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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:


An ophthalmoscope is used to examine the retina and vitreous. Ophthalmoscopy aids visualization of the inside of the back of the eye including the retina, optic disc, choroid and blood vessels. It is often part of a routine eye examination. A direct ophthalmoscope is used for viewing the central retina. It is hand-held and powered with a light source. The instrument has to be adjusted constantly to focus on different structures within the eye. The light can be intense and disturbing. An indirect ophthalmoscope aids in examining the entire retina. This instrument is attached to the doctor's head and allows a clear view of the retina with a special lens. The patient may feel uncomfortable due to the intense light and pressure from the instrument.

Ophthalmoscopy is useful in detecting any changes in the retina due to diseases such as eye disease, diabetes, arteriosclerosis, high blood pressure or macular degeneration. Cataracts and other eye problems can be detected with an ophthalmoscope.

The patient's eyes are dilated so as to allow a good view of the insides of the eye. Some patients develop allergic reaction, vomiting, nausea and dizziness. This test is conducted in a darkened room where the patient is asked to look ahead at a distant spot. The eyes must be held steady without blinking. The ophthalmoscopy procedure may take just about 5 - 10 minutes.

Central Retinal Artery Occlusion

Central retinal artery occlusion (CRAO) is a medical condition that is characterized by loss of vision on account of the blockage of the central artery of the retina. A clot from the carotid artery or the heart is usually the cause for the sudden flow of blood to the retina. Patients suffering from hypertension or carotid artery disease or diabetes are likely to suffer this condition. Arteriosclerosis is another likely cause for Central retinal artery occlusion. Due to the blockage of the retinal central artery, there is sudden and painless loss of vision. Another less severe condition is when a smaller branch artery to the retina gets blocked. This leads to loss in vision that is not as severe as in the case of CRAO.

If not attended to immediately, central retinal artery occlusion can leave a person permanently blinded. It is essential to restore retinal blood flow. An ophthalmologist may try to reduce the pressure in the eye with glaucoma agents. The embolus is moved from the central retinal artery to a branch artery. A surgical procedure whereby a small amount of fluid is drawn from the eye is carried out sometimes. This can seek to lower the pressure in the eye. Laser treatment is also done to reduce swelling and improve vision in the case of branch vein occlusion. But in most cases, it is not easy to restore normal vision.

Tags: #Electroretinography #Ophthalmoscope #Central Retinal Artery Occlusion
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Collection of Pages - Last revised Date: April 17, 2024