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Cortical Blindness

Cortical blindness is a condition which involves complete vision loss caused by damage to the occipital lobe of the brain.


Presentation

Cortical blindness encompasses loss of vision, which is generally severe but may be of various degrees in some occasions. Distinct types of the condition are Riddoch syndrome and Anton-Babinski syndrome. Patients who suffer from the Riddoch syndrome experience a loss of vision related to static objects, while they can see anything that is moving. Moving objects may lack color or significant detail. The Anton-Babinski syndrome involves total loss of vision, accompanied by the patient's unawareness that they can no longer see. Patients are unable to discern objects, walk or orientate, but remain convinced that their ability to see has not been damaged. They insist that they are being lied to, but they usually become suspicious when they collide with objects or fall into walls. Hallucinations are also a frequent observation in patients with cortical blindness.

Hypoventilation
  • Hypoventilation due to narcotics with subsequent hypercarbia and blood-brain barrier breaching may be implicated in the pathogenesis of this complication. Copyright (c) 2006 Wiley-Liss, Inc.[ncbi.nlm.nih.gov]
  • […] multisystems atrophy characterized by preferential degeneration of the cerebellum and brainstem producing symmetric parkinsonism and ataxia , dysarthria , dysphagia , pyramidal signs, and often ocular motility disorders Ondine's curse (central alveolar hypoventilation[strokecenter.org]
Hematochezia
  • CASE: A 3-year-old female child was brought with the complaint of diffuse abdominal pain and hematochezia, which was preceded by high grade fever and cough.[ncbi.nlm.nih.gov]
Melena
  • Three days later she developed hematuria, hematemesis, melena and hemoptysis along with palpable purpura. Four days later she became irritable and developed a few episodes of generalized tonic clonic seizure, followed by cortical blindness.[ncbi.nlm.nih.gov]
Palpable Purpura
  • Three days later she developed hematuria, hematemesis, melena and hemoptysis along with palpable purpura. Four days later she became irritable and developed a few episodes of generalized tonic clonic seizure, followed by cortical blindness.[ncbi.nlm.nih.gov]
Frontal Headache
  • A 66-year-old white man presented at the emergency room complaining of severe frontal headache, disorientation, and progressive blurred vision. The initial physical examination disclosed a blood pressure of 200/176 mmHg.[ncbi.nlm.nih.gov]
Scanning Speech
  • speech (ataxic dysarthria ) abnormal staccato-like speech due to a lesion of the cerebellum or cerebellar pathways scaphocephaly (dolichocephaly) premature closure of the sagittal suture schizencephaly developmental birth defect characterized by abnormal[strokecenter.org]

Workup

The first step to diagnose cortical blindness is to establish that vision loss is not a result of eye dysfunction. A person with healthy eyes is expected to have a normal pupil reflex. Asking the patient to describe an object found in the room's surroundings will reveal their inability to describe it or distinguish vital characteristics such as shapes and dimension. The presence of visual hallucinations can further point to the direction of a neurologically-induced case of blindness rather than an ocular one.

Fundoscopy is expected to be normal in patients with cortical blindness. A computerized tomography scan may reveal irregularities on the occipital lobe, depending on the cause of the condition.

Another useful diagnostic tool is the electroencephalogram (EEG). Patients with cortical blindness exhibit slow focal waves, a 10-Hz rhythm irrespective of eye opening and closing, as well as a total absence of alpha rhythm.

The Anton-Babinski syndrome is diagnosed upon clinical examination, when the patient displays inability to discern objects or people around them, but at the same time insists that their vision is intact. Riddoch syndrome is also diagnosed with the clinical examination, since the patient will be able to see a moving finger, hand or person, but will be unable to describe an object that is not in motion.

Epileptiform Activity
  • Interestingly, this patient also presented posterior rhythmic epileptiform activities on electroencephalogram during the first 36 h.[ncbi.nlm.nih.gov]
  • activity; associated with infantile spasms ice cream headache nickname given to headaches that are cold induced; common in migraine ice-pick headache indomethacin-responsive headache disorder characterized by momentary, sharp, and/or jabbing pain that[strokecenter.org]
Right Bundle Branch Block
  • Cardiologic investigations revealed right bundle-branch-block, left ventricular wall thickening and LVHT in the left ventricular apex and the lateral wall.[ncbi.nlm.nih.gov]

Treatment

Cortical blindness can be caused by many underlying diseases. In some cases it may regress, but in some others the damage is permanent. There is not specific way to treat the condition and every treatment plan should be drawn based on the underlying condition. Neurologists perform therapeutic plans aiming at rehabilitation: contrasting colors and discernible patterns are used to train the eye in order to achieve some degree of visual sense. Patients are advised to live in a house where objects are maintained in the same positions and not moved around; it is believed that seeing the same object continually and being aware of what is and looks like will eventually help the brain re-recognize it visually as well.

Prognosis

Cortical blindness that is not caused by a surgical procedure or a vascular event has a generally favorable prognosis. Young age, absence of comorbidities and cognitive defects constitute good prognostic factors in every age.

Incidents of cortical blindness caused by strokes or other types of embolization are viewed in a more negative light, prognostically speaking; so are patients who exhibit bi-occipital anomalies in a computerized tomography scan. Hypertension, diabetes and speech impairment are signs that indicate a potentially worse outcome. Congenital cortical blindness is up to this point medically irreversible.

Etiology

Cortical blindness may be congenital or acquired and is a result of many underlying conditions that damage the occipital lobe of the brain through various mechanisms. The most common cause of the disease is an arterial occlusion of the one or both of the posterior cerebral arteries [1]. Cortical blindness can, depending on the cause and severity, be permanent or transient. Conditions that may lead to acquired cortical blindness include:

  • Traumatization of the head in the region of the occipital lobe.
  • Creutzfeldt-Jakob disease and dementia
  • Encephalitis
  • Lesions of the primary visual cortex
  • Anticonvulsants administered for the treatment of epilepsy
  • Eclampsia [2] and pre-eclampsia [3] [4]
  • Administration of contrast agent during angioscopy [5]

A distinct type of cortical blindness is the Riddoch syndrome. It is caused by lesions that are located in the visual cortex and, instead of leading to total blindness, cause inability to see static things. Moving things can be seen by patients but usually without color or extreme detail.

On the other hand, congenital cortical blindness may be a result of congenital structural defects of the occipital lobe or traumatization, perinatal ischemia and stroke and CNS inflammation.

Epidemiology

Temporary cortical blindness has been observed after the performance of procedures such as an angiography, aortography and myelography [6]. Data have showed that the incidence of the condition post cerebral angiography was approximately 1% [7], whereas a vertebral angiography in associated with higher risk of developing temporary cortical blindness [8].

Sex distribution
Age distribution

Pathophysiology

The pathophysiological mechanism leading to an incident of cortical blindness absolutely depends on the underlying cause. Surgical procedures performed on the heart are an important cause, since arterial clamping may disrupt blood flow to the brain and, in particular, the occipital lobe [9], a cerebral hemorrhagic event may occur [10] and embolism is also a possibility; the latter includes clots, as well as fat and air emboli [11]. The calcarine cortex may also be subject to substantial hypoperfusion, leading to death during the operation [12].

In cases of angiography-induced cortical blindness, it is believed that the contrast material may cause significant hypotension and blood flow reduction to the brain, vasospasm or disrupt the blood-brain barrier [13].

Prevention

Cortical blindness cannot be prevented, as it is a complication of a plethora of other diseases. However, people who suffer from conditions likely to lead to cortical blindness, such as coagulopathies and atherosclerosis, are advised to adhere to their doctor's advice and recommendations in order to better control them.

Summary

Vision comprehensively requires two major structures in order to be normal: the eyes and the occipital lobe of the brain. Blindness or any type of vision distortion can be a result of damage, either to the eye or to the brain. Cortical blindness and cortical visual impairment (CVI) are distinguished from each other based on the degree of the resulting disability: cortical blindness involves complete vision loss, whereas CVI implies a partial vision loss. Both conditions are categorized under "neurological visual impairment" which suggests that vision problems originate from the occipital lobe of the brain, in contradistinction to ocular visual impairment, where the damage lies in the eye itself.
Cortical blindness can be congenital, due to perinatal ischemia and subsequent stroke, meningitis or encephalitis, or it can be acquired [1]. Acquired cortical blindness is also a result of brain ischemia (stroke or heart surgery). The condition may result in permanent or temporary vision loss. An interesting phenomenon is the Anton-Babinski syndrome, which involves the total unawareness by the patients that they have lost their vision, despite any evidence that proves otherwise.

Patient Information

Cortical blindness (CB) is the loss of vision caused by damage to the brain, rather than the eyes themselves. A person may be born with cortical blindness; that is the congenital disease type. Other people may develop CB during the course of their lives and suffer from what is called the acquired disease type.

A child may be born with CB as a result of decreased blood flow to the brain during childbirth, head traumatization prior to birth and inflammation of the brain. On the other hand, people who develop the condition later in life, do so as a result of various conditions that damage the occipital brain lobe: the part of the brain that lies in the back of the skull and is responsible for interpreting visual information collected by the eyes. Strokes, decreased blood flow to the occipital lobe during heart surgery, encephalitis, and angiographic contrast material can all lead to cortical blindness.

Cortical blindness has distinct differences from blindness induced by eye problems. The eyes keep their pupil's reflex: when a ray of light is directed to the pupil, it will become smaller. This simple test greatly helps to discern a case of brain-induced blindness from one caused by ocular problems. A doctor will first examine the eyes of a patient to check for the pupil reflex and will then ask the patient to describe various objects or people that can be found in the room. A person with cortical blindness may be completely unable to describe them, or may be unable to discern dimensions and shapes.

CB is diagnosed with the clinical examination, with a brain CT that may reveal abnormal findings and an EEG, that can also help to corroborate the suspicion of blindness due to brain damage.

The condition may be temporary or permanent, always depending on the underlying disease. Although there is no particular way to treat this condition, visual exercises with contrasting shapes and patterns are recommended, in order to stimulate and re-train the brain to interpret visual information.

References

Article

  1. Aldrich MS, Alessi AG, Beck RW, Gilman S. Cortical blindness: etiology, diagnosis, and prognosis. Ann Neurol. 1987 Feb;21(2):149-58.
  2. Cipolla MJ. Cerebrovascular function in pregnancy and eclampsia. Hypertension. 2007 Jul;50(1):14-24.
  3. Cunningham FG, Fernandez CO, Hernandez C. Blindness associated with preeclampsia and eclampsia. Am J Obstet Gynecol. 1995 Apr;172(4 Pt 1):1291-8.
  4. Do DV, Rismondo V, Nguyen QD. Reversible cortical blindness in preeclampsia. Am J Ophthalmol. 2002 Dec;134(6):916-8.
  5. Demirtas M, Birand A, Usal A. Transient cortical blindness after second coronary angiography: is immunological mechanism possible? Cathet Cardiovasc Diagn 1994;31:161.
  6. Sticherling C, Berkefeld J, Auch-Schwelk W, Lanfermann H. Transient bilateral cortical blindness after coronary angiography. Lancet 1998;351:570.
  7. Horwitz NH, Wener L. Temporary cortical blindness following angiography. J Neurosurg 1974;40:583–586.
  8. Junck L, Marshall WH. Neurotoxicity of radiological contrast agents. Ann Neurol 1983;13:469–484.
  9. Brierly JB. Neuropathological findings in patients dying after open-heart surgery. Thorax 18:291-304, 1963.
  10. Aguilar MJ, Gerbode F, Hill JD. Neuropathologic complications of cardiac surgery. J Thorac Cardiovasc Surg. 1971 May;61(5):676-85.
  11. Gilman S. Cerebral disorders after open-heart operations. N Engl J Med. 1965 Mar 11;272:489-98.
  12. Celesia GG, Archer CR, Kuroiwa Y, Goldfader PR. Visual function of the extrageniculo-calcarine system in man: relationship to cortical blindness. Arch Neurol. 1980 Nov;37(11):704-6.
  13. Horwicz NH, Wener L. Temporary cortical blindness following angiography. J Neurosurg. 1974 May;40(5):583-6.

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Last updated: 2018-06-22 05:14