Risk factor for bleb failure
| Risk factor for failure | Number |
| Previous failed trabeculectomy | 7 |
| Previous failed trabeculectomy and Afro-Caribbean race | 2 |
| Previous failed trabeculectomy and cataract extraction | 4 |
| Previous cataract extraction | 2 |
| Previous cataract extraction and Afro-Caribbean race | 1 |
| Uveitis | 3 |
| Uveitis and age less than 50 | 1 |
| Age less than 50 | 1 |