2. OPTIC NERVE:
ANATOMY
• Second Cranial Nerve
• Afferent Fibres though termed tract
are equivalent to white matter of
brain
• Continuation of Axon From
ganglion Cells (Second Order
Neuron)
• Optic Disc To Optic Chaisma
• 50mm in length
3. OPTIC NERVE: COVERING
Meningeal Sheath
Innermost: vascular pia mater
Outermost : Arachnoid mater
Tougher Duramater continuous
with sclera
Subarachnoid Space and sub
dural space is continuous with
brain and contains CSF
4. OPTIC NERVE:
MICROSCOPY
• 1.2 million each of 2-10µm in
diameter
• 600 bundles →2000 fibres, fibrous
septae derived from the pia mater
• unmyelinated axons traverse and
acquire myelin sheaths outside the
globe
• one-third of the fibres = central 5°
of the visual field (:. macular
disease and disease of optic nerve
can mimic)
• No Neurilemma Hence No
Regeneration
• Contains Astrocyte,
Oligodendrocyte and Microglia
5. OPTIC NERVE:
PHYSIOLOGY
Neural Signals: myelinated fibres
Saltatory Conduction Via the cell
membrane
Conduction Velocity(m/s) = 6 x
diameter of fibre
Axoplasmic flow :
Orthograde axoplasmic transport
(from the eye to the brain)
Slow: proteins, enzymes
Intermediate : mitochondria
Rapid : Sub cellular components
Retrograde axoplasmic transport
Intermediate: lysosomes and mitochondria
6. OPTIC NERVE:
BLOOD SUPPLY
Pial Network Of vessels
Central retinal artery : end artery that
enters the optic nerve approximately
1 cm behind the globe
Optic Nerve Head
Surface layer: Capillaries of Retinal
Arterioles
Prelaminar Region: Centripetal Branches
of Peripaplillary Choroid
Lamina Cribrosa: Branches from
Posterior Ciliary artey and arterial Circle
of Zinn
Retrolaminar Part : centrifuagl branches
of central retinal artery and Centripetal
Branches of plial Plexus
7. OPTIC NERVE: PARTS
Intra canalicular
1mm
1.5 mm in vertical
diameter
Starts from optic
disc
Pierces choroid
and sclera in
Lamina cribrosa
Visible in fudus
examination
Intra orbital
25-30 mm
3-4mm in diameter
(Myelin sheath of nerve
fibre)
From globe To Optic
Foramen
Surrounded by Annulus
of Zinn and the origin of
4 recti
S shaped
Partly adherent with
superior rectus sheath
Anteriorly free with
orbital fat
Intra ocular
6mm
Optic canal
Dura fused to
periosteum
Related to
Ophthalmic artery:
inferolaterally
→crosses obliquely
→medially
Sphenoid and
posterior ethmoidal
sinuses medially :
thin lamina
papyraceae
10mm (5-16mm)
Above cavernous
sinus
Converses with
C/L optic nerve
over diaphragm
sellae
Forms Optic
Chaisma
Long segment
Intra cranial
12. Optic disc
Usually unilateral
Children
(1/3 of cases)
Papillitis Neuroretinitis
Optic Nerve head with
cointagious retinal
Inflammation
OPTIC NEURITIS: ANATOMICAL
TYPES
Optic Nerve behind eye
ball
No fundal changes:
lately pale fundus
Most common in adult
(2/3 cases)
Assosciated with MS
Retrobulbar
13. OPTIC NEURITIS : CLINICAL
FEATURES
Asymptomatic
Symptoms :
Pain Mild dull aching ; with ocular
movement
Visual loss: Profound, sudden and
progressive
Visual Obscuration in bright light
Reduced dark adaptation
Impaired color vision
Movement Phosphenes
Uhthoffs Symptom
Pulrich’s Phenomenon
History
Similar previous episode of loss of
vision
Facial or extremity weakness
Positive family history
14. OPTIC NEURITIS : SIGNS
Reduced visual acuity
Afferent pupillary defect: Marcus Gunn Pupil
Dyschromatopsia
Diminished light brightness sensitivity
Diminished contrast sensitivity
Visual field defects:
Classical: Central Scotoma, centrocaecal scotomas,
nerve fibre bundle defect
ONTT : altitudinal, arcuate and nasal field defect
15. OPTIC NEURITIS :
SIGNSOpthalmoscopy
Papillitis :
Hymeremia of disc
Blurred margins
Obliterated physiological cup with
edematous disc
Congested tortous retinal veins
Sphinter hemorrhage
Fine exudates
Neuroretinitis
Plus Macular star formation
Retrobulbar Neuritis
“Neither Ophthalmologist Nor patient sees
anything”
Visually Evoked Response :
17. OPTIC NEURITIS : NATURAL
HISTORY AND PROGNOSIS
Visual acquity and color vision lost progressively over 2-5 days
Recovery (characteristic) : Slower than progression and starts at 2
weeks and over 4-6 weeks
75% of patients recover visual acuity to 6/9 or better 1
Colour vision, contrast sensitivity and light brightness appreciation
often remain abnormal
10% of patients develop chronic optic neuritis 1
1 Kanski
18. RELATION TO MULTIPLE
SCLEROSIS
Most common presenting feature of MS (15–20% )1
75% of female and 35 % of patient ULTIMATELY develop MS 2
Optic neuritis occurs at some point in 50% of patients with established
MS 1
Normal finding MRI 16% develop MS (5 year follow up ) 1
ONTT reported 10 year risk of MS 56% with atleast 1 MR T2 lesion1,2
those with no lesions have a 22% risk 1
The overall 10 year risk of developing MS following an acute episode
of optic neuritis is 38%.
In a patient with optic neuritis, the subsequent risk of MS is increased
with winter onset, HLA-DR2 positivity and Uhthoff phenomenon 1
1 Kanski
2 Medscape
19. OPTIC NEURITIS : INVESTIGATION
Exclude other cause
CSF :myelin basic protein, oligoclonal bands with raised IgG >15%
Neuromyelitis Optica (NMO) IgG specific autoantibody marker
MRI Highly Sensitive and Specific (0.3T)
Gandolium enhancement
ONTT reported 10 year risk of MS 56% with atleast 1 MR T2 lesion
VEP
Abnormal even with normal MRI findings
Mrked prolonged latency period
20. OPTIC NEURITIS : TREATMENT
ONTT :
Strong evidence against ISOLATED USE OF ORAL STERIOD (increased
rate of recurrence)
Intravenous methylprednisolone sodium succinate 1g daily for 3
days followed by oral prednisolone (1 mg/kg daily) for 11 days
and then tapered over 3 days.
No prognostic benefit only hasten the recovery of visual function
21. ONTT
Prospective Study
Randomized clinical trail
448 eligible patient (presenting with U/L vision defect in last 8 days)
Four of the trial's major findings
the prevalence of fellow eye abnormalities
types of visual field defects,
adverse effects of oral corticosteroid treatment,
delay in onset of MS in patients treated with intravenous corticosteroids—were all
unanticipated.
22. OPTIC NEURITIS : TREATMENT
Controversy : Wait and watch without steroid VS IV steroid therapy
Newer approaches
Intramuscular interferon beta-1a (generally used after second attack)
Plasma exchange in acute severe optic neuritis
Erythropoietin
Rituximab for NMOSD
23. REFERENCES
Kansi Bowling Clinical Ophthalmology 7e
Khurana AK- Comprehensive Ophthalmology 5e
Parsons disease of Eye 21e
Medscape
The Optic Neuritis Treatment Trial : A Definitive Answer and Profound
Impact With Unexpected Results, JAMA Ophthalmology, Vol 126, No.
7 http://archopht.jamanetwork.com/article.aspx?articleid=420680
Editor's Notes
whereas true peripheral nerves possess Schwann cells, fibroblasts and macrophages. As with white matter of the brain, the optic nerve has no powers of regeneration
The axons of the optic nerve acquire myelin sheaths proximal to the lamina cribrosa and do not possess a neurilemma. Like other parts of the central nervous system, the optic nerve is covered with pia, arachnoid and dura mater as soon as the nerve leaves the eyeball.
Orthograde axoplasmic transport
(from the eye to the brain) has a slow component
(proteins and enzymes) that progresses at 0.5-3.Omm/
day, an intermediate component (mainly mitochondria)
and a rapid component (subcellular organelles) that
moves at 200-1000 mm/day. Retrograde axoplasmic transport
of lysosomes and mitochondria (from the brain to
the eye) also occurs at an intermediate rate.
The central retinal artery is an end artery that enters the optic nerve approximately 1 cm behind the globe
Retinal capillaries supply the inner two-thirds of the retina, with the outer third being supplied by the choriocapillaris
1 Demyelinating, which is by far the most common cause. 2 Parainfectious, which may follow a viral infection or immunization. 3 Infectious, which may be sinus-related, or associated with cat-scratch fever, syphilis, Lyme disease, cryptococcal meningitis in patients with AIDS and herpes zoster. 4 Non-infectious causes include sarcoidosis and systemic autoimmune diseases such as systemic lupus erythematosus, polyarteritis nodosa and other vasculitides.
myelin is phagocytosed by microglia and macrophages, subsequent to which astrocytes lay down fibrous tissue in plaques
1 Demyelinating, which is by far the most common cause. 2 Parainfectious, which may follow a viral infection or immunization. 3 Infectious, which may be sinus-related, or associated with cat-scratch fever, syphilis, Lyme disease, cryptococcal meningitis in patients with AIDS and herpes zoster. 4 Non-infectious causes include sarcoidosis and systemic autoimmune diseases such as systemic lupus erythematosus, polyarteritis nodosa and other vasculitides.
Uthoffs Symptoms: Tranisent obscuration of vision with exertion or exposure too heat
Pulfrich Phenomenon : Impaired depth perception of moving object ie object moving in a straight line likely to have curved tracejctory
The most common justification for both the phenomenon is assymetrical conduction of nerve impulses
Signs of optic nerve dysfunction
1 Reduced visual acuity for distance and near is common but may also occur with a great variety of other disorders. 2 Afferent pupillary defect (see below). 3 Dyschromatopsia (impairment of colour vision), which mainly affects red and green. A simple way of detecting a uniocular colour vision defect is to ask the patient to compare the colour of a red object. 4 Diminished light brightness sensitivity, often persisting after visual acuity returns to normal, as for instance following an attack of optic neuritis. 5 Diminished contrast sensitivity (see Ch. 14). 6 Visual field defects, which vary with the underlying pathology, include diffuse depression of the central visual field, central scotomas, centrocaecal scotomas, nerve fibre bundle and altitudinal (
The light reflex is mediated by the retinal photoreceptors and subserved by four neurones (Fig. 19.33). 1 First (sensory) connects each retina with both pretectal nuclei in the midbrain at the level of the superior colliculi. Impulses originating from the nasal retina are conducted by fibres which decussate in the chiasm and pass up the opposite optic tract to terminate in the contralateral pretectal nucleus. Impulses originating in the temporal retina are conducted by uncrossed fibres (ipsilateral optic tract) which terminate in the ipsilateral pretectal nucleus. 2 Second (internuncial) connects each pretectal nucleus to both Edinger–Westphal nuclei. Thus a uniocular light stimulus evokes bilateral and symmetrical pupillary constriction. Damage to internuncial neurones is responsible for light-near dissociation in neurosyphilis and pinealomas. 3 Third (pre-ganglionic motor) connects the Edinger–Westphal nucleus to the ciliary ganglion. The parasympathetic fibres pass through the oculomotor nerve, enter its inferior division and reach the ciliary ganglion via the nerve to the inferior oblique muscle. 4 Fourth (post-ganglionic motor) leaves the ciliary ganglion and passes in the short ciliary nerves to innervate the sphincter pupillae. The ciliary ganglion is located within the muscle cone, just behind the globe. It should be noted that, although the ciliary ganglion serves as a conduit for other nerve fibres, only the parasympathetic fibres synapse there.
The findings of the ONTT, reported in more than 50 publications during the past 20 years, have numerous implications. Although the debate continues over the use of intravenous steroids in the management of acute optic neuritis to modify short-term risk of MS in patients with high-risk magnetic resonance imaging (MRI) results, there are other important evidence-based conclusions that make the ONTT legacy indisputable. As a result of the ONTT:
Oral steroids (in standard 1 mg/kg doses) are not used to treat isolated optic neuritis.
The risk of subsequent MS development can now be reliably estimated and MRI is firmly established as the single most important predictor of risk of developing MS.
A low-risk profile (normal MRI results in men with poor vision, severe disc swelling, and no pain) for subsequent MS development was identified.
There is an enormous body of data (vision deficits, MRI findings, spinal fluid analysis, neurologic disability, and vision-related quality of life issues) characterizing the clinical profile of optic neuritis obtained from analysis of carefully characterized and studied patients.
Computerized threshold perimetry and its analysis were rigorously tested and used to characterize optic nerve dysfunction.
Radiologic and laboratory testing of patients with optic neuritis to secure a diagnosis was shown to be unnecessary.
Intravenous corticosteroid treatment was shown to be safe and to be associated with minimal adverse effects in this patient group.
Novel electronic methods of data sharing and remote monitoring of clinical trials were established.
More evidence-based information concerning the relationship of optic neuritis and MS is available for patients and physicians to discuss.
Fellow eye abnormalities and the possibility of simultaneous bilateral or occult demyelinating disease involving the prechiasmatic and retrochiasmatic pathways were confirmed.
Contrast sensitivity and vision testing in general became commonplace and important outcome measures in many MS treatment trials.
Neurologic disability in patients who developed MS after optic neuritis was determined to be mild.
An important subset of patients more apt to have permanent visual impairment with more severe initial vision loss was identified as a target group for future clinical trials, perhaps using neuroprotective drugs, myelin restoring compounds, or both.