1. The Use of a PMMA Keratoprosthesis in Severe Ocular Chemical Burn Fabiano Cade, Allyson Tauber, Claes H. Dohlman Massachusetts Eye and Ear Infirmary Harvard Medical School Boston, MA, USA The authors have no financial interest.

2. Introduction Ocular chemical burns are often devastating injuries that cause vision loss and structural damage to both the ocular surface and internal ocular tissues; (1,2) Visual prognosis often depends on the degree of ocular surface damage; (2) Strategies for vision rehabilitation after severe ocular chemical burns remain a challenge. The impact of stem cell loss on long- term corneal graft survival is a problem; (3,4)

3. Purpose To evaluate the outcomes of the Boston Keratoprosthesis (BKPro) after severe ocular chemical burns; Methods A retrospective review of charts was performed on all 24 patients (29 eyes) with severe chemical burns who underwent BKPro surgery at the Massachusetts Eye & Ear Infirmary between 1990 and 2008. We analyzed preoperative and postoperative parameters such as the type of chemical burns, number of BKPro surgeries, visual acuity and complications.

4. Results The 24 patients (29 eyes) in this study were followed for a mean of 57 months (range 1-162 months).; Sixteen eyes had an alkaline burn, 12 an acidic burn and one eye was not possible to identify the type of chemical burn; Twenty-two eyes retained their initial BKPro throughout the follow-up course and seven eyes required repeat BKPro surgeries. Reasons for BKPro replacement were either varying degree of stromal melting in seven eyes or skin overgrowth on the BKPro type II optical surface (one eye);

5. Results Preoperative visual acuity was counting fingers or worse in all eyes. Fifteen eyes (52%) achieved 20/50 or better VA at some point during their follow-up, but only seven (24%) maintained 20/50 at the last follow-up (Figure 1);

6. Results A Kaplan-Meier survival analysis was performed to evaluate the patients who retained VA of 20/200 or better at their last follow-up (Figure 2);

7. Results The number of eyes with a preoperative history of glaucoma was 21 (72%), and three more eyes developed glaucoma postoperatively (table 1); Number of eyes Pre-BKPro glaucoma21 (of those, severe progression)(8) Additional post-BKPro glaucoma (de novo)3 No glaucoma5 Table 1. Glaucoma in BKPro operated chemical burn eyes. Pre-BKPro glaucoma was diagnosed by signs immediately post BKPro surgery or when optic nerve obscured, by firm history.

8. Results Postoperatively, a retroprosthetic membrane (RPM) developed in 12 eyes (41%), and retinal detachment (RD) in eight (27%). Fungal endophthalmitis occurred in one eye but was cured by medical therapy. Other complications in lower numbers are enumerated in Table 2. N% RPM 1241 New retinal detachment 827 Skin overgrowth 621 Leak 517 Hypotony 414 Melt 414 Device extrusion 27 Back plate loosening 27 Maculopathy 27 Phthisis † 27 Vitritis 27 Keratitis 27 Choroidal detachement 27 Suprachoridal hemorrhage 13 Endophthalmitis (fungal-cured) 13 Vitrous hemorrhage 13 N = number of eyes; RPM = retroprosthetic membrane; † Phthisis without combination with retinal detachment; some patients had more than one complication; Table 2. Post-BKPro complications beyond glaucoma.

9. Discussion This study shows that a BKPro can give excellent visual acuity (VA) after surgery, even in very severe corneal burns ; However, during follow up (here up to 5 years) there was a gradual VA decline. In cohorts of BKPros done in relatively non inflamed graft failures, a lesser VA decline is usually seen ; (5) There was a remarkable difference between the latest recorded VA regarding patients with Alkali and Acid burns. Generally, alkali penetrates deeper than acids and the well-known difference in visual outcome after types of burns is confirmed here; (2)

10. Discussion The most important preventable problem is glaucoma; 21 out of 29 had advanced glaucoma damage with optic nerve cupping already at the time of the BKPro implantation. Thus, aggravation of pre-existing glaucoma after surgery as well as de novo appearance of elevated pressure in other cases are all difficult to control; Due to the frequency of glaucoma in chemical burns, before and after KPro, glaucoma drainage devices and cyclophotocoagulation should be considered as soon as glaucoma medication fails to maintain pressure in the mid- teens;

11. Discussion Although RPM formation was the most frequent postoperative complication seen after BKPro, it was successful treatable with YAG Laser; RD was the main severe complication within one year after BKPro implantation in this cohort. However, out of the 8 RD patients, three had previously presented bad vision due to endstage of glaucoma.

12. Conclusion The advent of a KPro with high degree of retention has changed the treatment of severely burned corneas. However, restoration of clear media in many such cases has revealed further problems, particularly glaucoma. Prevention of glaucoma after burns must now be given top priority. References 1. Pfister RR. Chemical injuries of the eye. Ophthalmology, 1983. 90(10):1246-53. 2.Wagoner MD. Chemical injuries of the eye: current concepts in pathophysiology and therapy. Surv Ophthalmol, 1997. 41(4): 275-313. 3.Schrage NF, Langefeld S, Zschocke J, Kuckelkorn R, Redbrake C, Reim M. Eye burns: an emergency and continuing problem. Burns, 2000. 26(8):689-99. 4.Tuft SJ, Shortt AJ. Surgical rehabilitation following severe ocular burns. Eye (Lond), 2009. 23(10): p. 1966-71. 5.Yaghouti F, Nouri M, Abad JC, Power WJ, Doane MG, Dohlman CH. Keratoprosthesis: preoperative prognostic categories. Cornea, 2001. 20(1):19-23.