The term Amaurosis is taken from Greek meaning dark or obscure. It is loss of vision or weakness that occurs without any apparent lesion affecting the eye. Amaurosis is often a short lived episode of blindness in one eye and is referred to as 'fleeting blindness'. An episode of amaurosis if often frightening. Although the visual loss gradually resolves, it is advised to seek medical attention immediately as this may be one of the warning signs of a stroke. Amaurosis is caused due to blood clot or a small piece of cholesterol that breaks off from a large artery and travels upward to the brain or eye. This gets lodged in the main artery supplying blood to the eye. Amaurosis is also caused by blood clots from heart valves or the heart itself due to underlying heart disease.
There are various types of amaurosis. The Leber's congenital amaurosis is inherited. This results in optic atrophy and results in severe vision loss. Amaurosis fugax is a temporary loss of vision in one eye. This is caused by decreased blood flow to the retina. While the majority experiencing amaurosis have a complete symptom abeyance within a few minutes, there is a minority who experience a stroke or a vision loss as a result of amaurosis.
Diabetes, hypertension and smoking tend to aggravate this condition. Sometimes, surgical repair of the mitral valve may result in amaurosis. Deficiency of Vitamin B1 due to Thiamine related cerebrocortical necrosis can also result in amaurosis. Treatment of amaurosis depends mainly upon identifying the source of blood clots and cholesterol that have caused this block in the artery. An ultrasound of the carotid arteries of the neck, a study of the electrical system of the heart and a magnetic resonance angiography scan of the head and neck, an echocardiogram of the heart are often included to reveal the source of the problem and decide on the treatment options.
Leber Congenital Amaurosis
Leber Congenital Amaurosis or LCA is an inherited retinal degenerative disease that causes severe loss of vision in infants. Retina is located at the back of the eye. It contains photoreceptors called rods and cones, through which retina captures light. It converts the light into chemical signals that go to the brain via the optic nerve to interpret it as an image. In case of Leber Congenital Amaurosis, rods and cones do not develop properly and thereby retina ceases to function effectively causing visual impairment. Though LCA can cause complete blindness, most often, infants are born with residual vision.
LCA is a genetic condition that is transmitted by autosomal recessive pattern in which both the parents carry a defective gene to result in LCA. Infants with LCA usually develop other eye related problems such as roving eye movements known as nystagmus, extreme farsightedness hyperopia, deep-set eyes, and sensitivity to bright light. Leber Congenital Amaurosis is a rare disease and only 3 in every 1,00,000 newborns are said to be affected by this condition.
There are 14 types of genes that are associated with Leber Congenital Amaurosis and mutations in any of these genes hinder the development and effective function of the retina. However mutations in the genes naming CEP290, CRB1, GUCY2D, and RPE65 are the most common causes of the LCA.
Symptoms and diagnosis
Infants with LCA may have roving and sunken eyes, cone-shaped corneas termed as Keratoconus and also exhibit oculo-digital reflex in which they press or poke their eyes regularly. Most infants also have sluggish pupils and hyperopia. Rarely, infants with LCA may also have problems with central nervous system and hearing impairment. They may experience seizure disorders, motor impairments and developmental delays.
With LCA, initially, the eyes of the infant may look normal. The diagnosis process is generally initiated after few weeks of the birth, when the infant fails to respond to the visual stimuli. The LCA cannot be easily diagnosed based on the symptoms alone as many other eye diseases also present with similar warning signs. Electroretinography (ERG) test is usually advised to evaluate the retinal function and diagnose LCA. If ERG results confirm poor retinal function, genetic testing will be performed to confirm Leber Congenital Amaurosis.
Treatment of Leber Congenital Amaurosis
No effective treatment is currently available for Leber Congenital Amaurosis. Palliative and supportive care is normally provided to the patients based on symptoms. Those with slight remaining vision are given low-vision aids, including electronic, computer-based and optical aids.
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Bibliography / Reference
Collection of Pages - Last revised Date: December 2, 2020