| Index of Global Cortical Function (IGCF) | VEPs | SEPs |
| Grade 0 | Normal | Normal |
| Grade 1 | Delayed peak III Peak VII present | Normal N20, P24, P27 N30 present |
| Grade 2 | Delayed peak III Peak VII present | Normal N20, P24 N30 basent |
| Grade 3 | Delayed peak III | Normal N20 |
| Grade 4 | No reproducible VEPs ERG present | P14 present |