1. Measure the pupil distance and select a trial frame that is consistent with the pupil distance; 2. The refractive error of the examinee's eyes is completely corrected; 3. Insert the Maddox rod lens insert in front of the examinee's right eye so that the Maddox rod lens grid are in the horizontal direction; 4. Place the near Torrington board 40cm in front of the eyes, turn on the light source, and make the light point of the light source level with of sight; 5. Ask the examinee about the position relationship between the light and the red vertical line; Note: 2x AA batteries are not included in the shipment, you need to prepare them yourself Colour:White Material:ABS Package Contents: 1 x Strabismus Detection Tool 1 x Stand Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.