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Optic Neuropathy
0Disorders of optic nerve involving
degeneration of the nerve.
0
Causes:1. Hereditary
2. Acquired: a) Ischemic
b) Nutritional
c) Toxic (DRUG INDUCED)
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Mechanisms of DION
0Mitochondrial dysfunction
0Disruption of blood flow to the optic nerve
0 Imbalance in ionic photoreceptor metabolism
0Unknown mechanisms
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Drugs Causing Optic Neuropathy
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Drugs Causing Optic Neuropathy
0Most supporting information available for:1. Ethambutol (antitubercular drug)
2. Amiodarone (antiarrthymic drug)
3. Sildenafil (PDE-5 inhibitor)4. Topiramate (anticonvulsant drug)
5. Linezolid (anti-MRSA antibiotic)
6. Vigabatrin (antiepileptic drug)7. Isoniazid (antitubercular drug)
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ETHAMBUTOL
0 First line agent in the treatment of Tuberculosis
0 Its toxicity is dose and duration dependent
0 Dose > 25mg/kg/day
0 Duration > generally 3-6months
0
Earlier toxicity at a lower dose in renal disease
0 Mechanism: Chelation of Copper in retinal cells.
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Ocular Side Effects
0Optic Neuritis with abrupt visual impairment
0Dyschromatopsia (colour vision
abnormalities) with patient c/o fading of
some colours in vision:
1. Red-green or
2. Blue-yellow dyschromatopsia
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Ocular Side effects(contd.)
0Visual field Defects:1. Central type:
a) Decreased Visual Acuity
b) Central or centrocaecal scotomas
c) blue-green colour dyschromatopsia
2. Peripheral type:
a) Peripheral Visual Field constriction
b) Red-green dyschromatopsia
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Treatment and Follow-Up
0 Prompt ophthalmic evaluation (disc may be normal or
slightly swollen with splinter shaped hemorrhages)
0 Immediate discontinuation of the drug
0 Follow-up every 4 weeks for doses > 15mg/kg/day
0 Prognosis: is good with early cessation of treatment
but recovery may take up to 12 months
0 Few patients do develop permanent visual
impairment due to optic atrophy
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AMIODARONE
0 Class III antiarrthymic drug used for ventricular
arrrhythmias
0 Causes reversible Vortex keratopathy in cornea,
conjuctival effects and optic neuropathy
0 Not dose related optic neuropathy
0 Slow onset over years
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Ocular Side Effects
0 Insiduous unilateral or bilateral visual impairment
0 Bilateral disc swelling which may persist for months
after cessation of therapy
0 Visual field defects usually peripheral constriction
(unlike Ethambutol which causes usually central
scotomas)
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D/D
Optic Neuropathycaused by
Amiodarone
Non ArteriticIschemic Optic
Neuropathy
0 Slow onset
0 Mild visual loss
0 Prolonged disc
edema
0 Usually bilateral
0 Slow resolution
0 Relatively quick
onset
0 More visual loss
0 Shortened disc
edema
0 Usually unilateral
0 Rapid resolution
VS
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Treatment and Follow-Up
0Cesssation of drug
0Prognosis: variable and slow
0 Screening: Baseline at the start of start of
treatment and every 6 months but not very
helpful
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VIGABATRIN
0 Second line antiepileptic drug for
uncontrolled partial seizures and infantile
spasms
0 Idiosyncratic toxicity and not dose related
0Presentation of symptoms over months oryears
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Ocular Side Effects
0 Bilateral concentric or binasal visual field defect
0 Ophthalmoscopy may show:
0Peripheral atrophy
0Nasal optic disc atrophy
0Arteriolar narrowing
0Abnormal macular reflex
0 Surface wrinkling
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Follow Up
0Baseline visual field examination before
starting treatment
0Reassessment after 6 months for 3 years and
then annually if no abnormality seen
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Sildenafil
0 PDE-5 inhibitor used for erectile dysfunction in males
0 Mechanism: causes inhibition of PDE-6 in rods and
cones leading to visual disturbances
0 Most common cause of drug associated ocular
toxicities in US
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Ocular side efffects
0 Causes Non Arteritic Ischemic Optic Neuropathy by
causing hypotension in peripheral small arteries
supplying optic nerve0 NAION characterized by sudden, painless, unilateral,
partial, sectoral loss of vision
0 Occurs in individuals already on risk with DM, HTN,
IHD, hyperlipidemia, sleep apnea etc.
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Recommendations
0 Avoid using these drugs in patients with small,
crowded discs
0 Basline ophthalmic examination may be done in at
risk patients to rule out small discs
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LINEZOLID
0 Anti-MRSA antibiotic
0 Optic neuropathy with long term use > 5-11 months
0 Causes gradual, painless, bilateral loss of vision
0 Withdrawal of drug aids recovery
0
Baseline and periodic eye evaluations arerecommended
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ISONIAZID
0 First line antitubercular drug
0 Can produce optic neuropathy in patients with concurrent
hepatic or renal disease
0 Causes mild vision loss, scotomas, and dyschromatopsia
0 Since given with ethambutol, it is recommended to stop
ethambutol first and if symptoms do not resolve then stop
isoniazid
0 Treatment: stop the drug, give pyridoxine
0 Periodic eye examinations to see optic disc swelling.
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Updates!
0 ROLE OF OCT IN ETHAMBUTOL OCULAR TOXICITY:
0 In ethambutol toxicity, early changes are not clinically
apparent on fundoscopy.
0 With OCT we can see loss of retinal nerve fibre layer
as a sign of early toxicity of the drug which would not
be apparent on fundoscopy
0 So OCT is an additional way to objectively monitor
patients on ethambutol in addition to VF testing.
Zoumalan CI, Agarwal M, Sadun AA. Optical coherence tomography can measure axonal loss in patients with
ethambutol-induced optic neuropathy. Graefes Arch Clin Exp Ophthalmol. May 2005;243(5):410-6.
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Thank You!