Many years ago I noticed I was having eye tremors. Of course back then I didn’t know the issue was called an eye tremor rather I thought it was a muscle spasm in my eye. When I was deeply focused when reading or sewing my eyes would jump, jump, jump. To begin with I looked up to see what was going on. Over time I learned to stay focused as if nothing was happening and my vision would align if I did not respond to the movement. Later I researched the topic and discovered that such undesired movement in the eye can be eye tremors or nystagmus due to multiple sclerosis.
To learn more about the eye tremors look-up: http://www.webmd.com/multiple-sclerosis/guide/managing-related-tremors, http://www.nationalmssociety.org/Symptoms-Diagnosis/MS-Symptoms/Tremor and http://www.nationalmssociety.org/Symptoms-Diagnosis/MS-Symptoms/Vision-Problems. Image from www.creationstudies.org.