Vertical strabismus in monofixation syndrome.

Purpose: The manifest angle of the horizontal deviation in monofixation syndrome (MFS) has been reported to reach a maximum of 8 to 10 PD. Review of the literature, however, revealed no studies about the vertical deviation associated with MFS. The purpose of this study is to evaluate the range of the angle of the vertical deviation in MFS.

Methods: Forty patients who had MFS with vertical strabismus in the distance primary position were included in this study. All fulfilled the criteria for monofixation, fusing Worth 4 dots at near but suppressing at distance and/or having stereoacuity between 3000 and 60 seconds of arc by using Titmus stereotest and a horizontal deviation within 8 PD of orthophoria by simultaneous prism and cover test. Patients were divided into 3 groups: patients with hypertropia without any dissociated vertical deviation (DVD) (group I), patients with only DVD (group II), and patients with both hypertropia and DVD (group III).

Results: Eighteen patients (45.0%) had hypertropia only (group I), 15 (37.5%) had DVD only (group II), and 7 (17.5%) had both (group III). In groups I and III the angle of hypertropia by simultaneous prism and cover test was 2 to 6 PD (mean, 3.9 PD) and in group II and III the angle of DVD was 4 to 14 PD (mean, 7.5 PD) at distance.

Conclusions: These results suggest that in MFS the angle of hypertropia can range up to a maximum of 6 PD. However, monofixation was observed in patients with a larger absolute angle of DVD (up to 14 PD), possibly due to an intermittent nature of the DVD.