Effect of a longpass filter on myopic defocus-induced changes in axial length and choroid thickness

To investigate the short-term effect of a longpass filter on myopic defocus-induced changes in axial length (AL) and choroidal thickness (ChT).

This study included 23 young myopic adults. AL and ChT were measured in both eyes before and after 60 min of +5 D myopic defocus induced in the right eye with either a longpass filter (>495 nm) or a neutral density (ND) filter of equal transmittance. The same ND filter was used for both the left eye and the control eye. The pupil diameter of the left eye was measured before and 10 min after each test session. Illumination was maintained at 100 lux.

After 60 min of monocular defocusing with the ND filter, a significant reduction in AL (mean±SE) was observed in the right eye (-8.20 ± 3.01 μm; t = -2.72; p = 0.01). However, no significant change was noted in ChT (-0.73 ± 1.78 μm; t = -0.41; p = 0.69). With the longpass filter, no significant change in AL was observed (-1.11 ± 4.27 μm, t = -0.26, p = 0.80), but a significant reduction in ChT was observed (-4.56 ± 1.73 μm, t = -2.63, p = 0.02). Pupil size did not significantly differ between the two filters (F = 0.004, p = 0.95).

Blocking short wavelengths inhibited the acute axial shortening response to myopic defocus, suggesting a modulatory role of short wavelengths in refractive development under the present experimental conditions.