EYES AND EYESIGHT

Southland Times, Issue 21716, 31 May 1932, Page 3

EYES AND EYESIGHT

AN INTERESTING LECTURE. NATURAL PHILOSOPHY CLUB. An interesting and instructive lecture on “Eyes and Eyesight” was given by Mr E. C. Marshall before a large and appreciative audience at the meeting of the Natural Philosophy Club of the Boys’ High School held at the school last Friday evening. Mr Marshall commenced by discussing various theories concerning the nature of light, and showed how light travelled in straight lines in a medium such as air, but when passing from one medium to another, such as from air to water, or from air to glass, the light rays were bent, or refracted, in accordance with definite laws.. Thus rays of light from an object in front o r a glass lens were refracted by the ■ lens, and bent round to form an image or picture of the object on a screen placed behind the lens. In the same way, explained Mr Marshall, light rays on entering the eye were bent by the refracture system of the eye, consisting mainly of the crystalline lens, and thus a picture was formed on the back portion of the eye, known as the retina. Tire retina consisted of various types of nerve endings whereby the picture was ultimately conveyed to the brain by means of the main optic nerve. The effect of the lens system of the eye, said the lecturer was to invert the picture, and consequently everything was really seen upsidedown. In order to convince the audience of the truth of this somewhat startling statement, Mr Marshall described a very simple experiment with a pin and a hole in a piece of cardboard whereby this fact could be easily demonstrated. Dealing .with the common defects of vision, the lecturer explained that in the case of short-sight and long-sight (known technically as myopia and hypermetropia respectively), the image was not brought to a focus exactly upon the retina. In myopia the eye was too long from front to back, and consequently a concave, or hollow, spectacle lens was necessary in order to make the rays diverge more before entering the eye, and thus throw the image further back so that it would fall upon the retina. In the case of long-sight the eye was too short from back to front, and the necessary correction was supplied by means of a convex lens. Mr Marshall referred also to several other common eye troubles, including that of glaucoma, from which the British Prime Minister, Mr Ramsay Macdonald, was recently reported to be suffering. Glaucoma, explained Mr Marshall, was due to the blockage of certain small canals which acted as a drainage system for the eye. Owing to this blockage the pressure inside the eye became too great, and ultimately tended to force the optic nerve back from the retina. This necessitated a surgical oneration in order to relieve the pressure. Mr Marshall concluded his lecture, which was illustrated throughout by diaerams, by describing the . anatomy of the human eye, and explaining the function of each component part. . A very fine model was exhibited, which could be taken to pieces, thus enabling each part to be examined in detail. The model also showed the various intricate r .uscles controlling the movements of the eye, and the system of blood vessels conveying tf'ie supply of blood. At the conclusion of the address Mr Marshall was accorded a hearty vote of thanks by acclamation.