"I am a general ophthalmologist. One of my patient[s] complains of vertical diplopia only in certain position[s] of gaze (a mid-accommodated position). There is no tilt of images. I am not able to detect any vertical or horizontal deviation, [nor] movement restriction in any direction. He is a recently detected diabetic and hypertensive. He does not complain of any neurological symptoms. Can this be a skew deviation? Should I be more aggressive in investigating for a neurological cause for his symptom?"

Statistically this should be an acquired superior oblique palsy, but a very slight one.  My suggestion is to have the patient look in the direction where diplopia is noticed.  Then you should introduce vertical prism until the diplopia disappears.  I suspect it will take no more than a few prism diopters.  If the diplopia is gone in all fields, you may have to reduce it some, then give the person temporary prism (Fresnel) and check him in a week. In the meantime he should see his internist about the diabetes. The red glass test is a good way to map the diplopia.  You should check him in gaze side to side and then with the head tilted to either side. If this is from diabetes or other mild neurologic deficit, it should go away in a few weeks to months.     Eugene M. Helveston, MD