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This 10-year-old boy has had an exodeviation as seen here since birth. He is otherwise healthy and active. Motility examination is shown in the pictures. He has a moderate exodeviation in primary position with right upper lid ptosis. Elevation, depression and adduction are limited in the right eye. The ptosis on the right decreases when the eye is looking down. The right upper lid is retracted on levoversion. Visual acuity is OD 20/200 and OS 20/20. Refraction is OD +1.50 –1.00 X 60 and OS +2.50 -.50 X 100. The right pupil is dilated and reacts sluggishly. Media are clear, and the fundus is normal in both eyes. The boy has no complaints and denies diplopia.

1.	The most likely diagnosis is:
	d -- congenital third nerve palsy This boy has had strabismus since birth.  He has limited elevation, depression, and adduction in the right eye, the pupil is dilated in that eye and he has ptosis of the right upper lid in the primary position.  These all point to a diagnosis of congenital third nerve palsy.
2.	Which eye muscle(s) function essentially normally in the right eye according to the pictures?
	b -- lateral rectus The only muscle in the right eye that is functioning essentially normally is the sixth nerve innervated lateral rectus.  The right superior oblique innervated by the fourth nerve is probably innervated by its action and is probably eliminated by co-contraction of the vertical recti on downgaze.
3.	The right upper lid function is influenced by:
	e -- all of the above The right upper lid has some innervation from its usual source because the ptosis is not complete. However the right levator palpebri overacts in levoversion from aberrant regeneration from the nerve to the medial rectus.  The third nerve is innervating the eye muscles it usually does, but not in the normal way.  The position of the eye and the lid of this right eye is highly dependant on the direction of gaze (innervation of specific muscles).