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H. Guan, C. Wildsoet; Myopia Induced by Intravitreal Quisqualic Acid in Young Chicks Has a Corneal Origin and Is not Altered by Imposed Defocus. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5926.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies using intravitreal quisqualic acid (QA) to probe the retinal circuitry underlying eye growth regulation and emmetropization in chicks report a loss of the defocus sign discrimination but not blur detection (Bitzer & Schaeffel, 2004). Because we see a similar effect of optic nerve section, using multifocal "simultaneous vision" (MF) lenses (Wildsoet & Collins, 2000), we looked for a direct parallel between these 2 studies by combining the latter lenses with QA.
White Leghorn chicks had one eye fitted with plano, +10D, or +10/-10D MF lenses (n=6 per group), 6 days after injection with either 200 nm QA or vehicle (saline) at hatching; fellow eyes were injected with vehicle. Lenses were worn for 5 days. Some chicks were left without lenses (n=3). Refraction and eye growth were monitored using retinoscopy and high frequency A-scan ultrasound; measurements were made prior to injection, immediately prior to lens fitting, and at various times during the pre- and post-lens periods.
The QA injection induced a sustained choroidal thickening (CT), reflected in a ~2-fold difference in CT between otherwise treated and fellow eyes by day 6, and coupled to high hyperopia (+6.8 ±1.7D). A delayed increase in corneal dimensions (anterior chamber depth: 2.5 ±0.06 vs. 1.5 ±0.04 mm; cornea diameter: 7 ±0.02 vs. 6.2 ± 0.04mm, observed over the last 5 days of monitoring, resulted in a myopic refractive shift (+1.1 ±2.9D). The 3 QA-lens-treated groups showed similar growth changes, although there was a transient slowing of the increase in CT over the first day of lens wear. In contrast, choroidal thickening was confined to the +10 and +10/-10D MF lens-vehicle groups and resulted in increased hyperopia. There was little difference between the plano lens-treated eyes and their fellows for the vehicle group.ConclusionThe similarity of the response profiles of QA-treated eyes, irrespective of their defocus experience, implies a compete disruption of the emmetropization process. Nonetheless, this QA model has the potential to provide new insights into the signal pathways regulating both the choroidal thickening response and corneal development.
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