SELECTION OF EYE-CLASSES.

New Zealand Graphic, Volume IX, Issue 5, 30 January 1892, Page 113

SELECTION OF EYE-CLASSES.

Never purchase glasses from a pedlar or a jeweller. Even opticians, except the most careful ones, practically allow the customer to make his own selection, and if he is nearsighted, he commonly selects glasses which are too strong, while if he is far sighted, he selects such as enlarge the print, or else are of too low a number, from the false idea that this will favour a longer preservation of his sight. Many persons suffer from astigmatism, a defect which prevents the rays of light from converging at the same focus. The trouble may be slight or severe. The afflicted person is sometimes born with it, but sometimes it develops after adult age is reached. Anyone who has astigmatic eyes should consult a skilful oculist. Sometimes there is spasm of the musclesof accommodation. In this case, the person may seem to be near sighted while really far-sighted, or greatly near-sighted while only slightly so. The oculist alone can treat such eyes.

The medical name of near-sight is myopia. In this defect the rays of light converge to a focus before reaching the retina. The opposite of this, in which the converging point is beyond the retina, is called hyperopia. Hyperopia gives rise to headaches and neuralgia, from the constant strain of the muscles of accommodation in viewing distant objects. Persons afflicted with it need convex glasses, but naturally select concave ones. The glasses should be the strongest that can be worn with comfort, and should be used all the time, both for far and for near vision. In myopia, the glasses should be the weakest that bring the sight to nearly normal vision when the print is at a distance of fourteen to sixteen inches. Many persons, when first fitted, are unable to wear with comfort any glass that makes the vision perfect. They complain of vertigo, and objects appear small and unnatural. In such cases the strength of the glass should be decreased, even though the person does not see so well. It is desirable to wear the glasses about half an hour before deciding on them. Old sight—presbyopia—begins at about the age of forty. It is first noticed by the tendency to hold the paper further off. The glasses should not enlarge the letters, out simply render them clear and natural at the ordinary reading distance. Whatever the ocular defect, the proper glasses should be obtained as soon as it is discovered.

In addition to the above defects, there may be a weakness of one or more of the ocular muscles, with a constant strain on the weaker, in order to do its full share of the work. This strain may cause severe neuralgia of the head and nervous symptoms generally. In such a case, consult a skilful oculist. In the above we have given the substance of an article in Medical Classics by Dr. Norton, professor in the New York Ophthalmic Hospital.