Impact of zone geometry on the introduction of myopic defocus in young adult eyes wearing multi-zone lenses.

PURPOSE

Multizone contact lenses control myopia progression by proposed introduction of myopic defocus. This project investigated how much of the pupil area and how many dioptres of myopic defocus are introduced by different lens zone geometries with near- and off-axis viewing.

METHODS

Ten young myopic adults (18-25 years) binocularly wore four soft contact lenses including a single vision (SV), concentric-ring dual-focus (DF), centre-distance multifocal (MF) and a RingBoost™ (RB) multi-zone design containing a combination of coaxial and non-coaxial zones. A modified aberrometer captured aberrations and pupil sizes at four target vergences between -0.25 and -4.00 D (on-axis) and across the central ±30° of the horizontal retina (off-axis). Defocus was quantified as the difference between the measured refractive state and the target vergence within each zone of a multi-zone design within the pupil and compared with that of equivalent zone areas of the SV lens. The percentage of the pupil containing myopic defocused light for each lens was calculated.

RESULTS

Defocus within the distance correction zones of multi-zone lenses was similar to that of the SV lens. When viewing on-axis at -0.25 D target vergence, on average 11% of the pupil was myopic with SV, whereas 62%, 84% and 50% of the pupil was myopic for the DF, MF and RB designs, respectively. At -4.00 D target vergence, all lenses exhibited a systematic decrease in the percentage of pupil area having myopic defocus (SV: 3%; DF: 18%; MF: 5% and RB: 26%). The off-axis proportions were similar across multi-zone lenses; however, multi-zone lenses retained approximately 1.25-3.0× more myopic defocus than the SV lens.

CONCLUSIONS

Subjects accommodated using the distance-correction zones of multi-zone lenses. Multi-zone contact lenses introduced significant myopic defocus on-axis and across the central ±30° retina. However, the magnitude and proportion of defocus were influenced by zone geometry, add power and pupil size.