Download e-book for iPad: Electrophysiology of Vision: Clinical Testing and by Byron L. Lam

By Byron L. Lam

ISBN-10: 0824740688

ISBN-13: 9780824740689

ISBN-10: 0849344948

ISBN-13: 9780849344947

Written via an skilled clinician and researcher within the box, this reference offers functional details at the medical recording recommendations, physiologic origins, and functions of electroretinogram (ERG), electro-oculogram (EOG), and visible evoked capability (VEP) checks.

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13). The Naka–Rushton function describes only the first limb of the scotopic intensity-response, and more complex equations are required to describe both limbs of the function. Hood and Birch point out that Naka–Rushton fits are better understood in the context of a dynamic model and should be interpreted with care (53). The b-wave may be a very poor reflection of inner retinal activity when the inner retina is affected by disease, and the b-wave implicit time provides a measure of photoreceptor sensitivity.

The b-waves of flicker stimuli are made of ON- and OFF-ERG components with large phase differences so that these components partially cancel each other (31,32). Oscillatory Potentials: Physiologic Origin The oscillatory potentials consist of about 4–6 wavelets during the ascending phase of the b-wave and have physiologic origin that differs from the a- and b-waves (33,34). The oscillatory potentials are due to both rod- and cone-generated activities and can be recorded in scotopic as well as photopic conditions (35,36).

This asymmetric distribution reflects the asymmetry of the visual field and accounts in part for the relatively shortened nasal field. Dark and Light Adaptation The sensitivity of the photoreceptors adapts dramatically over a wide range of light levels. The cones dark-adapt more rapidly than the rods and reach maximal light sensitivity after 10–12 min. The rods dark-adapt at a slower rate but reach a plateau of much higher light sensitivity after 30–40 min (Fig. 23). Under scotopic conditions, the rods are 100- to 1000-fold more sensitive to light than the cones, and a dim flash stimulus activates only rods.

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Electrophysiology of Vision: Clinical Testing and Applications by Byron L. Lam


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