Abstract
This study assessed axial length and choroidal thickness changes following short-term peripheral myopic defocus in normal adult subjects. Twenty subjects underwent defocus sessions by viewing a full-field projected movie 4 m away for 4 h in the morning, while wearing spectacle lenses, corrected for distance vision in both eyes. The right eye, serving as the test eye, was peripherally defocused using a Fresnel lens overlay of + 3.50 D with a central clear aperture of 11.5 mm (correlating to a clear central visual field of approximately 23°), while the left eye served as the control (with no Fresnel lens overlay). A subset of 10 subjects from the same cohort also underwent additional defocus sessions with + 5.00 D of peripheral defocus. Axial length was measured and radial sub-foveal choroidal scans were obtained before and after the defocus sessions. The increase in axial length of the test eyes were significantly less than the control eyes under both peripheral defocus conditions (p < 0.05). The difference in mean change for choroidal thickness between test and control eyes was not significant for either dioptric condition. Our results demonstrated that short-term peripheral myopic defocus significantly inhibited axial elongation in adult humans, without significant changes in choroidal thickness.
Highlights
The human eye is sensitive to the presence of light as well as its optical vergence direction
The mean axial length elongation was significantly less for the test eye as compared to the control eye after 4 h of peripheral myopic defocus for both defocus conditions (t = 2.47, df = 38, corrected p = 0.036 for + 3.50 D defocus condition; and t = 2.73, df = 18, corrected p = 0.027 for + 5.00 D defocus condition after Bonferroni’s correction for multiple comparisons)
For the + 5.00 D peripheral defocus condition, the sub-foveal choroidal thickness in the control eye thinned by 4 μm, while the test eye thickened by 7 μm compared to the baseline
Summary
The human eye is sensitive to the presence of light as well as its optical vergence direction. Several human studies have shown that the eye can sense the direction of full-field defocus relative to the retinal surface, whether myopic, hyperopic, or astigmatic in n ature[1,2,3,4,5] This physiological phenomenon has been investigated by measuring the central axial length (from the anterior part of the cornea to the posterior retinal pigment epithelium) and the central (sub-foveal) choroidal thickness, before and after controlled defocus sessions. Smith et al (2007) showed that peripheral defocus cues only (without central defocus cues) were able to affect axial elongation in rhesus monkeys They accomplished this by ablating the central 10°–12° of the visual field and using various plus and minus lenses as defocus stimuli. Further research is needed to investigate underlying factors (e.g., duration, magnitude, direction, and location of defocus) that contribute to such physiological changes across different species, especially humans
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