Purpose:
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.
Methods:
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.
Results:
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.
Keywords: myopia • choroid • refractive error development