Looking at a nearby target causes vergence, accommodation and miosis (ie, the convergence reaction). The convergence reaction is disturbed in rostral midbrain lesions and tumors of the pineal region and thalamus, which are also often associated with abnormalities of vertical gaze and result in Parinaud's syndrome.

Lesions of these regions are also often associated with convergence-retraction nystagmus. Note that this is not a true form of nystagmus because it lacks slow phases. This condition results from co-contraction of the extraocular muscles on attempted upgaze. The medial rectus muscles are the most powerful of the extraocular muscles, and their contraction produces convergent movements even when all other extraocular muscles are contracting. The cocontraction of all extraocular muscles causes retraction of the globe into the orbit.

Convergence-retraction nystagmus localizes the disease process to the dorsal midbrain and is part of dorsal midbrain syndrome.

This can be provoked by inducing upward saccades or by looking at a moving optokinetic drum with its stripes going downward. Instead of vertical saccades, rapid convergent eye movements that are associated with retractions of the eyeball occur.

Tonic downward deviation of the eyes combined with retraction of the eyelids, referred to as the setting sun sign, is primarily observed in children as part of a dorsal midbrain syndrome. Conjugate paresis of upgaze is an associated finding, and in these cases, the doll’s head maneuver cannot induce upward movements of the eyes.

Pathogenesis
The cause is damage to the posterior commissure¹ and projecting fibres from the interstitial nucleus of Cajal².

Causes
The common causes are pineal tumour and hydrocephalus.
The syndrome may also be due to drugs such as barbiturates, neuroleptics, and carbamazepine.

• Diminished upward saccades
• Vertical gaze palsy
• Convergence retraction nystagmus on attempted upward saccades (or when viewing a down-moving OKN tape)
• Light-near dissociation

Lesions of the posterior commissure usually affect all types of eye movements, although the vertical VOR and Bell’s phenomenon (upward eye deviation during lid closure) can be spared³.
Pineal tumors may affect the proximal course of both CNs IV by compressing the tectum of the midbrain

Other features include:

• Skew deviation
• Fixation instability (square-wave jerks)
• Convergence spasm
• Divergence paralysis
• Irregular pupils
• Pseudo-abducens palsy (a slower moving abducting eye during horizontal saccades, perhaps related to convergence excess).
• Downward gaze preference (setting sun sign: typically when the syndrome is acute).
• Downbeating nystagmus
• Abnormalities of vertical smooth pursuit and VOR eye movements

More isolated lesions can produce limited syndromes such as upgaze or downgaze palsies.  The saccadic gaze palsy is likely due to involvement of projecting fibers from the INC².

Upgaze and downgaze palsies can occur with or without the preservation of VOR-induced vertical eye movements, depending on whether the INC, which is the midbrain centre for vertical VORs, is affected.  

(vv)Hpim Pparinaud-13.mp4(tt)

(vv)Dorsal Midbrain.mp4(tt)

From: Karanth A. Dorsal midbrain syndrome. Retrieved from: http://ophthalclass.blogspot.com/https://www.youtube.com/watch?v=u7D1-zj98l8