halogen penlight used to observe<unk> .<unk>  provides a useful diagnostic tool for testing the integrity of the sensory and motor functions of the eye. Emergency physicians routinely test<unk>  to assess brain stem function. Abnormal<unk>  reflex can be found in optic nerve injury, oculomotor nerve damage, brain stem lesion (including brain stem death), and depressant drugs, such as barbiturates. Examples are provided as below: *Optic nerve damage on the left (e.g. transection of left optic nerve, CN II, somewhere between retina and optic chiasma, therefore damaging the left afferent limb, leaving the rest of the<unk>  neural pathway on both sides intact) will have the following clinical findings: *The left direct reflex is lost. When the left eye is stimulated by<unk> , neither pupils constrict. Afferent signals from the left eye cannot pass through the transected left optic nerve to reach the intact efferent limb on the left. *The<unk>  consensual reflex is lost. When left eye is stimulated by<unk> , afferent signals from the left eye cannot pass through the transected left optic nerve to reach the intact efferent limb on the<unk> . *The<unk>  direct reflex is intact. Direct<unk>  reflex of<unk>  pupil involves the<unk>  optic nerve and<unk>  oculomotor nerve, which are both intact. *The left consensual reflex is intact. Consensual<unk>  reflex of left pupil involves the<unk>  optic nerve and left oculomotor nerve, which are both undamaged. *Oculomotor nerve damage on the left (e.g. transection of left oculomotor nerve, CN III, therefore damaging the left efferent limb) will have the following clinical findings: *The left direct reflex is lost. When the left eye is stimulated by<unk> , left pupil does not constrict, because the efferent signals cannot pass from midbrain, through left CN III, to the left<unk>  sphincter. *The<unk>  consensual reflex is intact. When the left eye is stimulated by<unk> , the<unk>  pupil constricts, because the afferent limb on the left and the efferent limb on the<unk>  are both intact. *The<unk>  direct reflex is intact. When<unk>  is shone into<unk>  eye,<unk>  pupil constricts. Direct reflex of the<unk>  pupil is unaffected, The<unk>  afferent limb,<unk>  CN II, and the<unk>  efferent limb,<unk>  CN III, are both intact. *The left consensual reflex is lost. When the<unk>  eye is stimulated by<unk> , left pupil does not constrict consensually.<unk>  afferent limb is intact, but left efferent limb, left CN III, is damaged. Lesion localization example For example, in a person with abnormal left direct reflex and abnormal<unk>  consensual reflex (with normal left consensual and normal<unk>  direct reflexes), which would produce a left Marcus Gunn pupil, or what is called left afferent<unk>  defect, by physical examination. Location of the lesion can be deduced as follows: # Left consensual reflex is normal, therefore segments 2, 4, and 7 are normal. Lesion is not located in any of these segments. #<unk>  direct reflex is normal, therefore segments 2, 6, and 8 are normal. Combining with earlier normals, segments 2, 4, 6, 7, and 8 are all normal. # Remaining segments where lesion may be located are segments 1, 3, and 5. Possible combinations and permutations are: (a) segment 1 only, (b) segment 3 only, (c) segment 5 only, (d) combination of segments 1 and 3, (e) combination of segments 1 and 5, (f) combination of segments 3 and 5, and (g) combination of segments 1, 3, and 5. # Options (b) and (c) are eliminated because isolated lesion in segment 3 alone or in segment 5 alone cannot produce the<unk>  reflex abnormalities in question. # A single lesion anywhere along segment 1, the left afferent limb, which includes the left retina, left optic nerve, and left pretectal nucleus, can produce the<unk>  reflex abnormalities observed. Examples of segment 1 pathologies include left optic neuritis (inflammation or infection of the left optic nerve), detachment of left retina, and an isolated small stroke involving only the left pretectal nucleus. Therefore, options (a), (d), (e), (f), and (g) are possible. # A combined lesion in segments 3 and 5 as cause of defect is very unlikely. Microscopically precise strokes in the midbrain, involving the left pretectal nucleus, bilateral Edinger-Westphal nuclei, and their interconnecting fibers, could theoretically produce this result. Furthermore, segment 4 shares the same anatomical space in the midbrain as segment 3, therefore segment 4 will likely be affected if segment 3 is damaged. In this setting, it is very unlikely that left consensual reflex, which requires an intact segment 4, would be preserved. Therefore, options (d), (f), and (g), which all includes segment 3, are eliminated. Remaining possible options are (a) and (e). # Based on the above reasoning, the lesion must involve segment 1. Damage to segment 5 may accompany a segment 1 lesion, but is unnecessary for producing the abnormal<unk>  reflex results in this case. Option (e) involves a combined lesion of segments 1 and 5. Multiple sclerosis, which often affects multiple neurologic sites simultaneously, could potentially cause this combination lesion. In all probability, option (a) is the answer. Neuro-imaging, such as MRI scan, would be useful for confirmation of clinical findings.
Pupillary light reflex
Vestibulo–ocular reflex
Moro reflex
Corneal reflex
Oculocardiac reflex
Red reflex
Ocular tilt reaction
Galant reflex