There is an image of your face in the upper right corner of the screen. Please check it before the test to make sure your eyes are well lit and clearly visible. If you are wearing glasses, make sure there is no glare on the lenses that obscures your eyes.
Take the test in a well-lit room. Use a table lamp to clearly illuminate your face, if possible. If you are wearing glasses, avoid sitting facing a window, as this can cause additional glare on your lenses.