Electroretinography

Electroretinography or ERG is an eye test used to detect the abnormal function of the retina. The rods, cones and the ganglion cells of the eyes are examined during this test. An electrode is placed on the cornea to measure the electrical response to the light in the retina and the back of the eye. This test helps identify any defects in the retina and can help in identifying if retinal surgery is required.

ERG Procedure

Patient's eyes are dilated and anesthetic drops are placed on the eyes. Eyes are kept open using a speculum and an electrode is placed in the eye. Another electrode is placed on the skin. The patient is made to watch a standardized light stimulus or flash ERG. The signal received is measured according to its amplitude. The readings are taken when the room is normally lit and when the room is dark. If the tests are normal, it will display a normal A and B pattern for each flash.

Abnormal results can indicate:

• Congenital night blindness
  
• Cone Rod Dystrophy (CRD)
  
• Retinal detachment
  
• Vitamin A deficiency
  
• Trauma
  

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.