Presentation
Though present from birth, symptoms of congenital fourth cranial nerve palsy may start as subtle and increase with age. Hence, diagnosis by a healthcare practitioner may not be made until later childhood or adulthood. Young children adopt a compensatory head position in order to compensate for the underacting superior oblique muscle. The characteristic head tilt is usually away from the affected side to reduce eye strain and prevent double vision (diplopia). Old photographs may reveal the presence of a consistent head tilt (ocular torticollis) from an early age. Most patients with congenital CN IV palsy have facial asymmetry due to the chronic head tilt. Other compensatory measures for congenital fourth nerve palsy are development of large vertical fusional amplitudes and lack of subjective symptoms of torsion, even in the presence of great ocular rotation.
Congenital fourth nerve palsy may remain undetected until adulthood, when intermittent diplopia may arise, due to decompensated ability to overcome the vertical deviation. Until this occurs, many ophthalmologists and optometrists may miss the other signs and symptoms. Reduced vertical fusional reserves result from fatigue (stress, fever, other illnesses, a lot of near work) or simply the effects of old age. Diplopia from congenital fourth nerve palsy has occasionally been reported to manifest transiently during pregnancy. Congenital fourth nerve palsy may also become evident following cataract surgery once binocular vision is restored after a long period of progressive monocular visual loss and accompanying vergence decompensation. Other adult patients complain of neck pain, after years of chronic head tilting (ocular torticollis).
Congenital fourth nerve palsy can affect reading comprehension (and concentration during other near tasks) due to the increased vertical fusional demands and head tilting required to maintain single vision and prevent vertical diplopia. Some patients find they lose their place easily while reading, and find a marker or using a finger to guide them helpful.
Read more about this topic: Congenital Fourth Nerve Palsy
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