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A.K. McAuley, M.J. Murphy, J. Davidson, S. Scott, M.J. Goodyear, A. Guadagnuolo, S.G. Crewther; Refractive Compensation in Chicks Raised Under Low Temporal Frequency Flicker with Pharmacological Inhibition of the Retinal ON Pathway . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1143.
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Controversy exists as to the site of control of refractive compensation to optical defocus. Low temporal frequency light manipulation, presumably initiating action in the outer retina, promotes a myopic shift in refractive compensation to all lens wear. L α amino adipic acid (LAAA) selectively inhibits retinal ON pathways and suppresses refractive compensation to negative lenes via action on the photoreceptor bipolar synapse. Thus, the current study investigated the interaction between the effect on refractive compensation and ocular growth of low frequency whole field temporal flicker and the inhibition of the ON pathway.
209 chicks were fitted with monocular +10D, –10D and No lenses raised from day 5–9 post–hatchling in a 12 hour light/day temperature controlled box under normal light conditions or 1 Hz Temporal Luminance Modulation (TLM) with exposure duration of 250msec. TLM ranged between 1.8–183lux. Right eyes were injected with 5µl of 2.5 µmol LAAA or PBS and left eyes with 5µl PBS. Refractive state and ocular dimensions were measured and ANOVA was conducted on the difference between eyes. Eyes were prepared for histological and immunological analysis.
As expected 1Hz TLM induced a myopic shift in refraction and axial dimensions for all lens, and LAAA inhibited compensation to –10D but not +10D lens–wear though there was a decrease in anterior chamber depth. The effect of TLM and LAAA closely reflected refractive compensation under TLM alone. Alterations in refractive state were closely reflected in growth in axial length, mostly occurring in the vitreous chamber though lens–wear under saline or no drug conditions with TLM resulted in a general increase in anterior chamber depth irrespective of lens.
The combination of the two manipulations demonstrated no difference from TLM alone indicating that TLM has a more powerful effect on eye growth and refraction than LAAA. This suggests that the signal for growth originates earlier than the photoreceptor/bipolar synapse or that the ON system is not important in TLM produced myopic shifts.
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