The Worth 4-Dot Test (W4D test) is a simple clinical test used in binocular vision assessment. It helps to check whether a patient is using both eyes together (binocular single vision), or whether one eye is being suppressed or the patient has diplopia (double vision). --- Principle: Uses four lights arranged as: 1 red (top) 2 green (left and right sides) 1 white (bottom) The patient wears red-green goggles (red filter over Right eye, green over the left eye ). --- Interpretation: Normal binocul