This document summarizes different types of nystagmus including physiological nystagmus, pathological nystagmus, pendular nystagmus, jerk nystagmus, latent nystagmus, acquired nystagmus, and discusses grading systems, congenital nystagmus, low vision nystagmus, nystagmus with relatively normal vision, bilateral nystagmus, spasmus nutans, see-saw nystagmus, supranuclear gaze control, gaze palsies, Parinaud's syndrome, internuclear ophthalmoplegia, and paralytic pontine exotropia.

1. Nystagmus a rhythmic oscillation of the eyes. It has many different patterns, and may be physiological or pathological

2. Physiological Nystagmus not due to a disease process Has no benefit, except as a diagnostic tool End point nystagmus Postrotational nystagmus Induced caloric testing Optokinetic nystagmus Voluntary nystagmus

3. Pathological nystagmus

4. Classification When describing the nature of nystagmus, the following terms should be used: Congenital/acquired Jerk/Pendular Direction of fast phase Frequency Amplitude Grading system for gaze

5. Pendular Nystagmus : Usually congenital, or onset in early childhood, due to low vision Both phases have similar speed.

6. Jerk Nystagmus: can be congenital or acquired. Vision is reduced by varying degree (unpredictable), but is the result rather than the cause of the nystagmus Wave form: slow movement (pursuit) in one direction (the defect) fast movement (saccade) in other direction (the correction).

7. Grading System: eg for right beating nystagmus Grade 1 = present in right gaze only Grade 2 = present in right gaze and primary position Grade 3 = present even in left gaze

8. CONGENITAL NYSTAGMUS due to a congenital anomaly of the motor system or to a congenital disorder of vision. may appear during early childhood but is rarely present at birth.

9. Low Vision Nystagmus (syn. Pendular nystagmus) Characterised by slow pendular oscillations generally the wave form is very variable. Established pendular nystagmus (by about 6 months in congenital visual deprivation) has a poor visual prognosis. Rarely ever better than 6/36. Causes: Failure of the fixation reflexes during the critical period (first 3 months) due to eg bilateral corneal scarring, infantile glaucoma, dense cataracts, ocular albinism, optic nerve hypoplasia, optic atrophy, macular hypoplasia, rod monochromatism, Leber’s amourosis.

10. Nystagmus with relatively normal vision Congenital idiopathic jerk nystagmus all types of manifest nystagmus without a primary visual defect, either present at birth or developing during the first few weeks of life as the visual fixation reflexes develop

11. Bilateral nystagmus Eyes otherwise healthy Predominantly in one plane, usually horizontal May start as pendular, but becomes jerky with fast phase to right on right gaze and left on left gaze. Null zone somewhere in between, where acuity usually quite good. Vision often improves on convergence Intensity of the nystagmus increases on attempting fixation

12. May have a superimposed latent component Reduced lid closure Oscillopsia is rare Often face turn, voluntary convergence or head shaking or nodding to minimise nystagmus Commonly hereditary (irregular X-linked dominant) Precise mechanism unknown

13. Management : treatment rarely required, unless an extreme AHP is adopted to achieve maximum VA, when prisms or surgery to centralise the null point can be tried. Occasionally base-out prism to induce convergence

14. Latent and Manifest Latent Nystagmus Horizontal jerk nystagmus presents when the light stimulus is reduced to either eye (eg by occluding). In latent, no observable movement is present on uncovering and full BSV is restored. In manifest latent nystagmus the nystagmus has a reduced amplitude but remains when both eyes are open.

15. ACQUIRED NYSTAGMUS Occurs in many CNS disorders, especially those involving the cerebellum, brainstem and vestibular mechanism. More common in adults labyrithitis, central vestibular disease/tumour, cerebellar damage gaze evoked nystagmus convergence retraction nystagmus (Parinaud,s syndrome) INO

16. Nystagmus The presence of nystagmus should be treated as a sign, rather than a diagnosis and there is great variation and variability in its appearance However there are characteristics of the different types which can aid diagnosis, whilst not being conclusive eg direction, speed and persistence. Nystagmus may be the first sign of a serious neurological defect, and this should always be considered.

17. Two acquired conditions occurring in childhood are as follows: Spasmus Nutans See-Saw nystagmus

18. Spasmus Nutans Nystagmus, involuntary head movements, AHP Onset 3-18 months of age Fine rapid eye movements; jerky, small amplitude, high frequency Horizontal, vertical or rotary, or a combination of these Considerable variation in nystagmus in different positions of gaze Involuntary head movements comprising nodding or shaking, or a combination of both; variable.

19. Spasmus Nutans These do not appear to compensate for eye movement as they are of different frequency Most cases resolve spontaneously by age 3 years. Benign, but can be associated with CNS disease, therefore should be investigated.

20. See-Saw nystagmus Usually an acquired motility disorder associated with chiasmal lesions where one eye elevates and intorts followed by depression and extorsion of the other eye Rare

21. Clinical procedure for nystagmus cases Close questioning as to the onset of the nystagmus, family history, general health, medication, history of CNS disorders, associated symptoms (oscillopsia, vertigo, unsteadiness and loss of vision all imply acquired forms) Carefully note the type of nystagmus, distance/near, latency, AHP etc VA recorded uni- and binocularly, with and without AHP, dist and near and compared Full ophthalmoscopic, slit-lamp (transillumination), and binocular vision assessment

22. Unless 100% sure the nystagmus is congenital or longstanding, refer for further investigation. Neurological causes are rare, but serious and diagnosis of congenital nystagmus should only be made by exclusion of other causes. electro-diagnosis is very valuable as Lebers amaurosis or rod monochromatism cannot be detected ophthalmoscopically.

23. SUPRANUCLEAR GAZE CONTROL Signals which control ocular movement are initiated in the cerebral hemispheres. They are then transmitted to the gaze centres and oculomotor nuclei in the midbrain and pons, and leave the brain in the 3 rd , 4 th and 6 th cranial nerves Supranuclear neuronal pathways: conduct impulses from cerebral hemispheres to gaze centres Internuclear pathways: conduct impulses from gaze centres to ocular motor nucleii Infranuclear pathways: 3 rd , 4 th and 6 th cranial nerves There are three forms of conjugate eye movement (ie as a yoked pair), and each has a different control centre.

24. Saccades =contralateral frontal pre-motor area Pursuit= ipsilateral occipito-parietal area Vestibular reflexes= vestibular nuclei in the pons Conjugate eye movement Control centre

25. These impulses are transmitted to the gaze centres, which mediate the conjugate eye movement. Horizontal and vertical gaze control are quite separate, and therefore should be investigated separately. The horizontal gaze centre is in the pons at the level of the 6 th nerve nucleus. Horizontal movement to the left is controlled by the left horizontal gaze centre, and vice-versa for the right. The vertical gaze centre is in the midbrain but not much is known about vertical gaze control.

26. Gaze Palsies An inability to make a conjugate ocular movement in one direction. This does not cause diplopia since the visual axes remain parallel. By investigating each reflex and conjugate movement in turn, it is possible to establish where a lesion exists

27. GAZE PALSIES Examples supranuclear lesions do not affect vestibular reflexes, so these remain intact (test by calorics or dolls head reflex) frontal lesions cause unilateral saccadic palsies occipital lesions cause unilateral pursuit palsies pontine lesions affect horizontal gaze but not vertical upper midbrain lesions affect vertical gaze Horizontal saccadic gaze palsies are most common

28. Parinauds Syndrome Vertical gaze palsies usually form part of a triad of signs, which is known as Parinauds syndrome. This is relatively rare and is caused by lesions in the upper midbrain. The signs are vertical gaze palsy (saccadic upgaze affected first loss of light reflex (near reflex intact) convergence retraction nystagmus

29. Parinauds Syndrome The convergence retraction nystagmus is seen spontaneously or (more usually) on attempted upgaze. The lesion is thought to cause disinhibition of the ocular motor nuclei allowing bursts of co-firing of the extra-ocular muscles. As the MR is the most powerful muscle this results in convergence and a retraction of the globe Causes: Tumours of the pineal gland *(most common) Atherosclerosis Embolism, Vasculitis

30. Internuclear Ophthalmoplegia Caused by lesions in the medial longitudinal fasciculus (MLF), the area carrying internuclear neurones between 6 th and 3 rd nerves. Type depends on the precise location of the lesion in MLF. It can be unilateral or bilateral: Unilateral: interneurones from one 6 th nerve nucleus affected, causing loss of adduction of the affected MR on attempted conjugate gaze. Saccadic, pursuit and vestibular systems are all affected. Also get abducting nystagmus of the other eye (reason for this is not clear) Convergence can remain intact

31. Internuclear Ophthalmoplegia Bilateral:interneurones from both 6 th nerve nuclei affected. Often assymetric. Patients rarely complain of diplopia Cause; MS is the commonest cause of unilateral (&often bilateral) INO in the younger patient (may be the presenting feature) In the older patient, small blood vessel occlusion is likely in unilateral INO, and tumour is a possibility in bilateral Most spontaneously recover, except if tumour.

32. Paralytic Pontine Exotropia (The “One and a half” syndrome) Lesion affecting both the horizontal gaze centre and the adjacent MLF = gaze palsy + INO. The only remaining horizontal movement is abduction of the unaffected LR with abducting nystagmus ie gaze palsy to one side, INO to the other. Complete “one and a half” syndromes are uncommon, but partial is more common. Cause : tumour is likely.

33. Pseudostrabismus Epicanthus in infants can be more or less pronounced. Epicanthus can obscure the inner canthus giving rise to the appearance of esotropia when none is present. In time epicanthal fold usually disappears with the development of the bridge of the nose Other examples of pseudostrabismus include facial asymmetry failure of the optical (centres of the cornea and lens) and visual axis (fovea to fixation point) to coincide