Questions:
21. What are 5 clinical settings where OKN testing may be helpful?
22. Why should OKN testing be done in infants suspected of having the infantile nystagmus syndrome (congenital nystagmus)?
23. Where is the lesion likely to be located in a patient with homonymous hemianopia and symmetric OKN?
24. Where is the lesion likely to be located in a patient with homonymous hemianopia and asymmetric OKN response?

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Questions with answers:
21. What are 5 clinical settings where OKN testing may be helpful?
    1. OKN response confirms the presence of 20/400 or better VA in infants, very young children, and patients suspected of nonorganic visual loss claiming to have a visual acuity of hand motion, light perception, or no light perception.
    2. In infantile nystagmus, a preserved vertical OKN response indicates intact vision and there is typically a reverse response to horizontal OKN testing.
    3. Homonymous hemianopia (reduced OKN response when moving the OKN tape in the direction of a parietal lobe lesion).
    4. OKN is also helpful to elicit subtle adduction weakness in internuclear ophthalmoplegia.
    5. To elicit convergence retraction nystagmus of the dorsal midbrain syndrome (rotate the drum downward).

22. Why should OKN testing be done in infants suspected of having the infantile nystagmus syndrome (congenital nystagmus)?
Confirm the diagnosis: a reverse OKN response is characteristic of infantile nystagmus syndrome and to check for intact vision: a preserved vertical OKN = intact vision.

23. Where is the lesion likely to be located in a patient with homonymous hemianopia and symmetric OKN?
Probably in the occipital lobe (most likely vascular), but can be in the temporal lobe.

24. Where is the lesion likely to be located in a patient with homonymous hemianopia and asymmetric OKN response?
The lesion would probably deep in the parietal lobe (most likely mass). There is a reduced response when OKN tape is moved in the direction of the lesion.

The information below is from Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme

1.11 Ocular Motility
The motility examination evaluates the integrity of the following:
● Extraocular muscles
● Neuromuscular junction
● Ocular motor nerves (third, fourth, and sixth)
● Ocular motor nuclei
● Internuclear pathways
● Supranuclear pathways

The ocular motility examination consists of the following:
● Observation in primary gaze
● Ductions (monocular eye movements)
● Vergence (binocular dysconjugate movements)
● Versions (binocular conjugate eye movements)
  ○ Saccades○ Pursuit
  ○ Oculocephalic responses and vestibulo-ocular reflex (VOR)
  ○ Optokinetic nystagmus
● Detection and measurement (with prisms) of ocular misalignment (strabismus)
● Detection of nystagmus

The various techniques used to examine the extraocular movements, how to interpret abnormal extraocular movements, and their localization value are detailed in Chapter 13.
An optokinetic stimulus produces a jerk nystagmus in patients with good vision and intact ocular motor systems. It coordinates eye movements when the environment moves, such as when looking out from a moving train.
Physiologic optokinetic nystagmus (OKN) can be elicited by rotating a striped drum or moving a striped tape horizontally and vertically and asking the patient to “count the stripes as they go by” (▶Fig. 1.27).

The slow phases of the OKN are generated as the patient follows a target. The OKN fast phase is a corrective saccade to view the next target.

The OKN response is involuntary and is difficult to suppress. An intact OKN response confirms that visual acuity is at least 20/400. This is very helpful in checking the vision of infants and very young children as well as patients suspected of nonorganic visual loss claiming to have a visual acuity of hand motion, light perception, or no light perception. ▶Table 1.4 outlines when to test for OKN and why. Testing the OKN is also helpful to elicit subtle adduction weakness in internuclear ophthalmoplegia and convergence retraction nystagmus of the dorsal midbrain syndrome (rotate the drum downward).nonorganic visual loss claiming to have a visual acuity of hand motion, light perception, or no light perception. ▶Table 1.4 outlines when to test for OKN and why. Testing the OKN is also helpful to elicit subtle adduction weakness in internuclear ophthalmoplegia and convergence retraction nystagmus of the dorsal midbrain syndrome (rotate the drum downward).

1.12 Visual Field Testing
Examination of the visual field is essential in all patients complaining of visual loss. It can be performed at bedside using confrontation techniques and Amsler grid testing. Formal visual field visual fields, how to interpret a visual field test, and the localization value of visual field defects are detailed in Chapter 3.

1.13 Symmetry of Red Reflex
The red reflex is examined with the ophthalmoscope (see Chapter 2). A normal or symmetric red reflex suggests transparency of the ocular media (▶Fig. 1.28).

Symmetry of a normal red reflex suggests the following:
● Symmetric transparency of the ocular media
● Symmetric refraction and no strabismus
● Grossly attached retina testing requires machines that are available in most ophthalmic clinics and in all neuro-ophthalmology offices. The various techniques used to test

1.14 Funduscopic Examination
The ocular fundus can be viewed directly through the pupil with the help of an ophthalmoscope. Pupillary dilation is essential because it allows easier and better visualization of the fundus (see Chapter 2). However, new digital fundus cameras allow excellent quality photographs without dilation of the pupils (nonmydriatic digital cameras). Such cameras are now often routinely used in nonophthalmic settings to visualize the ocular fundus.

Examination of the fundus includes the following:
● Optic nerve
  ○ Normal (measure cup-to-disc ratio)
  ○ Pale
  ○ Swollen
● Macula and retina
  ○ Normal
  ○ Whitening from edema
  ○ Exudates
  ○ Hemorrhages
  ○ Detachment
  ○ Hole
  ○ Mass
● Arteries
● Veins
● Vitreous

The best three-dimensional views of the optic nerve are obtained with lenses and a slit lamp. This technique requires cooperation from the patient and is mostly used in a neuro-ophthalmologist’s or ophthalmologist’s office.

1.15 General Examination
Depending on the type of complaints, a neurologic examination, including cranial nerves, and general examination, including blood pressure, will complete the neuro-ophthalmic examination.

Reference: 1. Neuro-ophthalmology Illustrated-2nd Edition. Biousse V and Newman NJ. 2012. Thieme

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