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[Date] Anatomy and Physiology of Blindness

Introduction

No one can doubt that one of nature's most precious gifts is that of sight, but there is an odd thing about vision. Everyone who sees also has a "blind spot" in the eye. This blind spot, about one -twelfth of an inch in diameter, is where the optic nerve enters the retina. Without this conjunction, the eye would not be able to see. It is the presence of the blind spot that makes vision possible. With both eyes fixed on the same object, we overcome this deficiency, for each eye compensates for the other's defect. It is only when we exercise "binocular" vision that we see objects clearly and whole, in their dimensionality.

Anatomy and Physiology of Blindness

When a trumpet produces a sound, it sets up vibrations (in the air) that are trapped by the auricle, and conducted to the tympanic membrane, that then vibrates. This causes movement of the three small bones in the middle ear that, in turn, transmit the vibrations to cause ripples in the cochlear fluid. These stimulate the hairs to move, thereby affecting the vestibulo-cochlear nerve that sends messages to the brain that recognises the sound as a trumpet blowing. Higher pitched sounds cause more hairs to vibrate than do the lower sounds. The semi circular canals respond to changes in body position and send messages to the brain, thereby helping to control balance.

For unknown reasons, people with Usher syndrome become deaf because damage occurs to the hair cells that vibrate in the cochlear fluid. This damage may increase with age. Thus, when a sound is made near the auricle, it will pass through the canal to the middle ear. However, subsequent transmission of the sound to the cochlea will be faulty and hence the sound will be inadequately passed along the vestibulo-cochlear nerve or recognised by the brain.

This is how revolutions happen- why czars an commissars and shahs are toppled almost overnight- because leaders see only what they like to and want to, believing until the last moment that their distortion is reality. History is largely a record of willful blindness by those who most needed to see straight and deep and truly. We on the lower rungs conspire in our own personal disasters in much the same fashion. We see too little, and too late -not because we lack the capacity, not because the optic has been cut, but because we prefer the comfortable illusion we have grown up on to the abrasive realities of the changing times. Each of us is born with his moral and intellectual blind spot, giving us limited (Romans 7:20-24; II Timothy 2:26) choice and too often we choose to focus the wrong eye on our fate; Luke 11:34-36; II Corinthians 2:16; James 1:9.

The retina is the sensory end of the optic nerve which branches in the eye forming three retinal layers. The lowermost layer contains rods which give brightness and darkness perception and cones for color perception. ...