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In Myopia, an ocular or “front-end” condition that
typically develops after the critical period, there is often a mismatch
between the changed optic and the neural connections formed during early
childhood. The neuronal connectivity is developed normally and is capable of
processing images efficiently; however the visual input is subnormal and
limited by optics. The visibility of high spatial frequencies is perceived
as low contrast even when their physical contrast is high. Thus, CSF is
reduced at the high spatial frequencies, resembling the amblyopic CSF,
which, as a consequence, degrades visual acuity (VA). In particular, reduced
signal strength is expected to degrade letter identification, as
demonstrated by a recent study23. In this study the level of noise was
systematically increased, followed by a parallel degradation in letter
recognition. Activation of neurons in the visual cortex is directly related
to signal strength (contrast)-- when the effective contrast is low, neurons
are weakly activated. Thus, the S/N ratio is low, which consequently limits
performance on letter identification (VA) as indicated in the previously
mentioned study.
Clinical Results
NVC trains neural
interactions by efficiently stimulating the specific neurons and effectively
promoting spatial interactions among these neurons. All amblyopic subjects
had their CSF measured before training to determine the starting
spatial-frequency. The amblyopic CSF showed higher thresholds (lower
sensitivities) as compared with normal vision subjects, with the low
spatial-frequencies close to normal and the high spatial-frequencies showing
the strongest sensitivity loss. NVC produced a
significant improvement of sensitivity in the high spatial-frequency range,
raising it to within the normal range. Furthermore, inhibition was greatly
reduced after treatment, indicating a change in the neuronal interactions
occurring within the primary visual system. The improvement in neuronal
interactions and CSF was accompanied by a remarkable improvement in VA in
the amblyopic patients (80% average improvement).
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