Self-test for distortion

With reading spectacles on if you need them, cover one eye and align the uncovered eye to the centre of the cross. Move toward the screen until one of the red dots disappears. Keep looking at the centre of the cross and you should see an array of small squares with straight edges. If there is a patch of missing or gray vision or if the lines appear kinked while you maintain your fixation at the centre of the X then you need to see your general practioner, optician or ophthalmologist sooner rather than later ie withing days rather than weeks.