Eyes (Preservation Of The). Mr. Cooper, in his " Practical Remarks on Impaired Vision," gives some excellent hints on the preservation of the eyes, which will be interesting to many of our readers. Daily experience teaches us that the decay of vision is hastened by many causes which arc frequently overlooked. Although it is about forty that the sight usually begins to fail, yet we find that some persons attain extreme old ago without needing glasses at all. Other persons, on the contrary, require glasses by the age of thirty, and, though much depends upon constitution, much also depends upon a person's habits.
One of the worst of habits is that of overworking the eyes by candle-light at night. Repose from labour, so necessary for the restoration of tone and vigour to the several organs of the body, is too sparingly granted to the eyes.
Let it be remembered that day-work is
Preferable to night-work ; that while the light of a candle or lamp is trying even to a strong eye, the moderate light of the sun is strengthening to it Those whom cir-cumstances compel to study in the evening should select that kind of work which is least distressing to the eyes; they should especially avoid indistinct writing or small print.
Reading by fire-light, or simply gazing at the tire when sitting alone, or in a contemplative mood, is highly injurious to feeble eyes, and should be avoided by all. It is not advisable to read by twilight; too little light is as pernicious as too much light, yet many persons will, evening after evening, try their eyes in this way rather than burn a candle. It is injurious to the eyes to be long exposed to the reflection of a strong light, whether artificial or natural, such as the reflected sunshine from the page of a book. Too brilliant a light produces undue excitement of the eyes. To preserve weak eyes as much as possible from a strong light neutral tint spectacles are exceedingly suitable.
In reading and writing, just that amount and quality of light, whether natural or artificial, should be allowed which, while it thoroughly illuminates the object, feels grateful and pleasant to the eyes. This desideratum can never be obtained without due regard to the position of the light. The light cast upon a hook while the candle is in front is by no means pleasant, and the glare of the flame is very trying to weak eyes. It will be found, that if the candle or lamp be placed behind the reader, a little elevated, and slightly on one side, the pleasantest and least injurious effect is produced ; for the light then reflected to the eyes is less distressing, and at the same time the eyes are perfectly protected from the heat and glare of the flame.
Sudden transitions from gloom to strong light should ho avoided. The dazzling effect produced when we come suddenly from darkness into light arises from the pupils having been widely dilated to admit the greatest possible number of luminous rays whilst in the gloom ; and as the pupil of the eye requires time to contract, sudden transitions from comparative darkness to a bright light compels the eye to admit far more rays than is either agreeable, or than it is calculated to bear without injury.
It cannot be too strongly urged upon any one about to use spectacles for the first time, that that power which will enable him to read without much exertion by candle-light is the only power suitable for him. It is by candle-light only he should use glasses at first, and as soon as he finds that he stands in need of glasses by day as well as by candle-light, and that the glasses he uses no longer afford him sufficient assistance by candle-light, it will be proper to use the next power for the evening, but for the evening only, and to allow himself the use of the others - and their use only - during the day. The greatest caution as to increasing the power of glasses should be observed, for persons who change their glasses, unnecessarily increasing their power each time, are exhausting the resources of art instead of economising them as much as possible. Optical aid can only be extended to a certain point, and the steps to that point should be as slow and as numerous as possible. By exercising prudent precautions, persons may often attain great age, and yet never require the aid of glasses beyond a very moderate power; others, on the contrary, who from ignorance frequently increase the power of their glasses, may run through the whole assortment, and leave themselves only the most inconvenient resources to fall back upon - viz. the very highest powers