| Class I | Any ocular muscle weakness May have weakness of eye closure All other muscle strength is normal |
| Class II | Mild weakness affecting other than ocular muscles May also have ocular muscle weakness of any severity |
| IIa | Predominantly affecting limb, axial muscles, or both May also have lesser involvement of oropharyngeal muscles |
| IIb | Predominantly affecting oropharyngeal, respiratory muscles, or both May also have lesser or equal involvement of limb, axial muscles, or both |
| Class III | Moderate weakness affecting other than ocular muscles May also have ocular muscle weakness of any severity |
| IIIa | Predominantly affecting limb, axial muscles, or both May also have lesser involvement of oropharyngeal muscles |
| IIIb | Predominantly affecting oropharyngeal, respiratory muscles, or both May also have lesser or equal involvement of limb, axial muscles, or both |
| Class IV | Severe weakness affecting other than ocular muscles May also have ocular muscle weakness of any severity |
| IVa | Predominantly affecting limb and/or axial muscles May also have lesser involvement of oropharyngeal muscles |
| IVb | Predominantly affecting oropharyngeal, respiratory muscles, or both May also have lesser or equal involvement of limb, axial muscles, or both |
| Class V | Defined by intubation, with or without mechanical ventilation, except when employed during routine postoperative management. The use of a feeding tube without intubation places the patient in class IVb. |
