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T.N. Hwang, W.–T. Park, T. Kenny, T. McCulley; A Novel Mechanism for Indirect Traumatic Optic Neuropathy . Invest. Ophthalmol. Vis. Sci. 2006;47(13):741.
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© ARVO (1962-2015); The Authors (2016-present)
The study investigates a possible mechanism of indirect traumatic optic neuropathy by asking whether the soft tissue wave generated by blunt force trauma to the front of a skull is focused within orbit as it moves toward the orbital apex. This is the same mechanism by which a simple cone can collect and amplify sound waves. When a wave travels through a cone from the larger opening towards the smaller opening, the wave reflects off the walls of the cone as the diameter gets progressively smaller, generating additional waveform components and turbulence.
A human cadaver head was struck with a rubber mallet to simulate blunt trauma. Accelerometers (Analog Devices, Inc. Model ADXL210E – low–cost 10g Dual–Axis), placed in the orbit and on the superior scalp, recorded movement during a series of impacts directed both to the forehead and to the back of the skull. Average waveforms for the accleration measured at the different locations were generated and compared. To detect the presence of any reflected wave components created by the impact, Fourier transformation methods were used to compare the freqeuency profile of the acceleration waveforms measured under the different conditions.
The acceleration waveform within the orbit during the front impact had additional oscillations that were not observed during rear impacts or during measurements on the scalp. Fourier analysis showed that the freqeuency spectrum of the acceleration waveform measured within the orbit had more power in the higher frequency components greater than 400 Hz during anterior blunt trauma compared to the acceleration measured in the orbit during posterior blunt trauma or on the scalp during either anterior or posterior blunt trauma.
Frontal impact to the skull results in higher frequency oscillations within the orbit which are not seen with similar posterior impacts. This is consistent with a reverberation effect within the orbit generated by the orbit acting as a collecting cone to funnel the soft tissue wave created by the impact. This higher frequency turbulence and energy may play a casusative role in indirect traumatic optic neuropathy.
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