Arden ratio (AIPG 2010)
1. The electroretinogram (ERG) is the record of an action potential produced by the retina when it is stimulated by light of adequate intensity.
2. The normal ERG is biphasic.
a. The a-wave is the initial fast negative deflection directly generated by photoreceptors.
b. The b-wave is the next slower positive deflection with larger amplitude. Although it is generated from fluxes of potassium ions within and surrounding Muller cells, it represcents the activity of lipolar cells
3. Normal ERG:
a. Scotopic ERG
b. Photopic ERG
4. Multifocal ERG
5. Multifocal ERG is a method of producing topographical maps of function of entire retina
EOG : Measursement of resting potential of the eye.
The normal value is over 1.85 Ardens ratio light peak and dark trough
Fig: Components and origins of the electroretinogram
Visual evoked potential
1. Principle. The visual evoked potential (VEP) is a recording of electrical activity of the visual cortex created by stimulation of the retina. The main indications are assessing of visual function in babies
2. Interpretation: In optic neuropathy there is proloned of latency and decreased in amplitude.
1. The visual field
2. The outer aspect of the visual field extends approximately 60o superiorly, 60o nasally, 80o inferiorly and 90o temporally. The blind spot is located temporally between 10o and 20o.