Comparison of primary position measurements and abduction deficit between type 1 Duane syndrome and sixth cranial nerve palsy.

BACKGROUND

Unilateral Duane retraction syndrome type 1 (DRS-I) and unilateral sixth nerve palsy (6NP) present with limitation of abduction, incomitant esotropia, and frequently, a compensatory head turn. The purpose of this study was to compare the mean primary position measurement and to correlate this with the abduction deficit to determine if these measurements may be used to differentiate between the 2 conditions when other clinical signs of DRS-I (globe retraction, changes in lid fissure height, and upshoots/downshoots) are subtle.

METHODS

A database search of patients examined over a 5-year period revealed 69 cases of DRS-I and 62 cases of unilateral 6NP. Primary position measurements both at distance and near and limitation of abduction on version testing were recorded and compared.

RESULTS

Mean abduction deficit was -3.5 ± 0.1 for DRS-I and -2.6 ± 0.2 for 6NP (P = 0.0004). Mean esotropia at near was 8.4 ± 1.1 prism diopters (PD) for DRS-I and 27.2 ± 2.4 PD for 6NP (P < 0.0001). Mean esotropia at distance was 10.3 ± 1.3 PD for DRS-I and 36.4 ± 2.4 PD for 6NP (P < 0.0001). The mean distance-near disparity for DRS-I was 1.94 ± 0.62 PD and 9.19 ± 1.28 PD for 6NP (P < 0.0001). The age-group of ≤2 years consisted of 23 DRS-I and only 2 6NP cases. The age-group between >2 years and <18 years had 41 DRS-I and 16 6NP cases, respectively. Finally, the age-group of ≥18 years had only 5 DRS-I and 44 6NP cases (P < 0.0001).

CONCLUSION

Patients with DRS-I showed greater abduction deficit yet significantly less esotropia in primary position than those with 6NP. Patients with 6NP were more likely to have a significant distance-near disparity. In addition, patients with DRS-I tended to be younger than those with 6NP. This report documents that DRS-I and 6NP can be differentiated based on magnitude of primary position esotropia, comparison of primary position esotropia with severity of abduction deficit, distance-near disparity, and patient age.