Abstract
Purpose::
To study of the properties of ONHC produced by the protocol in VERIS Version 5, and to observe changes in the ONHC in an experimental glaucoma in a monkey model.
Methods::
Recordings were made from normal anesthetized monkeys and monkeys with monocular experimental glaucoma. The mfERG stimulus had five frames in each m-step: the 1st with focal flashes (200cd/m sq) determined by the m-sequence, the 2nd and 4th frames contained a global flash (200 cd/m sq), and the 3rd and 5th frames were dark (2 cd/m sq). An algorithm based on Sutter & Bearse (1999) was used to obtain the retinal component (RC) and the ONHC from recordings in normal eyes. Implicit time and amplitude of the ONHC were measured. The glaucoma-sensitive component was derived by subtracting recordings from glaucomatous eyes from those from normal fellow eyes. Fourier Transform was used for power spectrum analysis. Perimetry and optical coherence tomography (OCT) tests were also done on glaucomatous monkeys.
Results::
The algorithm could reliably decompose signals from normal eyes into RC and ONHC. There were five major wave components between 20 and 80 ms in the ONHC. Power spectral analysis of RC and ONHC templates revealed that although the power distribution of the two components overlapped in frequency domain, the ONHC received a more prominent contribution from frequencies < 75Hz, while the RC had relatively more power in the range > 75 Hz. In eyes with severe glaucoma (MD worse than -10 dB), the ONHC could not be extracted, but the glaucoma-sensitive components had similar timing and power distributions to those of the ONHC, and retinal nerve fiber layer thickness (RNFLT) was reduced in all regions. In eyes with moderate sensitivity loss (i.e. MD between - 5 to -10 dB), regional RNFLT reduction and ONHC changes were observed.
Conclusions::
The ONHC protocol could generate an easily identifiable ONHC in normal monkey eyes, which was rich in low frequency components. The ONHC was a major contributor to glaucoma-sensitive component.
Keywords: electroretinography: non-clinical • ganglion cells • optic nerve