Questions:
11. Which 5 features of pupil function should be documented in a neuro-ophthalmic examination?
12. Would a Relative Afferent Pupillary Defect be expected with anisocoria?
13. Does an occipital lobe injury result in a Relative Afferent Pupillary Defect?
14. Does a unilateral optic neuropathy result in a Relative Afferent Pupillary Defect?
15. Can a unilateral optic tract lesion result in a Relative Afferent Pupillary Defect?
16. What anatomic factor explains the Relative Afferent Pupillary Defect with an optic tract lesion?
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Questions with answers:
11. Which 5 features of pupil function should be documented in a neuro-ophthalmic examination?
1. Size of pupils
2. Presence or absence of anisocoria in light and dark
3. Response to light
4. Presence or absence of a relative afferent pupillary defect
5. Response to near fixation
12. Would a relative afferent pupillary defect be expected with anisocoria?
No
13. Does an occipital lobe injury result in a relative afferent pupillary defect?
No
14. Does a unilateral optic neuropathy result in a relative afferent pupillary defect?
Yes
15. Can a unilateral optic tract lesion result in a relative afferent pupillary defect?
Yes
16. What anatomic factor explains the relative afferent pupillary defect with an optic tract lesion?
The nasal fibers of the ipsilateral eye (53% of all fibers) cross in the chiasm to join the uncrossed temporal fibers (47% of all fibers) of the contralateral eye. Because more fibers in the optic tract come from the opposite eye (crossed fibers), a relative afferent pupillary defect is often observed in the eye contralateral to an optic tract lesion.
The information below is from Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme
1.9 Pupillary Testing
Pupils should be tested in the dark with a bright light and with the patient fixating at a distance (▶Fig. 1.16).
Pupil examination includes the following (▶Table 1.3):
● Size
● Presence of anisocoria (difference of size between the two pupils)
● Response to light
● Presence of a relative afferent pupillary defect (RAPD)
● Dilation in the dark
● Constriction at near
For a full discussion on the pupil, see Chapter 12.
1.9.1 Relative Afferent Pupillary Defect
A RAPD (▶Fig. 1.17 and ▶Fig. 1.18) ipsilateral to visual loss indicates an optic neuropathy or severe retinal disease (in which case the retina looks abnormal on funduscopic examination). Ocular diseases, such as corneal abnormalities, cataracts, and most retinal disorders, do not cause RAPDs.
Pathophysiology of the RAPD includes the following:
1. When a light is directed into either eye, both pupils react equally. The brighter the light source, the greater the degree of bilateral pupillary constriction.
2. The amount of pupillary constriction from the same light source directed to either eye should be identical.
3. In unilateral optic nerve (or retinal ganglion cell) dysfunction, the light signal received by the brainstem efferent centers is relatively less than when the same light source is presented to the unaffected eye. Hence, both pupils constrict less when the involved eye is stimulated and more when the normal eye is stimulated.
4. A RAPD will not cause anisocoria.
Testing for a RAPD includes the following:
1. The swinging flashlight test demonstrates a relative afferent pupillary defect in patients with unilateral or asymmetric optic neuropathies (Marcus Gunn pupil):
● Swinging the light source back and forth emphasizes this difference in transmission of the afferent signal because both pupils will reset at the size appropriate for the amount of light transmitted by the illuminated optic nerve.
● When the light source swings from the affected eye to the unaffected eye, further constriction of both pupils will be demonstrated; when the light swings back to the involved eye, relative dilation of both pupils will occur. Even though the examiner may look only at the pupil upon which the light is shining, it is important to be aware that both pupils are changing size equally during this maneuver.
2. By placing neutral density filters over the normal eye, the examiner can neutralize the RAPD and quantitate its severity (▶Fig. 1.19).
Reference: 1. Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme
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