Print View

 Dark Adapted Threshold (DAT)

 Electroretinogram (ERG) - awake

 Electroretinogram (ERG) - under anesthesia

 Sweep Visual Evoked Potential (SVEP)

Dark Adapted Threshold (DAT) Top

Dark adapted threshold (DAT) is a vision test that measures the adjustment of the eye occurring under low levels of illumination. When light enters the eye, it ultimately reaches the rods and cones, which are two types of cells in the retina. Rods handle vision in low light conditions and cones handle color vision and detail. The rods and cones each react differently during the DAT test, and are measured on a graph. The test determines the threshold, or minimum light intensity required to produce a visual sensation in the child's eye. In order to perform this test, the child is asked to sit in the dark for a half hour. This allows the eyes to be most sensitive for the test. Once the eyes have fully adapted, the child stands in front of a black projection screen. Dim spots of light are projected onto the screen, one at a time, on either the right or the left side. The spots get dimmer as the test goes on. The child is asked to point to the spots until he or she can no longer distinguish them. In order to keep the child's attention on the screen, sometimes the doctor will wave a brighter light on the screen to hold the child's interest when the test becomes harder to see. When an infant is being tested, an observer with a night vision camera records the head and eye movements of the child as they look at the spots. Once the patient can no longer see the spots, the dark adapted threshold is determined. The DAT test lasts for about 10 to 15 minutes.

We are happy to discuss the reports with you and your child's other physicians. When you are here for the DAT, we will show you the equipment and answer questions that you may have about the nature and the purpose of the DAT procedure. Please contact us at (617) 355-5685 if you have any questions prior to the visit.

Electroretinogram (ERG) - awake Top

Description and Purpose:
This is an eye test that evaluates the function of the film (retina) that lines the inside of the eye. The processes that start vision take place in the retina. The retina is the most metabolically active tissue in the body. The ERG test helps diagnose diseases limited to the retina, and also diseases that affect parts of the body other than the eye.

The idea of the ERG test is that when flashes of light come to the eye, the rods and the cones and the other cells in the retina make tiny amounts of electricity. If we know exactly how much light comes to the eye, and how much electricity comes out, we can figure out how the cells, including the rods and the cones, are working. To pick up the electricity that the retina makes, contact lens like electrodes are placed on the surface of the eye.

Procedure:
To prepare for the ERG test, first of all drops will be placed in your child's eye to dilate the pupils (enlarge the black spot in the middle of the eye). These drops are the same drops that eye doctors routinely use for examination of the eyes. Then we will ask that you sit with your child in a dark room for 30 minutes. This is so the eye can adjust to the darkness. It is after this period of dark adaptation that the retina gives its strongest responses. During the 30 minutes in the dark, there is a radio available. Also you may bring favorite audiotapes and player. Some children may enjoy a small snack.

After the period of dark adaptation, the actual testing is done in a dark room and takes about 30 to 45 minutes to record a full range of responses. If the range of responses is reduced, the duration of the testing will be shorter. The ERG test does not hurt, beyond the momentary stinging of the drops that are used to dilate the pupils and the anesthetic drops used just before the contact lenses are placed. The hard part of the test is holding still.

We ask parents to stay with their child all through the period of dark adaptation and the test. For infants and young children, a bottle or a pacifier can be helpful. We will also ask the parent to hold the child's hands gently so that the contact lenses cannot be touched. As with any contact lens it its possible to scrape the surface of the eye. This has not been a problem with the procedures we use. However, the precautions that we exercise are important to minimize the chance of any scraping of the eye's surface. At the end of the test, we will check the surfaces of the eyes with some yellow drops (fluorescein) to look for any signs of scraping by the contact lenses.

Results:
During the test some information about the results becomes available. We will convey this to you. However, as you will see, many records are obtained and these all have to be measured and analyzed for the final report. We will send a copy of the ERG report to you and also to any physicians designated by you.

We are happy to discuss the reports with you and your child's other physicians. When you are here for the ERG, we will show you the equipment and answer questions that you may have about the nature and the purpose of the ERG procedure. Please contact us at (617) 355-5685 if you have any questions prior to the visit.

Electroretinogram (ERG) - under anesthesia Top

Description and Purpose: This is an eye test that evaluates the function of the film (retina) that lines the inside of the eye. The processes that start vision take place in the retina. The retina converts light to small electrical signals that can be sent to the brain. The retina is the most metabolically active tissue in the body. The ERG test helps diagnose diseases limited to the retina, and also diseases that affect parts of the body other than the eye.

The idea of the ERG test is that when flashes of light come to the eye, the rods and the cones and the other cells in the retina make tiny amounts of electricity. If we know exactly how much light comes to the eye, and how much electricity comes out, we can figure out how the cells, including the rods and the cones, are working. To pick up the electricity that the retina makes, contact lens like electrodes are placed on the surface of the eye.

It may not be possible for a child to hold still for the contact lenses and flashes of light. For these children, the ERG may be best done under anesthesia. The anesthesia doctors determine the appropriate anesthesia. Depending on your child's medical condition, it may be important to have a pre-anesthesia consultation with the anesthesia doctors.

Procedure: To prepare for the ERG test, drops will be placed on your child's eye to dilate the pupils (enlarge the black spot in the middle of the eye). These drops are the same drops that eye doctors routinely use for examination of the eyes. Another important preparation is to have the eyes well adjusted to darkness. This is accomplished by covering the eyes with eye patches.

As with the use of any contact lens, there is a risk of scraping the surface of the eye; this is called a corneal abrasion. We take a number of precautions to minimize the risk of abrasion and it is unlikely that an abrasion will occur. In the event that an abrasion occurs, it will be treated promptly. In the recovery room, it is important that your child not rub his/her eyes as this too will help minimize the risk of abrasion.

The time in the operating room is approximately one hour. This includes time to establish the anesthesia, the ERG test, the examination of the eyes and reversing the anesthesia. The actual ERG test time is 20-30 minutes.

Results: Immediately after the test, some information about the results is available. We will convey this to you. However, the final report depends on measurement and analysis of the ERG records. We will send a copy of the ERG report to you and also to any physicians designated by you.

We are happy to discuss the reports with you and your child's other physicians. We are glad to discuss the ERG test with you and answer questions. Please contact us at (617) 355-5685 if you have any questions prior to the visit.

Sweep Visual Evoked Potential (SVEP) Top

The SVEP is used to measure visual acuity, that is, vision for detail and patterns. In adults, visual acuity is measured with lines of letters. The SVEP measures acuity by assessing the response of brain waves to moving black and white stripes. The SVEP acuity test is, perhaps, most helpful in those youngsters for whom behavioral measures (Preferential Looking) give ambiguous or incomplete information about visual acuity.

To do this test, your child will be positioned to view a monitor. Moving ("sweeping") black and white stripes will be shown on the monitor. Your child may sit on your lap or in a chair.

In this test, the vision of the stripes is passed from the eye and along the visual pathways to the visual part of the brain. The procedure is designed to find the finest black and white stripes that produce a reliable response.

To do this test, small metal discs, about the diameter of the tip of the little finger, are placed on the head. The discs are connected to a computer by fine cables. The discs are held in place on the head by a paste that looks a lot like toothpaste. Three discs are placed at the back of the head, one disc is placed on top of the head and one is placed on the forehead. A band is wrapped around the child's head to hold the electrodes in place during the test.

Although the test doesn't always take the full amount time, we allow an hour for the test to be done. This includes the time it takes to place the metal discs and to accommodate for wiggly or intermittently inattentive children. Often, because of the child's eye condition, it is important to test the vision of each eye separately. To do this, we place a patch over one eye while the other is being tested.

We know the visual acuity portion of the results at the time of the visit. After the recordings are completed, the records are analyzed and the final results are included in the written report of the visit. The report will be forwarded to you, and also to any of your child's doctors as designated by you. We are more than happy to discuss the report with you and your child's other physicians.

When you are here for the SVEP, we will show you the equipment and answer any questions you may have about the nature and purpose of the procedure. Please contact us at 617-355-5685 if you have any questions prior to the visit.