The cumulative risk factor index (CRFI): preoperative characterisics known to have an adverse effect on the surgical outcome of filtration surgery were each ascribed a score and the total calculated
| Preoperative characteristic | Score |
|---|---|
| Black race | 1 |
| Previous incisional ocular surgery | 1 |
| ⩾ 2 topical medications for ⩾ 18 months | 1 |
| 30 years ⩽ age ⩽ 50 years | 1 |
| Age ⩽ 30 years | 2 |
| Complicated glaucoma | 1 |
↵Complicated glaucoma = any glaucoma other than primary open and capsulare types.
Risk factor (RF) group A = 1–2 points, RF group B = 3–4 points, RF group C = 5–6 points.