Sub-pixel rendering for supra-threshold visual field testing
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Solution Overview
Problem
Current supra-threshold vision tests, such as the Moorfields Motion Displacement Test, face challenges with unreliable responses due to false negatives, increased test duration, and limitations in measuring visual sensitivity across the field of vision, especially in young individuals with high retinal ganglion cell density, and difficulties in tracking visual sensitivity progression over time.
Innovation Solution
The method involves a supra-threshold test strategy that uses cluster analysis based on optic nerve fibre bundles to determine retesting locations, adjusts stimulus intensity, and employs sub-pixel rendering on LCD monitors to improve sensitivity and accuracy, allowing for more reliable and efficient testing by reducing the number of retests and increasing the precision of motion displacement threshold measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retest strategy is used to reduce false negatives, then reliability is improved, but test duration increases
Solution Approach 1:
The patent applies partial retesting by selecting only certain locations for retesting based on confidence thresholds rather than retesting all locations. Locations with high confidence values (above threshold) are not retested, while locations with low confidence values are selected for retesting. This partial action approach reduces the number of retests needed compared to comprehensive retesting, thereby shortening test duration while still improving reliability by addressing the most uncertain measurements.
2Measurement precision
If stimulus intensity is increased to improve detection, then measurement precision is improved, but false positive rate increases
Solution Approach 1:
The patent dynamically adjusts stimulus intensity based on individual subject characteristics, particularly retinal ganglion cell density estimates. For subjects with high RGC density (younger individuals), lower stimulus intensities are used, while subjects with lower RGC density receive higher intensities. This parameter adaptation allows precise measurement of visual sensitivity for each subject without universally increasing intensity, thereby maintaining measurement precision while minimizing false positives across different population groups.
Solution Approach 2:
The system uses confidence values calculated from multiple presentations at each location to feedback-adjust testing parameters. Locations with intermediate confidence values (neither clearly seen nor clearly unseen) trigger retesting with adjusted parameters. This feedback mechanism allows the system to identify and retest only the ambiguous cases, improving overall measurement precision while avoiding unnecessary retesting of clear cases that would increase false positives.
3Measurement precision
If conventional pixel rendering is used, then device complexity is reduced, but measurement precision is limited by pixel resolution
Solution Approach 1:
The patent employs sub-pixel rendering that exploits the vertical arrangement of sub-pixels within each pixel column. By selectively activating individual sub-pixels (e.g., top, middle, or bottom sub-pixel) within a pixel column, the system achieves vertical positioning precision finer than the pixel grid. This dimensional exploitation of sub-pixel structure allows motion displacement thresholds to be measured with precision below one pixel height, overcoming the resolution limit of conventional pixel rendering without requiring additional display hardware.
4Measurement precision
If the number of test locations is increased to improve coverage, then measurement precision is improved, but test duration increases
Solution Approach 1:
The patent performs preliminary estimation of retinal ganglion cell density and confidence value calculation before determining the final test protocol. By pre-calculating which locations are likely to provide meaningful information based on anatomical maps and initial confidence assessments, the system can optimize the set of test locations to maximize visual field coverage with the minimum necessary number of measurements. This preliminary action prevents unnecessary testing at locations that would not contribute significantly to measurement precision.
Solution Approach 2:
The testing protocol is dynamically adapted based on individual subject characteristics and real-time performance. The system adjusts the number and distribution of test locations according to estimated RGC density, age-related factors, and initial test results. For subjects with high RGC density where smaller displacements are detectable, the system can use fewer locations with finer displacement steps. This dynamic optimization maintains comprehensive visual field coverage while adjusting test duration to match individual needs rather than applying a fixed lengthy protocol to all subjects.
Data Source
AI summary
One embodiment of the invention provides a method for performing a supra-threshold test of sensitivity across a visual field of a subject. The method includes presenting a stimulus at each location of a set of locations spread across the visual field and obtaining for each stimulus a result indicating whether or not the stimulus was seen by the subject. The method further includes determining for each location whether or not to re-present a stimulus at that location, wherein for a given location, the determining involves combining results obtained from multiple locations. These multiple locations are defined by a cluster associated with the given location, with the cluster being determined based on the paths of optic nerve fibre bundles across the visual field.