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Donald E. Mitchell, Kevin Duffy, Katelyn MacNeil; Enhanced Visual Recovery From Early Monocular Visual Deprivation in Kittens Promoted by Short Periods of Darkness. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3903.
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© ARVO (1962-2015); The Authors (2016-present)
Short periods of darkness reduce labeling for a cytoskeleton that supports neuron structure by forming a stable intracellular scaffold (Duffy et al , ARVO 2012). We reasoned that reduction of the cytoskeleton protein may increase plasticity so as to enhance the capacity for recovery for recovery from amblyopia. To this end we measured the consequences for the vision of the two eyes of periods of darkness (DR) imposed at different times following early monocular deprivation in kittens.
Nine kittens were monocularly deprived from either P30 for 7 days (N=7) or from P7 to P37 after which vision was binocular. Kittens were placed in darkness for 10 days either immediately after termination of the period of MD (N=4) or 5 to 8 weeks later. Binocular or monocular measurements of the visual acuity for gratings were made regularly by use of a jumping stand beginning from about the end of the period of MD. After the vision of the two eyes had stabilized, monocular and binocular measurements of depth perception and alignment accuracy were made on several animals (depth N=5; alignment N=2).
The 4 animals that were DR immediately following MD appeared temporarily blind in both eyes for 1-3 days after which the vision of the two eyes improved gradually in lock step without any relative impairment of the vision of the deprived eye. The two eyes achieved normal acuity in about 10 weeks. The severe amblyopia that developed in the 5 animals that remained in the light following MD disappeared rapidly in a week following 10 days of DR. At least one of these animals showed evidence of having developed stereopsis. Unlike animals placed in darkness immediately after MD, delayed imposition of DR did not affect vision in the non-deprived eye.
The 10-day period of DR had two previously unrecognized effects. First, when imposed early (at 5 weeks) but not later, (at 10 or 13 weeks), it had a temporary but detrimental effect on the vision of both eyes. This suggests a short critical period (< 70 days) during which cortical development may be temporarily disrupted through lack of visually-driven activity. Second, the period of DR prevented development of amblyopia when it occurred immediately after MD or else promoted rapid recovery from it when imposed later. Although the close similarity of the changes in cytoskeleton proteins and the behavioral effects of 10 days DR suggest a close link between the two, the latter may have other effects including changes in the cortical excitatory-inhibitory balance. As an initial step, complete elimination of light to both eyes for 10 days may facilitate current behavioral therapies for human amblyopia.
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