medical centres in USA. The mean age at time of implantation was 62.6 years and 48.1% were female. The average duration of follow-up (FU) was 17 months (range 1 week - > 6 years); 161 eyes (53.7%) had at least one year of FU and 91 eyes (30.3%) had two years. The probability of retention at one year was 94% and 89% at two years. Survival is defined as anatomic retention at the last FU.
The majority of eyes (86.2%) had experienced a failed corneal transplant. Thirty-nine eyes (13.3%) underwent primary keratoprosthesis implantation because they were at high risk of graft failure. Some patients developed failure during the study period and received a replacement; only data from the first procedure were included. Causes of failure include sterile keratolysis, fungal infections, dense retroprosthetic membranes (which occur in 30% of eyes) and bacterial endophthalmitis.
Autoimmune ocular surface disease such as ocular cicatricial pemphigoid and the Stevens-Johnson syndrome, carried the lowest retention rate. Additional simultaneous surgery such as cataract extraction and tarsorrhaphy were each associated with a shorter time
Keratoprosthesis has emerged as a viable option when a traditional PK has a poor chance of success. The Boston keratoprosthesis was initially developed at the Massachusetts Eye & Ear Infirmary and underwent a series of modifications to improve longevity. In 2006, Zerbe et al from the same group reported a 95% retention rate from 141 procedures but the study was limited by a short follow-up time of 8.5 months. The purpose of this article is to provide an update on retention over a longer follow-up period and to identify risk factors for its extrusion.
The use of an aphakic keratoprosthesis carried a double risk of failure compared to the pseudophakic implants. There were no ocular co-morbidities (ex glaucoma, dry eye syndrome, age-related macular degeneration, cataract, diabetic retinopathy) that were associated with increased time to failure. However, eyes which had undergone prior glaucoma surgery had a lower failure rate. The main independent risk factors included auto-immune disease, ocular surface exposure and the number of failed PKs.
Potential contributory factors include increased collagenase activity which produces tissue necrosis and can result in corneal perforation, hypotony, or instability, leading to extrusion of the device.
- The Boston keratoprosthesis had a retention rate of 93% at two years
- Predictors of failure were an auto-immune cause, exposure keratopathy and the number of prior failed penetrating keratoplasties
- The device seems a viable option for eyes deemed unsuitable for primary penetrating keratoplasty
- The phakic implant carries a better prognosis.
Joseph A Coleiro