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Man Pan Chin, Zhe Chuang Li, Allen Ming Yan Cheong, Ho Lung Henry Chan, Laboratory of Experimental Optometry (Neuroscience); Compensatory eye growth responded to the imposed defocus is influenced by spatial content in chick. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2168. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Emmetopization is a visually guided eye growth, and the compensatory eye growth is depending on the imposed defocus. This study hypothesized if different spatial contents can affect the compensatory eye growth responded to imposed defocus.
The right eyes of White Leghorn chicks from 10 to 12 days old were glued with a cone-shaped lens system using Velco. Animals were divided into six groups (n=8 to 12) for various levels of defocus magnitude, including plano, -15D and -25D (lenses were attached at the proximal end of the cone), with two different spatial stimulus patterns at the other end of the cone: 1) high spatial frequency: 0.88 cycle/deg (0.4mm white/black checkers) with 100% of contrast, and 2) a lower spatial frequency: 0.28 cycle/deg (1.25mm white/black checkers) with 100% of contrast. Axial ocular dimensions, including anterior chamber depth, lens thickness, vitreous chamber depth (VCD) and axial length, were obtained using A-scan ultrasound. Measurement was carried out prior to fitting the lens system and on the fourth day after treatment. Analysis of variance (ANOVA) was used for statistical analysis.
After 4 days of wearing the cones, the VCD of the right eye increased with the imposed defocuses. Under the same magnitude of defocus, chick eyes with low spatial stimulus had consistently longer VCD than those with high spatial stimulus (p<0.05). Both defocus and spatial stimulus showed significant main effect on VCD percentage change (ANOVA, p<0.005). Significant group differences of VCD percentage change were observed in Group -15D (low vs high, 10.4±2.2 vs 7.25±3.35, p<0.05) and -25D (9.53±3.82 vs 4.93±4.79, p<0.05), but not in plano group. Similar trend was also observed in axial length, but neither in anterior chamber depth nor lens thickness.
Our results confirm our hypothesis that spatial content in emmetropization can affect the compensatory eye growth responded to same magnitude of imposed defocus. Effects of different optical defocus on compensatory eye growth significantly interacted with the spatial frequency of the visual stimulus. Further studies are important to understand the mechanism of defocus and spatial interaction in emmetropization.
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