Walsh and Hoyt's Clinical Neuro-Ophthalmology

Section 1: The Visual Sensory System

An overview of Section 1.

"Each human optic nerve contains about 1.2 million axons, representingabout 40% of all fibers enteringor leavingthe central nervous system (CNS). When the rods and cones are added to this number, the total number of sensory units that forward visual information to the brain is increased by a factor of 80. That number is increased further when one considers the millions of axons that transmit information from the lateral geniculate body to the striate cortex and from the striate cortex to other parts of the CNS. Thus, any physician who evaluates patients with disorders of vision must have knowledge of the embryology, anatomy, and physiology of the visual sensory system. This information is covered in the first chapter of this section. The second chapter describes the principles and techniques of examination of the visual sensory system. The ophthalmoscopic recognition and differential diagnosis of swelling or pallor of the optic disc and their distinction from congenital disc anomalies are of fundamental importance not only to the ophthalmologist but also to the neurologist, neurosurgeon, and other physicians. Chapters 3-11 are devoted to the symptoms, signs, pathogenesis, and various etiologies of both anterior (with optic disc swelling) and retrobulbar (with an initially normal disc) optic neuropathies and optic atrophy and to their differentiation from congenital disc anomalies. Knowledge of the various disorders that affect the optic chiasm, tracts, radiations, and striate cortex are also important to the physician dealingwith patients complaining of visual dysfunction, as is an understandingof the so-called ‘‘central'' (also called ‘‘higher'') disorders of visual function. The last two chapters of this section deal with the features of such disorders."