Dynamic Velocity Threshold Filter for Optokinetic Nystagmus Noise Removal
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Solution Overview
Problem
Conventional optokinetic nystagmus testing in clinical environments is hindered by non-OKN activities, head movements, blinks, and random signal noise, leading to false judgments, especially in young children, where unrestrained head movement is challenging without a headset, and fixed velocity thresholds fail to accurately distinguish slow and quick phases due to significant noise and spikes.
Innovation Solution
A dynamic velocity threshold (DVT) filter is introduced, varying from minimum to maximum thresholds, using linear regression, standard deviation, and F statistics to identify slow phases and remove noise, thereby providing a more reliable quantitative assessment of visual acuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed velocity threshold filter is used to identify slow and quick phases in optokinetic responses, then the identification process is simple, but the accuracy deteriorates due to random noises, spikes, and drifts in the OKN response
Solution Approach 1:
The patent applies a dynamic velocity threshold that adapts to the actual signal characteristics rather than using a fixed threshold. The threshold is calculated based on the standard deviation of the velocity signal, allowing it to dynamically adjust to different noise levels and signal conditions, thereby improving identification accuracy while maintaining reasonable complexity
Solution Approach 2:
The system uses feedback by continuously monitoring the velocity signal characteristics and adjusting the threshold accordingly. The threshold calculation incorporates the standard deviation of the velocity signal, creating a feedback mechanism that adapts to changing signal conditions and improves robustness against noise and artifacts
2Ease of operation
If conventional optokinetic testing is performed without head restraint in young children, then the ease of operation improves, but the reliability deteriorates due to head movements and spurious eye movements
Solution Approach 1:
The patent extracts and removes artifacts and non-OKN activities from the eye movement signal through sophisticated processing algorithms. By identifying and eliminating head movement artifacts and spurious eye movements, the system isolates the true optokinetic response, maintaining reliability without requiring head restraint
Solution Approach 2:
The system uses an intermediary processing layer that distinguishes between true OKN responses and artifacts. The algorithms act as intermediaries to interpret the complex signal, separating genuine eye tracking movements from head movements and other spurious activities, thereby enabling reliable measurement in unrestrained children
3Measurement precision
If the velocity threshold is set to remove quick phases, then the quick phases are effectively filtered, but random noises and spikes are not distinguished and remain in the signal
Solution Approach 1:
The patent applies local quality by using different processing criteria for different portions of the velocity signal. The dynamic threshold and artifact detection algorithms treat different signal characteristics differently, removing quick phases while preserving and identifying true OKN slow phases, and eliminating random noises and spikes through localized analysis of signal properties
Data Source
AI summary
Optokinetic nystagmus (OKN) is an eye movement elicited by the tracking of moving objects in a visual field. It is characterized by an alternating smooth pursuit in one direction and saccadic movement in the other direction. The presence or absence of OKN indicates whether or not the moving stimulus was visible to the observer, without the explicit cooperation of the observer. It can be a tool for objective visual acuity assessment for patients such as young children who lack cognitive, attentional and language capabilities. Since the patient's head movement and unstable eye gaze may occur during the test, which often brings noises and irrelevant activities in the responses, making recognition of presence/absence of the OKN a challenging task. The present invention, using a dynamic velocity threshold (DVT) filter, provides a system and method for a quick and reliable OKN test and quantitative assessment of visual acuity.