Multifocal ERG wavelet packet decomposition applied to glaucoma diagnosis

Abstract

BackgroundGlaucoma is the second-leading cause of blindness worldwide and early diagnosis is essential to its treatment. Current clinical methods based on multifocal electroretinography (mfERG) essentially involve measurement of amplitudes and latencies and assume standard signal morphology. This paper presents a new method based on wavelet packet analysis of global-flash multifocal electroretinogram signals.MethodsThis study comprised twenty-five patients diagnosed with OAG and twenty-five control subjects. Their mfERG recordings data were used to develop the algorithm method based on wavelet packet analysis. By reconstructing the third wavelet packet contained in the fourth decomposition level (ADAA4) of the mfERG recording, it is possible to obtain a signal from which to extract a marker in the 60-80 ms time interval.ResultsThe marker found comprises oscillatory potentials with a negative-slope basal line in the case of glaucomatous recordings and a positive-slope basal line in the case of normal signals. Application of the optimal threshold calculated in the validation cases showed that the technique proposed achieved a sensitivity of 0.81 and validation specificity of 0.73.ConclusionsThis new method based on mfERG analysis may be reliable enough to detect functional deficits that are not apparent using current automated perimetry tests. As new stimulation and analysis protocols develop, mfERG has the potential to become a useful tool in early detection of glaucoma-related functional deficits.

Wavelet decomposition analysis in the two-flash multifocal ERG in early glaucoma: a comparison to ganglion cell analysis and visual field

“…Some of the differences between our findings and those of Miguel-Jiménez et al [ 27 – 29 ] may be related not only to the different glaucoma stages analyzed, but also to the different selection of areas analyzed: only areas with field defect versus the central 15°, irrespective of the location of the field defect. Differences may also result from the use of different visual field patterns.…”

“…In a subsequent paper, using discrete wavelet packet decomposition analysis the same group focused on the induced component (60–90 ms) of their global flash mfERG. Analysis of the visual field sectors affected by glaucoma in 25 OAG patients found a sensitivity of 0.81 and a specificity of 0.73 [ 29 ]. Further, using CWT (Morlet waveform) in OAG and healthy subjects, sensitivity could be increased to 0.894 and specificity to 0.844, again only including sectors identified as glaucomatous and again looking at the induced component [ 27 ].…”

“…For glaucoma, Miguel-Jiménez et al have successfully applied DWT to the global flash mfERG response in advanced glaucoma. They analyzed a number of mother templates (not specified) and on visual comparison found the mother template Bior 3.1 to have the best performance [ 29 ]. In a later paper, they applied continuous wavelet transform using the Morlet waveform [ 27 ] with good results.…”

“…Lately, he applied DWT to assess the contribution of the oscillatory potentials to the full-field ERG [ 26 ]. With specific focus in glaucoma Miguel-Jiménez et al [ 27 ] applied different types of wavelet analysis to the global flash mfERG response in glaucoma and found that CWT analysis, discrete wavelet transform (DWT) [ 28 ] and discrete wavelet packet transform [ 29 ] can separate advanced glaucoma from control and give additional information to the defect seen on Humphrey visual fields from these patients.…”

Objective perimetry using a four-channel multifocal VEP system: correlation with conventional perimetry and thickness of the retinal nerve fibre layer

“…The recording with the highest SNR was automatically chosen to represent the response to the relevant visual field. Future studies with more sophisticated filter methods27 28 might be able to optimise the ratio between the evoked signal and the base level. A drawback of the mfVEP technique as an objective perimetry method is the relatively long recording time necessary for reliable data and the possible influence of movements or muscle tension.…”