A fast automated method for calculating the EOG Arden ratio.

BACKGROUND: Recording of the dark trough/light peak of the electrooculogram (EOG) remains a useful electrodiagnostic tool. Manual analysis of the recording is tedious and lengthy, and automated analysis needs to deal with artefacts due to suboptimal patient cooperation. METHODS: We present a novel method of automating the processing and analysis of raw EOG data using the open-source statistical software R. Rather than attempting saccade detection, we utilize the fact that basic properties of the response (rough waveform timing) are known and simply fit a square wave to each response run-free parameters are amplitude and phase. To assess this analysis method, responses from 54 eyes of 27 patients with a variety of ophthalmic diagnoses were analysed with manual calculation and with a number of automated methods of fitting the response curve. The Arden ratio was the main outcome measure. RESULTS: Robust regression of a fundamental with a three-harmonic approximation of a square wave was found to be the best method. Classification accuracy with this method compared with the manual calculations as gold standard; using a lower normal threshold of 200%, Arden ratio was found to achieve a sensitivity of 96% and specificity of 81%. Time taken to process and analyse the data for a subject was reduced from 20 min for the manual method to 2 min for the automated method. CONCLUSIONS: The simple approach yielded a surprisingly effective automatic estimation of the Arden ratio. In one author's laboratory (MB), this procedure has proved to be useful over 5 years for routine analysis.

More than blindsight: Case report of a child with extraordinary visual capacity following perinatal bilateral occipital lobe injury.

Injury to the primary visual cortex (V1, striate cortex) and the geniculostriate pathway in adults results in cortical blindness, abolishing conscious visual perception. Early studies by Larry Weiskrantz and colleagues demonstrated that some patients with an occipital-lobe injury exhibited a degree of unconscious vision and visually-guided behaviour within the blind field. A more recent focus has been the observed phenomenon whereby early-life injury to V1 often results in the preservation of visual perception in both monkeys and humans. These findings initiated a concerted effort on multiple fronts, including nonhuman primate studies, to uncover the neural substrate/s of the spared conscious vision. In both adult and early-life cases of V1 injury, evidence suggests the involvement of the Middle Temporal area (MT) of the extrastriate visual cortex, which is an integral component area of the dorsal stream and is also associated with visually-guided behaviors. Because of the limited number of early-life V1 injury cases for humans, the outstanding question in the field is what secondary visual pathways are responsible for this extraordinary capacity? Here we report for the first time a case of a child (B.I.) who suffered a bilateral occipital-lobe injury in the first two weeks postnatally due to medium-chain acyl-Co-A dehydrogenase deficiency. At 6 years of age, B.I. underwent a battery of neurophysiological tests, as well as structural and diffusion MRI and ophthalmic examination at 7 years. Despite the extensive bilateral occipital cortical damage, B.I. has extensive conscious visual abilities, is not blind, and can use vision to navigate his environment. Furthermore, unlike blindsight patients, he can readily and consciously identify happy and neutral faces and colors, tasks associated with ventral stream processing. These findings suggest significant re-routing of visual information. To identify the putative visual pathway/s responsible for this ability, MRI tractography of secondary visual pathways connecting MT with the lateral geniculate nucleus (LGN) and the inferior pulvinar (PI) were analysed. Results revealed an increased PI-MT pathway in the left hemisphere, suggesting that this pulvinar relay could be the neural pathway affording the preserved visual capacity following an early-life lesion of V1. These findings corroborate anatomical evidence from monkeys showing an enhanced PI-MT pathway following an early-life lesion of V1, compared to adults.

Photopic Negative Response Obtained Using a Handheld Electroretinogram Device: Determining the Optimal Measure and Repeatability.

PURPOSE: To determine the measure of the photopic negative response (PhNR) of the full-field electroretinogram (ERG) that exhibits the optimal level of test-retest repeatability, and examine its repeatability under different conditions using a handheld, nonmydriatic ERG system and self-adhering skin electrodes. METHODS: Multiple ERG recordings (using 200 sweeps each) were performed in both eyes of 20 normal participants at two different sessions to compare its coefficient of repeatability (CoR; where 95% of the test-retest difference is expected to lie) between different PhNR measures and under different testing conditions (within and between examiners, and between sessions). RESULTS: The ratio between the PhNR trough to b-wave peak and b-wave peak to a-wave trough amplitude (PhNR/B ratio) exhibited the lowest CoR relative to its effective dynamic range (30 ± 4%) when including three recordings. There were no significant changes in the PhNR/B ratio over seven measurements (4 right and 3 left eyes) at either session (P ≥ 0.100), or significant difference in its CoR between different testing conditions (P = 0.314). CONCLUSION: The PhNR/B ratio was the measure that minimized variability, and its measurements using a novel handheld ERG system with self-adhering skin electrodes and the protocols described in this study were comparable under different testing conditions and over multiple recordings. TRANSLATIONAL RELEVANCE: The PhNR can be measured for clinical and research purposes using a simple-to-implement technique that is consistent within and between visits, and also between examiners.

Measuring the Photopic Negative Response: Viability of Skin Electrodes and Variability Across Disease Severities in Glaucoma.

PURPOSE: The purpose of this study was to determine the feasibility of measuring the photopic negative response (PhNR) of the full-field electroretinogram (ERG) using skin electrodes compared to conjunctival electrodes and its test-retest variability over a range of disease severities in open-angle glaucoma. METHODS: Recordings were performed twice (100 sweeps each) within the same session in 43 eyes of 23 participants with glaucoma to determine its intrinsic variability. The ratio between the PhNR and B-wave amplitude (PhNR/B ratio) was determined for each trace and computed across 5 to 100 sweeps of each recording. Spectral-domain optical coherence tomography was used to measure the average peripapillary retinal nerve fiber layer (RNFL) thickness. RESULTS: The PhNR/B ratio and its magnitude of variability were not significantly different between skin and conjunctival electrodes (P ≤ 0.197), and the degree of variability decreased substantially with increasing number of sweeps. For skin electrodes, the intraclass correlation coefficient was 0.89 and 0.91 for right and left eyes, respectively. The variability of the PhNR/B ratio decreased with lower RNFL thickness values and larger B-wave amplitudes (P ≤ 0.002). CONCLUSIONS: Skin electrodes are a viable alternative to conjunctival electrodes when measuring the PhNR in open angle glaucoma, and increasing the number of sweeps substantially reduced its intrinsic variability; the extent of variability was also lower with worsening disease severity. TRANSLATIONAL RELEVANCE: The feasibility of performing ERG recordings widely across a range of disease severities in glaucoma can be achieved through using skin electrodes and increasing the number of sweeps performed to improve measurement repeatability.

Application-Dedicated Selection of Filters (ADSF) using covariance maximization and orthogonal projection.

Visible and near-infrared (Vis-NIR) spectra are generated by the combination of numerous low resolution features. Spectral variables are thus highly correlated, which can cause problems for selecting the most appropriate ones for a given application. Some decomposition bases such as Fourier or wavelet generally help highlighting spectral features that are important, but are by nature constraint to have both positive and negative components. Thus, in addition to complicating the selected features interpretability, it impedes their use for application-dedicated sensors. In this paper we have proposed a new method for feature selection: Application-Dedicated Selection of Filters (ADSF). This method relaxes the shape constraint by enabling the selection of any type of user defined custom features. By considering only relevant features, based on the underlying nature of the data, high regularization of the final model can be obtained, even in the small sample size context often encountered in spectroscopic applications. For larger scale deployment of application-dedicated sensors, these predefined feature constraints can lead to application specific optical filters, e.g., lowpass, highpass, bandpass or bandstop filters with positive only coefficients. In a similar fashion to Partial Least Squares, ADSF successively selects features using covariance maximization and deflates their influences using orthogonal projection in order to optimally tune the selection to the data with limited redundancy. ADSF is well suited for spectroscopic data as it can deal with large numbers of highly correlated variables in supervised learning, even with many correlated responses.

Test-Retest Variability of Fundus-Tracked Perimetry at the Peripapillary Region in Open Angle Glaucoma.

PURPOSE: To examine the association between the measured level and local gradient of visual sensitivity on the magnitude of test-retest variability of its measurements at the peripapillary region using fundus-tracked perimetry in eyes with glaucoma. METHODS: A total of 30 participants with open angle glaucoma underwent three examinations in one eye on fundus-tracked perimetry using a stimulus pattern that sampled the peripapillary region densely. Factors associated with the magnitude of test-retest variability at each location were examined. RESULTS: There was no significant change in average pointwise sensitivity (PWS) between tests 1 and 2 (P = 0.855), but a significant reduction between tests 2 and 3 (P < 0.001). Therefore, all subsequent analyses were performed only between tests 1 and 2. Multivariate analyses revealed that the magnitude of test-retest variability at a given location was significantly associated with its average sensitivity and gradient of sensitivity relative to the immediately adjacent locations (P ≤ 0.001), meaning that locations with low levels of sensitivity (4-18 dB) with low gradients of sensitivity (<2 dB/location) had a 90% test-retest limit of ±5.83 dB, compared to a limit of ±10.65 dB in areas of high gradients of sensitivity (>4 dB/location). CONCLUSIONS: On a pointwise basis, the test-retest variability of visual sensitivity in glaucoma is not just related to its measured level, but also its local gradient when using fundus-tracked perimetry. Locations with low sensitivity do not necessarily demonstrate very high test-retest variability, depending on the local uniformity of visual field damage.

Vitamin A Deficiency Presenting with 'Itchy Eyes'.

We present the case of an 88-year-old female living in metropolitan Melbourne, Australia who developed vitamin A deficiency manifesting as 'itchy eyes' due to a bizarre dietary habit. Slit lamp examination revealed Bitot's spots and a subsequent vitamin A serum level test revealed severe deficiency. An electroretinogram showed grossly reduced a- and b-wave amplitudes consistent with generalised rod and cone dysfunction - these parameters showed marked improvement 5 months post supplementation. This case highlights the presence of vitamin A deficiency in the developed world and that a careful dietary history should be taken when assessing a patient complaining of 'itchy eyes'. Timely diagnosis and treatment may result in dramatic resolution of symptoms and signs as well as prevention of serious morbidity.