HUMAN VISION

Wanganui Chronicle, Volume LXXXIII, Issue 19562, 4 May 1926, Page 8

HUMAN VISION

STRUCTURE OF EYE ADDRESS TO ROTARY CLUB FASCINATING SUBJECT That wonderful, complex structure. the human eye, was described by Rotarian D. A. C. Lilburne in an enjoyable address to the Wanganui Rotary Club yesterday. Illustrating his remarks with a large model, Air Lilburne referred first to the bony cavity which shelters the eye. This orbit is padded in protective fat, allowing the spherical eyeball, which is controlled by strong muscles, facility of movement. Large Eyes.

About an inch in diameter, the individual eyeball varies little in size, th' ugh the extent to which some expose the eyeball between the lids causes ’.hem to be termed the possessors of big

The white of the eye, said Afr Lilburne, is a tough fibrous membrane, the sclerotic, which in Negroes, owing to the presence of pigment, bears a yellowish tint. Merging into the sclerotic is the cornea, a transparent film through which the iris and pupil can be seen. Within the sclerotic is the choroid, a layer of bloodvessels and pigment cells, which excludes light reflections inside the eye, and furnishes nourishment to the whole of the eyeball. The Cilary Processes. Within the choroid is the sensitive cilary processes, a series of involuntary muscle fibres which play a large part in the adjustment of the lens for sight at various distances. The lens is attached to the cilary processes by suspensory ligaments, and hangs immediately behind the iris, the delicate structure which gives each eye its special colour. Both the lens and the iris float in the aqueous humour, a thin transparent liquid occupying the anterior portion of the eye, behind the cornea. The function of the iris, with its. radiating and circular fibres, is to admit more or less light to the eye. Its involuntary opening and closing, in darkness or in bright lights, causes the pupil of the eye to dilate or contract. The lens, which is convex on both sides, is subject to similar adjustments, to enable it to focus images directly on to the retina, which is the inmost coating of the eyeball. Sensitive Retina. Receiving the image from the lens, the retina conveys the sight impression to the brain. Exactly how it does it —to what stimulus it so infallibly reacts —has not been learned. Only one ore-hundredth of an inch in thickness it is yet composed of several fibrous layers, giving it a pinkish hue. Most important in its formation are the rods and cones, ultra-sensitive structures recording the sight impression for transmission to the brain along the optic [ nerve, of which the retina is, in effect, an expansion.

Within the retina, occupying the anterior chamber of the eyeball, is the vitreous humour, rather like the white of an egg, and perfectly transparent, so that it offers no obstruction to the passage of light images from the lens to the retina. Each structure of the eye, said Afr Lilburne, may be compared with part of a camera. The lens of the eye and the lens of a camera correspond. The choroid is the black lining excluding light, the retina is the sensitive photographic plate, on which impressions are regisered. Admission of Light. Even the iris has its counterpart, for every camera has a device to admit more or less light to the lens. Unlike the lens of the eye, the camera lens cannot adjust its shape and power for various tasks, but as the individual grows older the lens of the human eye becomes denser with age—generally at about the age of 40 or 50 —and the change brings on the condition of presbyopia, for which the victim requires spectacles. Air Lilburne touched on the more common forms of eye-trouble, and also described the eyebrows, with their protective hair, the lids which veil the eye, and the tear glands, which secrete moisture flowing continually over the front of the eyeball. The brows counteract the light, and incidentally arc powerful organs of expression, showing anger, suspense, contempt, and other emotions. Afr Lilburne’s interesting address on a fascinating subject was listened to with the greatest interest, and a vote of thanks was tendered him by acclamation.