Interactions Between High-Intensity Light and Unrestricted Vision in the Drive for Hyperopia

Abstract

Purpose: To evaluate the impact of optical vs. illuminance factors and their duration-dependency on lens-induced hyperopia (LIH) in chick eyes.

Methods: Hyperopia was induced in one eye in chicks (10 groups; n = 126) from day 1 after hatching until day 8 using +10-diopter lenses with fellow eyes as controls. One group (LIH) served as the control without any interventions. The remaining groups were exposed to 2, 4, or 6 hours of unrestricted vision (UnV), high-intensity light (HL; 15,000 lux), or both (HL + UnV). Ocular axial length (AL), refractive error, and choroidal thickness were measured on days 1, 4, and 8. Inter-ocular difference (IOD = experimental - contralateral control eye) ± SEM was used to express outcome measures.

Results: By day 8, LIH decreased AL (-0.42 ± 0.03 mm) and produced hyperopic refraction (+3.48 ± 0.32 diopters) and choroidal thickening (+85.81 ± 35.23 µm) in the LIH group (all P < 0.001). Exposure to UnV reduced LIH (i.e., hyperopic refraction, axial shortening, and choroidal thickening) in a duration-dependent manner, whereas HL potentiated the development of LIH in a duration-dependent manner. When combined, UnV overpowered HL, with resultant impact on refraction and AL being close to UnV alone, except at 6 hours, when HL + UnV induced shorter AL compared with UnV alone (P = 0.03).

Conclusions: Daily exposure to HL, UnV, and HL + UnV altered LIH in a duration-dependent manner with UnV and LIH producing competing signals. The signal generated by UnV was generally stronger than HL in combined exposure, yet longer durations of HL affected the drive for emmetropization in eyes with UnV.

Figure 1.

IOD in refraction, AL, and CT on days 1, 4, and 8 of the experimental protocol in the group not exposed to any intervention (LIH) and groups exposed to 2 hours of HL, UnV, or both (HL + UnV).

Figure 2.

IOD in refraction, AL, and CT on days 1, 4, and 8 of the experimental protocol in the group not exposed to any intervention (LIH) and groups exposed to 4 hours of HL, UnV, or both (HL + UnV). For significant group effect: *P < 0.05, **P < 0.01, ***P < 0.001 (two-way repeated-measures ANOVA).

Figure 3.

IOD in refraction, AL, and CT on days 1, 4, and 8 of the experimental protocol in the group not exposed to any intervention (LIH) and groups exposed to 6 hours of HL, UnV, or both (HL + UnV). All groups are significantly different from the LIH + HL group: ^†††P < 0.001. For significant group effect: *P < 0.05, **P < 0.01, ***P < 0.001 (two-way repeated-measures ANOVA).

Figure 4.

Duration–response curve for the IOD in refraction (A), AL (B), and CT (C) in the groups exposed to 2, 4, and 6 hours of HL, UnV, or both (HL + UnV) on day 8 of the experimental protocol. The LIH group that was not exposed to any intervention is represented by a white square and a shaded area for mean ± 95% confidence interval. HL is significantly different from the other two groups: ^‡‡P < 0.01, ^‡‡‡P < 0.001. All the groups are different from each other: ^†P < 0.05 (at least). The HL group is significantly different from both UnV and HL + UnV groups: *P < 0.05, **P < 0.01, ***P < 0.001.