Force development and velocity of saccadic eye movements in exotropia

Abstract

The authors have measured saccadic peak velocity with elec-trooculography (EOG) and force development with a suction contact lens/strain gauge technique in 11 patients with intermittent exotropia (IXT) and ten patients with constant exotropia (CXT). Saccadic movements with the dominant eye fixating were elicited horizontally to targets positioned at 5, 10 and 20 deg in the adduction and abduction fields of gaze, and vertically to targets at 10 deg in the 20 deg adduction and abduction fields of gaze. Peak velocity (Vp) was measured in both eyes and peak force (Fp) and steady-state force (Fs) in the deviated eye. Fp of abduction was higher in CXT patients than in normals, while Fp in adduction was higher in IXT than in normals and CXT. Vp did not show clear differences between patients and normals. However, the ratios of Vp(abd/add) and Fp(abd/add) of the deviated eye were significantly higher in CXT and lower in IXT than in normals. This is probably related to fusion induced muscle activity in IXT and the lack of such activity in CXT. Imbalances of vertical Fp and Vp were found in the adduction field of gaze in the patients with A- or V-patterns and oblique muscle dysfunction.

Key Words:

• Intermittent and constant exotropia
• saccadic peak velocity
• isometric force