We read with interest the article by Li and associates that comments on the incidence of tube erosion in eyes with a Boston keratoprosthesis (KPro) and a glaucoma drainage device (GDD), covered by a soft contact lens. They found 10 conjunctival erosions over the tube among 25 eyes with a GDD. In 2 of these eyes, endophthalmitis developed, and among all 10 eyes, 6 devices were removed. The authors ascribed the erosions to rubbing by the edge of the soft lens. Chew and associates also reported 1 case of tube erosion from among 31 eyes. Moussally and Harissi-Dagher subsequently described 8 cases with a KPro plus a GDD, followed up for a mean of 24 months, without any tube erosion.

We would like to comment on our experience at the Massachusetts Eye and Ear Infirmary with tube erosion and endophthalmitis (presented as a poster at the American Glaucoma Society Meeting, March 4–7, 2011, Dana Point, California). We reviewed approximately 130 charts of patients with both a KPro and a GDD performed in the last 5 years. Nineteen erosions were found: 7 (37%) of 19 resolved without surgical intervention on change of contact lens. Five (26%) of 19 underwent tube revision. Four (21%) of 19 underwent tube explantation. Three (16%) of 19 have stable erosions to date with no leaks or hypotony. In none of these patients did endophthalmitis developed. Daily prophylactic drops with at least some efficacy against both gram-positive and gram-negative bacteria were used, for example, polymyxin B/trimethoprim or vancomycin (14 mg/mL) plus a fourth-generation fluoroquinolone. We agree with Li and associates that the mechanical trauma from the edge of the soft contact lens (usually a Kontur lens [Konkur Kontact Lens Co Inc, Hercules, California, USA] with a 16-mm diameter) is the main cause of tube erosions. In support of this theory, changing the diameter of the contact lens resolved the erosion in one third of our cases.

Moussally and Harissi-Dagher raised the question whether vancomycin toxicity to the conjunctiva could be a factor—Li and associates used a high concentration (50 mg/mL vs the more commonly chosen concentration of 14 mg/mL) twice daily for prophylaxis. However, this possibility still does not explain the resolution of the erosion with change in the contact lens diameter with continuation of vancomycin. We do not advocate the cessation of vancomycin use in high-risk patients because its use has for us dramatically reduced the rate of bacterial endophthalmitis from 12% in the decade 1990 through 1999 to 1% in the following decade, in similar patient populations (unpublished). Given that endophthalmitis did not develop in any of our patients with an exposed tube, we propose that tube erosions in patients with a KPro may not need to be managed very aggressively with surgical interventions unless clear hypotony or discomfort exists. Theoretically, with prophylactic antibiotics, an exposed tube through the conjunctiva should provide no more risk of endophthalmitis than the presence of a KPro, which is similarly exposed above the tissue surface. In addition, tube revision may not be an entirely harmless procedure—1 of the 2 endophthalmitis cases reported by Li and associates occurred after repair of the tube erosion.

Therefore, with the continued prophylactic use of a low-dose, broad-spectrum combination of antibiotics and changing the contact lens diameter, these patients may be given a chance to avoid further surgery with minimal risk of endophthalmitis and considerable likelihood of spontaneous recovery.