Dynamic interactions of eye and head movements when reading with single-vision and progressive lenses in a simulated...

To assess dynamic interactions of eye and head movements during return-sweep saccades (RSS) when reading with single-vision (SVL) versus progressive-addition (PAL) lenses in a simulated computer-based business environment.

Horizontal eye and head movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of single-page (SP; 14 degrees horizontal [H]) and double-page (DP; 37 degrees H) formats at 60 cm with binocular viewing. Subjects included 11 individuals with normal presbyopic vision aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses with a different clear near field of view (FOV): a SVL (60 degrees H clear FOV), a PAL-I with a relatively wide intermediate zone (7.85 mm; 18 degrees H clear FOV), and a PAL-II with a relatively narrow intermediate zone (5.60 mm; 13 degrees H clear FOV).

Eye movements were initiated before head movements in the SP condition, and the reverse was found in the DP condition, with all three lens types. Duration of eye movements increased as the zone of clear vision decreased in the SP condition, and they were longer with the PALs than with the SVL in the DP condition. Gaze stabilization occurred later with the PALs than with the SVL in both the SP and DP conditions. The duration of head movements was longer with the PAL-II than with the SVL in both the SP and DP conditions. Eye movement peak velocity was greater with the SVL than the PALs in the DP condition.

Eye movement and head movement strategies and timing were contingent on viewing conditions. The longer eye movement duration and gaze-stabilization times suggested that additional eye movements were needed to locate the clear-vision zone and commence reading after the RSS. Head movements with PALs for the SP condition were similarly optically induced. These eye movement and head movement results may contribute to the reduced reading rate and related symptoms reported by some PAL wearers. The dynamic interactions of eye movements and head movements during reading with the PALs appear to be a sensitive indicator of the effect of lens optical design parameters on overall reading performance, because the movements can discriminate between SVL and PAL designs and at times even between PALs.