Nystagmus

Brief Discussion on Nystagmus

1. Nystagmus Maj Md Ferdous Islam FCPS Part 2 Trainee Dept of Ophthalmology CMH,Dhaka

2. Defination Nystagmus is an involuntary, rhythmic to and fro oscillation of the eyes 2 phases 1. slow drift from the target of interest 2. corrective saccade back to the target

3. Terminologies Amplitude Frequency Direction Null zone Pursuit / Saccade Conjugate / Dissociated Jerk / Pendular

4. Amplitude is the angular distance traveled during nystagmus (excursion of the nystagmus ) Low : less than 5 Degree Moderate: 5-15 Degree H igh : > 15 Degree Direction The fast component defines the direction of Nystagmus

5. Frequency is the number of to and fro movements in one second Slow : (1-2 Hz) Medium : (3-4 Hz) Fast: (5 Hz or more) Null zone Gaze location where nystagmus is minimal. Located in the gaze opposite the fast component

6. Pursuit /Saccade Pursuit eye movements allow the eyes to closely follow a moving object Saccades are quick , simultaneous movements of both eyes in the same direction

7. Conjugate/Dissociated Conjugate : nystagmus which is symmetric in direction, amplitude and rate Dissociated : when it differs in any one of the parameters between two eyes

8. Jerk / Pendular Jerk nystagmus Pendular nystagmus Alternation of slow phase drift rapid corrective saccade in opposite direction Sinusoidal oscillation with slow phase in both directions and no corrective saccade Direction of jerk nystagmus = direction of the fast phase Pendular nystagmus may be horizontal or vertical Right or left beating nystagmus Upbeat or downbeat nystagmus Not characterised by right, left, up, down beating as there is no fast phase

9. Alexanders law It states that the amplitude of jerk nystagmus is largest in the gaze of direction of fast component

10. Mechanism of nystagmus Foveal centration of an object of regard is necessary to obtain the highest level of visual acuity Three mechanisms are involved in maintaining foveal centration of an object of interest:  Fixation  The vestibulo -ocular reflex  The neural integrator

11. Fixation Fixation in the primary position involves the visual system's ability to detect drift of a foveating image and signal an appropriate corrective eye movement to refoveate the image of regard. Involved with the oculomotor system

12. Vestibulo -ocular reflex The vestibulo -ocular reflex is a complex system of neural interconnections that maintains foveation of an object during changes in head position The proprioceptors of the vestibular system are the semicircular canals of the inner ear. The semicircular canals respond to changes in angular acceleration due to head rotation

13. Neural integrator When the eye is turned in an extreme position in the orbit, the fascia and ligaments that suspend the eye exert an elastic force to return toward the primary position To overcome this force, a tonic contraction of the extraocular muscles is required. A gaze-holding network called the neural integrator generates the signal. The cerebellum , ascending vestibular pathways , and oculomotor nuclei are important components of the neural integrator

14. Classification Based on Aetiology Based on Onset Based on direction of Movement Based on Pattern of movement Based on Pattern of Manifestation Based on Amplitude Based on Frequency

15. Congenital nystagmus Usually not noted at birth but becomes apparent during first few months of life Congenital Motor Nystagmus Congenital Sensory Nystagmus Periodic alternate Nystagmus Latent Nystagmus ( fusion maldevelopment nystagmus Syndrome) Manifest latent Nystagmus

16. Congenital Motor Nystagmus Horizontal Uniplanar Bilateral Conjugate Head turn to achieve Null Point Improves with convergence Worsen on attempted fixation Reverse response to OKN stimulus ( fast phase in direction of moving OKN drum)

17. Periodic alternating nystagmus (PAN) PAN is a conjugate, horizontal jerk nystagmus with the fast phase beating in one direction for a period of approximately 1-2 minutes. The nystagmus has an intervening neutral phase lasting 10-20 seconds The nystagmus begins to beat in the opposite direction for 1-2 minutes then, the process repeats itself

18. Periodic alternating head turn to minimise nystagmus & oscillopsia Causes: lesions of the cerebellum

19. Spasmus nutans Triad of symptoms: Nystagmus Head nodding Torticollis (head tilt or head turn) Onset usually in the first year of life (3-15 months). Disappears by 3-4 yrs of age

20. The nystagmus typically consists of small-amplitude, high frequency oscillations and usually is bilateral, but it can be monocular, asymmetric, and variable in different positions of gaze Usually benign Neuroimaging recommended ( gliomas may mimic spasmus nutans )

21. Acquired Physiological: End point nystagmus Vestibular (caloric or rotational) nystagmus Optokinetic nystagmus

22. End point nystagmus Jerk nystagmus On looking extreme lateral or upwards Angle of gaze > 45 Degree

23. Vestibular nystagmus Jerk nystagmus Altered inputs from vestibular nuclei to horizontal Gaze Centre(PPRF) Demonstrated by caloric test: normal response Cold water : opposite side Warm water : same side Cold water in both ears: upwards Warm water in both ears : downwards COWS Cold slows things down

24. Optokinetic nystagmus Jerk nystagmus Induced by moving a full visual field stimulus Slow phase (pursuit) : eye follows the target Fast phase ( saccade): eye fixates on next target Uses: Detecting malingering Testing visual potential in children

25. Pathological Nystagmus associated with poor vision (sensory) Anterior segment: cataract, aniridia Retinal diseases: RB, ROP, Intrauterine infections Nystagmus associated with neurological diseases (motor) 1.End gaze paretic nystagmus ( horizontal gaze center) 2.Convergence retraction nystagmus ( vertical gaze, parinaud’s )

26. 3.Vestibular nystagmus : Central ( brainstem nuclei) Peripheral ( labyrinths, VIII CN) 4.Downbeat nystagmus ( cervicomedullary junction) 5.Upbeat nystagmus ( cerebellum, medulla) 6. Seesaw nystagmus ( parasellar lesions) 7. Periodic Alternating Nystagmus

27. Gaze paretic nystagmus Most common type Absent in primary position and is not visually disabling Beats in the direction of gaze Causes: Anticonvulsants Brainstem lesions C erebellar lesions

28. Convergence-retraction nystagmus Not truly a nystagmus Bil adducting saccades causing convergence of both eyes Elicited by having the patient to look up, at which time the eyes converge & retract Causes: Dorsal midbrain lesions

29. Vestibular nystagmus Feature Peripheral Central Disease of vestibular origin Disease of the brainstem Direction Intensity increases when the eyes are turned in direction of fast phase Direction of nystagmus may change with gaze Visual fixation Inhibits nystagmus No inhibition Severity of vertigo Severe Mild Induced by head movements Often Rare Associated eye movement deficit None Pursuit or saccadic defect Other findings Hearing loss CNS involvement

30. Upbeat nystagmus Type of jerk nystagmus with fast phase upward in primary position Often worsens in upgaze Causes: lesions of medulla, cerebellar vermis , midbrain Rx: base up prisms in reading glasses can be used to force the eyes downward

31. Downbeat nystagmus Type of jerk nystagmus with fast phase downward in primary position Often worsens in downgaze Oscillopsia is usually prominent Causes: lesions at cervicomedullary junction Rx: base down prisms in reading glasses can be used to force the eyes upward

32. Seesaw nystagmus Defined as pendular nystagmus with elevation and intorsion of one eye simultaneous with depression and extorsion of other eye Followed by reversal of cycle, so that the eyes move like a seesaw Causes: parasellar lesions, pituitary tumors Produces very disabling oscillopsia that responds poorly to any Rx

33. Nystagmus associated with strabismus Latent /manifest-latent nystagmus Manifest nystagmus Nystagmus blockage syndrome

34. Manifest nystagmus Manifest-latent nystagmus Pendular nystagmus Jerk nystagmus No change on abduction Increased on abduction No change on covering one eye Increase on covering one eye Null zone is present Fast phase always towards fixing eye Less commonly associated with infantile esotropia Always associated with esotropia Binocular visual acuity same as uniocular Binocular visual acuity better than uniocular

35. Nystagmus blockage syndrome Inverse relationship with esotropia Esotropia is a mechanism of blocking the nystagmus The fixing eye is preferred to be in adduction ,face turn is in the direction of fixing eye

36. Type of Nystagmus Localizing value Seesaw Nystagmus Parasellar Tumours , Syringobulbia , Brainstem Stroke Downbeat Nystagmus Leison in the foramen Magnum, Syringobulbia , Lithium and Phenytoin toxicity , Wernicke Encephalopathy, Demyelination,Hydrocephalus Upbeat Nystagmus Posterior Fossa Leisson , drugs, Convergence Retraction Nystagmus Dorsal Midbrain Syndrome Bruns Nystagmus Cerebellopontine Angle tumours

37. Nystagmoid conditions Movements which are not regular and rhythmic: Oculopalatal myoclonus Opsoclonus Ocular bobbing

38. Oculopalatal myoclonus Type of vertical pendular nystagmus Coexisting with tremor of the facial muscles, larynx, palate Present during sleep Cause : usually develops months after an infarction or hge involving mollaret triangle Rx: Gabapentine

39. Ocular bobbing Characterised by conjugate eye movements, beginning with a fast downward movement f/b slow drift back to midline Causes: 1. comatose patients with massive pontine lesion 2.metabolic encephalopathy

40. Superior oblique myokymia Defined as oscillation of one eye due to intermittent firing of the superior oblique muscle Produces oscillopsia or intermittent diplopia elicited by having the patient look in the direction of the superior oblique muscle Characterised by monocular, rapid, intorsional movements

41. Usually benign No underlying etiology is found Neuroimaging : r/o post fossa tumors Refractory cases: surgical weakning of the superior oblique muscle can be performed

42. Treatment Nonsurgical : non neurological causes 1.Optical devices Glasses: overminus lenses stimulate accommodative convergence and thus dampens nystagmus Contact lenses: helpful in high refractive errors by giving good visual stimulus for fusional control

43. Prisms : can be used for 2 purposes 1. To induce fusional convergence by using 7 PD base out prism in front of each eye 2. pre op evaluation in a patient with face turn prisms are inserted with the apex in direction of gaze Useful as a diagnostic trial ,but as a therapeutic alternative are not helpful

44. Occlusion therapy: Trials with conventional occlusion have been found to be effective As amblyopia gets corrected and vision improves, nystagmus finally decreases

45. Pharmacologic Mx These drugs hypothetically inhibit excitatory neurotransmitters within CNS Baclofen : congenital nystagmus , seesaw nystagmus , periodic alternating nystagmus Carbamazepine : widely used for superior oblique myokymia

46. Pharmacologic denervation Botulinum toxin A act by blocking the neuromuscular transmission used in 2 distinct ways to dampen nystagmus 3 units of toxin is injected in each of the 4 horizontal rectus muscles Single large dose of drug into the retrobulbar space Effect last for only few months

47. Surgical Based on 3 principles: To shift the null position if any to the primary position To induce extra convergence innervation by weakening medial recti , to dampen nystagmus To reduce the amplitude of the nystagmus by weakening the muscle force of all recti

48. Thank You