Table 1.
Classification of DRS
| Classification system | Basis of classification | |
|---|---|---|
| Papst41–43 | Abnormal co-contraction | 1. MR and LR |
| 2. Superior rectus and LR | ||
| 3. Inferior rectus and LR | ||
| 4. LR and other muscles | ||
| Malbran44 | Motility | Type I: Palsy of abduction |
| Type II: Palsy of adduction | ||
| Type III: Limitation of depression and elevation without impairment of horizontal movements | ||
| Lyle and Bridgeman45 | Motility | Type A: Abduction more deficient than adduction, but both are deficient. Adduction causes globe retraction and palpebral fissure narrowing |
| Type B: Abduction is deficient, but not adduction | ||
| Type C: Abduction less deficient than adduction, but both are deficient. Adduction causes globe retraction and palpebral fissure narrowing | ||
| Huber46 | EMG | Type I (70%–80%): Marked limitation of abduction with minimally defective or normal adduction, globe retraction and palpebral fissure narrowing in adduction, widening in abduction |
| EMG recordings showed paradoxical innervations of the LR with maximum impulses on adduction and defective impulses in attempted abduction. MR was found to have normal electric behavior | ||
| Type II (7%): Marked limitation of adduction with primary position exotropia of the affected eye, abduction normal or slightly limited with globe retraction and palpebral fissure narrowing in attempted adduction | ||
| On EMG, LR showed peak impulses on abduction and a second paradoxical impulse on attempted adduction, while the electrical activity of MR was normal | ||
| Type III (15%): Limitation or complete absence of adduction and abduction with globe retraction and palpebral fissure narrowing in attempted adduction | ||
| EMG showed simultaneous innervation of LR and MR muscles in primary gaze, adduction and abduction | ||
| Huber also went on to describe the alphabet patterns of strabismus, which are also seen in DRS, suggesting that there are groups of patients wherein the vertical rectus has this synergistic innervation |
Abbreviations: DRS, Duane retraction syndrome; EMG, electromyography; LR, lateral rectus; MR, medial rectus.