Approach to Visual Defects

Here we will cover the approach to visual loss. This includes loss of visual acuity and visual field defects.

Loss of visual acuity and visual field defects:

Here we will discuss visual loss from a neurological perspective. This may manifest as decreased visual acuity which ranges from difficulty seeing small objects to total blindness. Another manifestation is visual field defects which are dark or absent areas in the patients vision from which no images are formed.
Visual loss can arise due to problems in the eyes or in the nervous system. The function of the eyes is to form images on the retina. Problems in the eyes causing decreased visual acuity or vision loss include refractive errors and disease of the anterior chamber, the lens or the posterior chamber. These are beyond the scope of the current section. From a neurological perspective the areas of interest include the visual system from the beyond the retina. These are the structures along the visual pathway:

  • Optic nerves, optic chiasm, optic tract, lateral geniculate nuclei and the optic radiation to the occipital cortex.
  • Damage or dysfunction of any of these structures causes vision loss either in the form of decreased visual acuity or a visual field defect.
  • The clinical features on examination are very valuable in localizing these lesions. The key clinical features are described below.

 

Optic nerve lesions:

Lesions here cause optic neuropathy, which may lead to optic atrophy in some cases. If the lesion is inflammatory the term optic neuritis is uses. Features of optic nerve lesions are: decreased visual acuity, relative afferent pupillary defect (RAPD, this is where the consensual light reflex is stronger than the direct light reflex), red desaturation (red colors appear grey or dim), pain on eye movement (especially with optic neuritis). More subtle or incomplete lesions cause scotoma (central or paracentral visual field defects). Usually one eye is affected. If both eyes are affected than both optic nerves need to be involved.
See below for causes of optic nerve lesions.

Optic chiasm lesions:

Lesions of the optic chiasm can cause multiple features depending on which part of the optic chiasm is involved. The classic pattern is bi-temporal hemianopsia. This pattern indicates bilateral damage to the medial portions of the optic chiasm, which carries fibers from the nasal portions of both retina. This translates into the patient not being able to see objects that are in the temporal parts of the visual fields i.e. they can’t see objects positioned laterally in the periphery on either side. If the lesion, for example compressive tumor or aneurysm, is compressing the chiasm asymmetrically the clinical features may appear as optic neuropathy ispilaterally and a superior temporal field defect contralaterally. This is called junctional scotoma.

Optic tract lesions:

Optic tract lesions lead to homonymous hemianopsia. The patient will be unable to see objects on the contralateral visual field from both eyes. For example with a right optic tract lesion the patient will have difficulty seeing objects in the left visual field in either eye.

Lateral geniculate nuclei lesions:

Lateral geniculate nucleus lesions lead to homonymous hemianopsia. The patient will be unable to see objects on the contralateral visual field from both eyes. For example with a right optic tract lesion the patient will have difficulty seeing objects in the left visual field in either eye. Note that homonymous hemianopsia due to lateral geniculate lesions are not macular sparing (they involve the central 10-15 degrees of vision)

Optic radiation lesions:

Optic radiation lesions lead to homonymous hemianopsia. The patient will be unable to see objects on the contralateral visual field from both eyes. For example with a right optic tract lesion the patient will have difficulty seeing objects in the left visual field in either eye. The unique feature of the optic radiation is that is fans out in large loops. This makes it very susceptible to damage from cortical lesions and from large subcortical lesions. Also, because there is a superior loop and an inferior (temporal a.k.a Meyer’s) loop, some lesions may affect one loop but spare the other. This leads to quadrantinopsia. Because the way the optic radiation is organized, superior loop lesions cause inferior quadtrantinopsia. Whereas, temporal loop lesions cause superior quadrantinopsia. Also of note, these lesions spare the central vision (macular sparing)

Occipital cortex lesions:

Occipital cortex lesions lead to homonymous hemianopsia. The patient will be unable to see objects on the contralateral visual field from both eyes. For example with a right optic tract lesion the patient will have difficulty seeing objects in the left visual field in either eye. These lesions spare the central vision (macular sparing) as well.
Uncommonly, lesions of the tip of the occipital lobe can produce a homonymous scotoma involving half the center of the visual field on one side.

Other relevant visual field defect patterns:
  • Enlarged blind spot: This occurs with papilloedema, often this accompanies decreased peripheral vision
  • Central scotoma: this occurs with macular disease and with some forms of optic neuropathy
  • Altitudinal scotoma: the visual field defect is in the superior part of both nasal and temporal visual fields of the affected eye that respects the horizontal midline. This occurs with ischemic optic neuropathy more so than with other causes of optic neuritis such as demyelinating disease, and also with branch retinal artery occlusion and with glaucoma.
  • Arcuate scotoma: the visual field defect is in the inferior part of both nasal and temporal visual fields of the affected eye. This occurs with branch retinal artery occlusion, demyelinating neuropathy, drusen at the optic nerve head and other conditions such as glaucoma.
  • Spiral visual field loss: this is a psychogenic pattern

 

Loss of vision a.k.a. visual loss:

Sudden:

  • Painless:
    • Vitreous hemorrhage
    • Retinal detachment
    • Central retinal vein occlusion CRVO
    • Central retinal artery occlusion CRAO
    • Arteritic ischemic optic neuropathy e.g. giant cell arteritis
    • Age related macular degeneration (wet type if subretinal choroidal neovascular membranes bleed)
  • Painful:
    • Acute angle closure glaucoma
    • Optic neuritis
    • Uveitis/choroiditis etc.
    • Trauma
    • Acute hydrops
    • Pituitary apoplexy

Chronic:

  • Cataract
  • Glaucoma
  • Age related macular degeneration (dry > wet, wet may cause sudden visual loss)
  • Central serous chorioretinopathy
  • Diabetic retinopathy
  • Retinitis pigmentosa
  • Epiretinal membrane
  • Melanoma & other tumours

 

Causes of optic neuropathy:

Optic neuritis:

  • Multiple sclerosis
  • Neuromyelitis optica
  • Systemic lupus erythematosus, Sjogren’s syndrome, Wegener grandulomatosis, Behcet’s disease inflammatory bowel disease,
  • Neuro-Sarcoidosis
  • Chronic relapsing inflammatory optic neuropathy

Ischemic optic neuropathy:

Infection:

  • Syphilis
  • Lyme disease
  • Tuberculosis
  • Bartonella henselae (cat-scratch disease)
  • CMV
  • VZV
  • Measles, mumps,
  • Cryptococcus

Paraneoplastic:

Noninflammatory:

  • Genetic:
    • Leber’s hereditary optic neuropathy (LHON)
    • Dominant optic neuropathy (Kjers’ type, OPA1 gene, Chr. 3q), Recessive optic neuropathy (X-linked, OPA2),
  • Tobacco-alcohol amblyopia a.k.a. nutritional optic neuropathy
  • B1, B2, B3, B6, or B12 deficiency
  • Compression by internal carotid artery aneurysm at the siphon i.e. infrasellar aneurysm
  • Drugs and toxins: Ethambutol, Chloraphenicol, amiodarone, methanol,
  • Radiation optic neuropathy
  • Traumatic optic neuropathy
  • Neoplastic:

 

Causes of altitudinal visual field defect (inferior or superior):

Retinal cause:

  • Branch retinal artery occlusion
  • Branch retinal vein occlusion
  • Retinal coloboma

Optic nerve lesions:

  • Ischemic optic neuropathy (arteritic and nonarteritic)
  • Papilledema
  • Optic disc coloboma

 

Causes of floaters:

  • Normal aging
  • Vitreous hemorrhage
  • Posterior vitreous detachment
  • Vitreous degeneration
  • Inflammatory infiltrates e.g. posterior uveitis

 

Causes of branch & central retinal vein occlusion:

  • Thrombophilia
  • Hyperviscosity syndromes
  • Increased ocular pressure
  • Vessel wall inflammation
  • Diabetes
  • Hypertension
  • Glaucoma (only causes central retinal vein occlusion)

 

Causes of branch & central retinal artery occlusion:

 

Causes of vitreous hemorrhage:

  • Posterior vitreous detachement
  • Proliferative diabetic retinopathy
  • Retinal vein occlusion
  • Trauma
  • Sickle cell retinopathy
  • Vasculitis
  • Subarachnoid hemorrhage (but usually subhyaloid, i.e. between vitreous & retina)

 

Causes of optic disc swelling:

  • Papilloedema
  • Accelerated hypertension
  • Optic papillitis
  • Ischemic optic neuropathy e.g. giant cell arteritis
  • Hypercapnia
  • Central retinal vein occlusion
  • Hyperproteinemic disorders e.g. Waldenstroms macroglobulinemia
  • Pseudopapilloedema

 

Causes of optic neuropathy:

Ischemic optic neuropathy:

  • Arteritic:
  • Non-arteritic:
    • Atheroma a.k.a. atherosclerosis
    • Hypertension
    • Diabetes mellitus
    • Migraine
  • Hematologic :
    • Polycythemia rubra vera
    • Shock (hypotension)
    • G6PD
    • Sickle cell trait
  • Low tension glaucoma

Optic nerve compression:

  • Tumour
  • Glaucoma
  • Aneurysms
  • Paget’s disease

Toxic:

  • Medications: Isoniazid, Ethambutol, Chloramphenicol, Digoxin
  • Drugs of abuse: Methanol, tobacco,
  • Heavy metals: Lead

Vitamin deficiencies:

  • B1 deficiency, B12 deficiency

Hereditary:

 

Causes of optic atrophy: (see optic neuropathy)

  • Multiple sclerosis (due to recurrent optic neuritis)
  • Post optic neuritis
  • Optic nerve compression: see optic neuropathy
  • Toxic optic neuritis: see optic neuropathy
  • Vitamin deficiencies: see optic neuropathy
  • Hereditary: see optic neuropathy

 

Causes of a lost red reflex on fundoscopy:

  • Cataract
  • Vitreous hemorrhage
  • Retinal detachment

 

Causes of chorioretinitis:

  • Idiopathic
  • Toxoplasma
  • Toxoplasma secondary to HIV
  • Granulomatous diseases

 

Causes of cortical blindness & Balint syndrome (simultagnosia, optic apraxia, oculomotor apraxia):