If in a patient of acoustic neuroma, corneal reflex is absent it implies involvement of cranial nerve:
(a) 5th(Ref. Scott Brown, 8th ed., Vol 2 page 1370)In corneal reflex the sensory afferent part of the reflex arc is trigeminal and motor efferent part is facial nerve.The involvement of 5th nerve, at the upper pole in CP angle by acoustic neuroma is manifested as a loss of corneal reflex.Facial nerve being mainly a motor nerve therefore is resistant to compression. The motor fibres of Facial nerve take a very long time to get affected hence facial weakness is seen quiet late in acoustic neuroma. So loss of corneal reflex in acoustic neuroma, initially and largely, is due to involvement of the sensory efferent element of the reflex arc, i.e. 5th nerve. Technically involvement of motor aspect of facial nerve occurring late in the course of Acoustic neuroma will also contribute to loss of corneal reflex but better signs for looking facial nerve involvement, i.e. the signs eliciting facial muscle movements will now be there.Corneal reflex is done primarily to check 5th nerve involvement. This reflex should be elicited carefully avoiding injury to the cornea.
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Acoustic Neuroma