Neuro-ophthalmic Disorders

Relative Afferent Pupillary Defect seen in optic nerve lesion and severe retinal disease  lesion of the optic nerve on one side blocks the afferent limb of the pupillary light reflex pupils are equal and of normal size but the pupillary response to light directed to the affected side is reduced sign observed during the swinging-flashlight test  seen as both pupils dilation when light is swung from normal to abnormal eye the affected side will constrict less therefore appearing to dilate

Visual Pathway The optic nerve is formed by the axons arising from the retinal ganglion cell layer.   It passes out of the eye though the lamina cribrosa of the sclera. It is surrounded by dura, arachnoid and pia mater, continuous with that surrounding the brain.  The optic nerves extend from the posterior pole of the eye to cross at the optic chiasm.  The fibers travel as the optic tract - most of them go to the lateral geniculate body in the thalamus (visual)

Another population sends information to the tectum in midbrain (afferent fibers of the pupillary light reflex)  They leave the lateral geniculate body forming the optic radiations to the visual cortex.  Primary visual cortex responsible for processing visual information is located in the occipital lobe. 

Optic Nerve Intraocular Orbital Intracanalicular Intracranial

Intraocular portion of the Optic Nerve Visible on the ophthalmoscopy as the optic disc.  Central retinal vessels enter and leave the eye here. There is a complete absence of photoreceptors and is known as the blind spot.  Normally slightly vertically oval with an average area dimensions of 1.76mm horizontally and and 1.92mm vertically.  Normal color is yellowish-orange. Sharply defined margin and the nasal side is slightly less distinct due to the greater density of nerve fibers.   There is a central depression called optic cup.

Optic cup is the pale center of the disc and is devoid of neuroretinal tissue. It is important to document the size of the cup.  This is specified as the horizontal and vertical cup to disc ratio. Normal cup to disc ratio is 0.3 mm.   Increased cup to disc ratio indicates a decrease in the quantity of healthy neuroretinal tissue and hence, glaucomatous change. 

Disturbances of the Visual Pathway  

Optic Nerve

Swollen Optic Disc Papilloedema Space-occupying lesions of the optic nerve head Optic disc drusen (calcified axonal material) Gliomas Sarcoidosis Leukemia Papillitis Accelerated (malignant hypertension) Ischemic optic neuropathy Central retinal vein occlusion Pseudopapilloedema Myelinated nerve fibers around the nerve head Peripapillary atrophy in myopia

Optic disc drusen

Myelinated nerve fibers around the nerve head

Peripapillary atrophy in myopia

Papilloedema due to raised ICP Optic nerve sheath is continuous with the subarachnoid space of the brain.  As the CSF pressure increases, the pressure is transmitted to the optic nerve. The sheath acts as a tourniquet and leads to a buildup of material at the level of lamina cribrosa.  This results in characteristic swelling of the nerve head.   Papilloedema may be absent in cases of prior optic atrophy most likely secondary to a decrease in the number of physiologically active nerve fibers. 

Causes Idiopathic intracranial hypertension Intracranial tumors (60%) Craniosynostosis Cerebral edema Encephalitis Obstruction of the ventricular system Decreased CSF resorption Increased CSF production Medications - tetracycline, nalidixic acid, steroids

History Associated visual loss is rare Transient visual obscurations Blurred vision Constriction of the visual field Decreased color perception Diplopia (sixth nerve palsy) Headache, worse on waking and made worse by coughing Nausea, retching, vomiting Pulsatile tinnitus History of trauma Medications

Signs Swollen optic disc with blurry margins Dilated and prominent superficial capillaries No spontaneous venous pulsation of the CRV Hemorrhages over and/or adjacent to the disc Paton's lines  Normal color vision No RAPD Visual field testing large blind spot constricted filed in chronic cases Abnormal neurological signs

Investigations CT scan and MRI of the brain with contrast to identify space occupying lesions MR venography to detect venous sinus thrombosis B-scan ultrasonography to rule out disc drusen Fluorescein angiography  Lumbar puncture 

Treatment Treat the underlying disorder Papilloedema will resolve within few weeks once ICP has been normalized Optic atrophy usually remains Neurosurgery is required for space-occupying lesions and hydrocephalus

Idiopathic Intracranial Hypertension Elevated ICP and presence of disc swelling with no evidence of intracranial abnormality and no dilation of the ventricles on the scan Overweight women in the second and third decades Exposure to drugs such as contraceptive pills and tetracyclines Headache, obscurations of vision, sixth nerve palsies No other neurological problems Progressive contraction of the visual field if the nerve remains swollen for weeks

Treatment by reducing the ICP medications (oral acetazolamide) ventriculoperitoneal shunting optic nerve decompression

Optic Neuritis Inflammation or demyelination of the optic nerve Papillitis - optic nerve head is affected Retrobulbar neuritis - nerve is affected more posteriorly with no disc swelling Many are associated with multiple sclerosis  Age 20 - 45, more in females and Caucasian

Causes Multiple sclerosis (50%) Syphilis Lyme disease Herpes zoster Autoimmune disorders (lupus) IBD Drugs (chloramphenicol, ethambutol) Vasculitis Diabetes

History Usually affects one eye Acute loss of vision that progress over a few days and then slowly improve (some are permanent) Varies from a small area of blurring to complete blindness Distorted vision and reduced color vision  Pain on eye movement in retrobulbar neuritis Preceding history of viral illness 40-70% develop other neurological symptoms to suggest MS

Examination Reduced visual acuity Reduced color vision RAPD due to reduced optic nerve conduction Central scotoma on field testing Normal disc in RN, swollen disc in papillitis

Papillitis

MRI scan can identify additional silent plaques of demyelination Diagnosis of MS is essentially clinical Treatment with steroid may speed up visual recovery Immunosuppressive therapy in case of MS Vision slowly recovers over several weeks but not quite as good as before the attack Repeated episodes may lead to optic atrophy and decline in vision Vision may not recover in atypical cases

Ischemic Optic Neuropathy Degenerative vaso-occlusive or vasculitic  disease of the arterioles Compromise posterior ciliary vessels Ischemia of the anterior optic nerve

Types Arteritic ischemic optic neuropathy giant cell arteritis advanced age mostly involving nearly complete vision loss  Non-arteritic ischemic optic neuropathy results from the coincidence of cardiovascular risk factors in a patient with "crowded" optic discs more common younger age group few near total loss of vision cases

Symptoms Sudden loss of vision or visual field, often on waking Vision in that eye is obscured by a dark shadow, often involving just the upper or lower half of vision, usually the area towards the nose  Pain or scalp tenderness (giant cell arteritis) 

Giant Cell Arteritis Autoimmune vasculitis in patients over the age of 60 Affects arteries with an internal elastic lamina Present with any combination of: sudden loss of vision scalp tenderness (e.g. on combing) pain on chewing (jaw claudication) shoulder pain malaise

Signs Reduction in visual acuity Field defect, absence of the lower or upper half of the visual field (altitudinal scotoma) Swollen and hemorrhagic disc, normal retina and retinal vessels Pale disc in arteritic ION Small normal disc with small cup in non-arteritic ION Tender temporal artey in GCA

Investigations Elevated ESR and CRP in GCA (1 in 10 normal) Temporal artery biopsy Color duplex ultrasound -  hypoechoic halo around the temporal artery lumen  Full blood count to exclude anemia Blood pressure Blood sugar

Treatment IV and oral high-dose steroids if GCA is suspected Dose is tapered over the ensuing weeks according to symptoms and the response of ESR and CRP Steroids will not reverse the visual loss but can prevent the involvement of the other eye No treatment for non-arteritic ION other than management of underlying conditions

Prognosis Second eye may rapidly become involved if untreated (GCA) Steroid therapy may have to be continued on a prolonged basis and monitored Significant rate of involvement of the second eye in non-arteritic form (40 - 50%)  Unusual for the vision to get progressively worse in non-arteritic form Vision lost does not recover in both conditions

Optic Chiasm

Causes pituitary tumor symptoms related to hormonal disturbance Meningioma Craniopharyngioma 

Presentation Bitemporal hemianopia Missing objects in the periphery of visual field Difficulty in fusing images, causing the patient to complain of diplopia although eye position and movement are normal Difficulty with tasks requiring stereopsis such as pouring water into a cup or threading a needle

Optic Tract, Radiation & the Visual Cortex

Causes tract - vascular or neoplastic radiation - neoplasia cortex - cerebrovascular accident

Presentation Homonymous hemianopic field defect tract - incongruous radiation or cortex - congruous  Visual loss is of rapid onset; a slower onset suggests a space-occupying lesion