Electrophysiological examination of vision

Special tests for objective assessment of visual function are performed in Athens Eye Hospital. These electrophysiological tests are conducted according to the standards of the International Society for Clinical Electrophysiology of Vision (ISCEV) by specially trained staff and are diagnosed in conjunction with the further clinical image by an ophthalmologist specialized in this field.

Electrophysiological tests provide us with objective information related to the operation of the visual pathway from the eye to the brain (visual pathway is called the path crossed by a light stimulus from the eye in order to reach the center of our vision in the brain). The function of our vision, in order to be complete, requires a sequence of structures and physiological functions that are inextricably linked, and start from the eye itself and end in cerebral cortex, which is the center of the brain, responsible for our vision. Full electrophysiologic testing is required to detect damage to any part of the visual pathway. Furthermore, there are several diseases according to which the eye is displayed normal during eye examination, while the eye cell function is impaired, whereas this is detected only after electrophysiological examination. Also, young children or people with communication difficulties, where the recording of visual function is difficult, electrodiagnostic tests provide us with clear information on the visual function of these patients.

Indicative eye diseases where electrodiagnostic tests are important for the clinical approach are the following: Retinal dystrophies such as retinitis pigmentosa, congenital amaurosis by Leber, the chorioeideremia, congenital retinoschisi, the syndrome S cones, the cones dystrophy, Stargardt disease, syndrome Usher, congenital stationary nyktalopia, Best disease, the fundus albinpunctatus disease and syndrome Bardet-Biedl. In addition electrophysiological examination is important for diagnosing eye diseases which are not genetically determined, such as toxic retinopathy, paraneoplastic syndromes, non organic loss of vision, uveitis with retinal detachment and opacities in refractive media and finally, cases of visual impairment in neonates with possible retinal damage.

The electrodiagnostic tests are the following:

1. Flash full field electroretingram:  consists the main consideration for the diagnosis of diseases of the retina, such as retinitis pigmentosa and cone dystrophy, and the macular dystrophies (e.g., Stargardt disease, etc. ). The test protocol of Electroretinogram is transacted in such a manner so that the recording of the electrical activity permits examination of the integrity of the two separate photoreceptors of the retina (cones and rods) while separation of different types of cones (eg S-cones ) is also possible.

2. Pattern electroretinogram. Pattern electroretinogram reflects activity in the ganglion cell layer and consists a specialized examination in cases where it is necessary to control the central vision, ie the function of the macula. The visual stimuli that are commonly used are consisted by "boards" (black squares) of alternating form. The measurements are performed separately for each eye and the test is widely used to approximate related maculopathy.

3. The multifocal electroretinogram Mf electroretinogram is used to control the function of the central retinal area (the 30th) and therefore the approximation of macular diseases but is also used in cases where there is too-macular loss of sensitivity of the cones.

4. The electro-ophthalmogram (EOG): EOG is used to check the integrity of the pigment epithelium. It is a specialized examination for patients who suffer from Best disease.

5. The Visual Evoked Potentials (VEP) or Occipital Lobe Evoked Potentials (E.P.O.L.) record group responses of ganglion cells of the pre-cortical visual pathway and the brain neurons of the occipital lobe. Therefore they are used in the diagnosis of diseases of the optic nerve. Stimuli "boards", as in the examination pERG, are used to examine the E.P.O.L., or a diffuse light stimulus. Contact electrodes placed on the scalp are used for this examination. They are considered the specialized examination in order to approach the optic neuritis.

Frequently asked questions by patients

What exactly are the electrodiagnostic examination of the eye and how do they correlate with vision?

These tests are consistent with the cardiogram, ie as the cardiograph measures the electrical activity and thus the functioning of the heart, in the same way the electrophysiological tests record the electrical activity of the eye and therefore its function. Following these tests it is possible to determine whether any part of the visual pathway is functioning improperly, for example, the retina, the optic nerve or nerve cells in the brain.

Why are these tests important? 

ERG and VEP tests are particularly useful in infants or children who are unable to tell us or show us how well they can see. They are also very helpful if the doctor can not find a plausible reason why someone can not see very well, something is especially common in the early stages of genetically determined diseases of the eye.

Are there risks?

These examinations are held daily in the clinic by trained personnel and are non invasive. Local anesthesia with drops is only required. Electro-retinogram examinations require also to use eye drops for dilation of the pupil. In case of children examination the support and cooperation of parents is very important and helps extremely to perform these tests quickly and with the least possible inconvenience. In cases where cooperation with / patient is not feasible, there is the possibility of conducting the examinations under general anesthesia.

What exactly happens during the test?  

Before inserting the electrodes, we clean the skin from surface cells, skin cells, small areas on the scalp or temporal area with a cotton swab with a gel that has a slightly grainy texture. This gel improves contact with the skin and helps to take good quality signals. In order to perform IQM examination an electrode is placed on the back of the scalp and two on the front. In order to perform Electroretinogram, two disposable adhesive electrodes are placed in the temporal region, and an active electrode in the conjunctival sac (i.e. inside the lower eyelid) in each eye. All the electrodes are easily removed at the end of the examination. During the examination diffused light stimulations (similar to a camera flash), are used to record the function of the cells responsible for our vision.

Do I need to hold something for the test?

It is essential to keep your glasses (distance and reading glasses) for examination and your sunglasses for the period after the examination (especially on sunny days). We also recommend that you are aware of the complete health history of the patient and to keep all ophthalmologic examinations which have been carried out in the past.