Evaluation of green filter leakage in the Worth 4 Dot test: Implications for clinical accuracy

Dear Editor, The Worth 4 Dot Test is a widely used clinical tool for assessing binocular vision, particularly suppression, diplopia, and anomalous retinal correspondence (ARC). Introduced by Claud Worth in 1903, it remains a key method for detecting unilateral suppression while both eyes view simultaneously.[1–3] The test uses red-green glasses to present four dots—two green, one red, and one white—helping clinicians detect binocular vision anomalies like suppression and diplopia. While accurate filter performance is essential for test reliability, limited research has examined the quality of these filters and their impact on accuracy. A previous study observed that red and green filters introduce artifacts that can impact performance in binocular vision tests.[4] Our study investigates green filter leakage, a potential flaw that could lead to misinterpretations in clinical assessments. We conducted a pilot study in Bangalore to assess the performance of red and green filters using 25 trial boxes across two hospitals and 23 optical centers. For near assessment, the Worth 4 Dot torch was placed 33 cm from the mobile (Samsung A34) rear light source, while for the far evaluation, the Worth 4 Dot box was positioned 6 m away. The mobile rear flashlight provided illumination during the assessment. For near testing, a red filter was placed in front of the flashlight, and images of the Worth 4 Dot torch were captured. The red filter was then replaced with a green filter, and the process was repeated. For far testing, the same procedure was followed using the Worth 4 Dot box, with images captured using the mobile camera. A total of 50 images (25 near, 25 far) were analyzed for filter leakage and compared to expected results: two red dots with the red filter and three green dots with the green filter placed in front of the camera. Our findings revealed a significant issue with green filter leakage, which was observed in 88% (44/50) of the captured images. While the red filter functioned correctly in all cases, the green filter failed to fully block red light. This resulted in an unintended extra red dot appearing in the images, which could distort clinical interpretations. Notably, this issue was present in 22 of the 25 trial boxes, suggesting that variability in filter quality may not be limited to specific manufacturers but could be a common issue. Fig. 1 highlights both the correct red filter performance and the deviations due to green filter leakage.Figure 1: Observed results from the Worth 4 Dot Test demonstrating filter performance. (a) Two red dots observed when a red filter is placed in front of the camera, confirming proper filter function. (b) Green filter leakage showing three green dots and one red dot when a green filter is placed in front of the camera. This leakage was observed in 44 out of 50 images, indicating a significant technical issue with the green filter’s performanceThese findings reveal a critical flaw in the green filter, potentially affecting diagnostic accuracy. While effective for normal binocular vision and left eye suppression, leakage raises concerns for right eye suppression. Clinicians must be aware of this issue and conduct regular quality checks. Improved filter manufacturing and further research are essential to enhance test reliability and minimize errors in clinical assessments.

Abstract licence: CC BY-NC-SA

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