الفهرس 
Anatomy of the RetinaOnly 14 pages are availabe for public view
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Abstract
The electroretinogram (ERG) is a mass potential, which reflects the summed electrical activity of the retina. Full-field electroretinography is a well-established clinical technique for evaluating global retinal function. A limitation of the traditional global or full-field ERG is that the recording is a massed potential from the whole retina.
Unless 20% or more of the retina is affected with a diseased state the ERGs are usually normal. In other words a legally blind person with macular degeneration, enlarged blind spot or other small central scotomas will have a normal full-field ERG. So, the multifocal ERG (mfERG) technique was developed by Erich Sutter to provide a topographic measure of retinal electrophysiological activity.
Erich Sutter adapted the mathematical sequences called binary m-sequences creating a program that can extract hundreds of focal ERGs from a single electrical signal. This system allows assessment of ERG activity in small areas of retina. With this method one can record mfERGs from hundreds of retinal areas in a several minutes.
ERG electrodes are used to record ERGs from the cornea from a dilated eye. Small scotomas in retina can be mapped and degree of retinal dysfunction quantified. With this technique, many local ERG responses, typically 61 or 103, are recorded from the cone-driven retina under light-adapted conditions.
The International Society for Clinical Electrophysiology of Vision (ISCEV) published guidelines then standards to define minimum protocols for basic clinical mfERG recording and reporting so that responses can be recognized and compared from different laboratories worldwide.
mfERG allow a topographic map of local ERG activity to be measured. In general, an abnormal mfERG indicates that the foveal cones and/or bipolar cell layers are dysfunctional and the source of vision loss. mfERG is most useful in solving the common puzzle of a patient with poor vision who has a normal appearing retina.
This test helps us discriminate between optic-nerve and retinal disease, detect early hydroxychloroquine toxicity, diagnose and distinguish between the various white dots syndromes and follow patients with inherited retinal diseases who have extinguished Ganzfeld ERGs. Unlike the focal ERG, mfERG also indicates the precise distribution of the retinal dysfunction.
This precision helps correlate electrophysiologic findings with visual field testing.While we have used it to confirm non-organic visual loss, we have found it more relevant in the diagnosis of focal cone dystrophy and other similar disorders where mfERG is often the only abnormal test .mfERG can be used to:
1-Excluding Outer Retinal Disease
The neuro-ophthalmologist is routinely faced with deciding whether a visual defect is due to damage to the outer retina (before the ganglion cells) or damage to the ganglion cells and/or optic nerve. The mfERG can be very helpful, especially in situations where standard tests provide ambiguous information. Because damage to the ganglion cells or optic nerve does not decrease the amplitude of the mfERG, an abnormal mfERG provides strong evidence for an outer retinal lesion.
2-Differentiating Among Retinal Diseases
The mfERG can help to differentiate among retinal diseases based on changes in the relative amplitudes and latencies of N1 and P1. A large delay in the timing of the mfERG is associated with damage to the photoreceptors/outer plexiform layer. Damage to bipolar, amacrine, or ganglion cells yields relatively small changes in the implicit time of P1 and may even shorten it.
3-Following Disease Progression and monitoring treatment efficacy
Because the mfERG shows good repeat reliability, it can be used to follow the progression of a disease. This is particularly helpful in the case of patients who are poor field takers. It can be of value in monitiring treatment efficacy and in detecting drug toxicity.
4-Differentiating Organic from Nonorganic Disorders
The mfERG can be used to diagnose nonorganic disorders. The advantage of the mfERG over the conventional ERG is that it provides a topographical representation that can be compared with the patient’s visual fields. A normal mfERG does not, by itself, establish a visual deficit as nonorganic. If the mfERG is normal, then a multifocal VEP should be performed as well to rule out damage to the optic nerve/ganglion cells.