There is a simple plan which persons who write or read much should adopt as being highly serviceable in preserving the powers of their vision. It is that of raising their eyes from their work at short intervals, and fixing them upon the cornice of the ceiling at the further end of the room, and if there he a pattern, making it out. This exercises the eyes at the focus for distant objects; and, simple as it is, is of great use in preventing nearsight.
There is a form of myopia of which we have seen several examples, and which is deserving of attention. It occurs in young persons, and leads to unmerited punish ment. The youth does not hold his book so near the eyes as to attract attention, and reads fluently at perhaps eight or ten inches ; but he cannot see objects distinctly at twenty feet. Such young persons have been brought to its under the impression that they were " sham ming;" but careful investigation convinced us that such was not the case: Great responsi bility attaches to the advice given in a case of this description, as on it depends much of the comfort of the individual during life. He should by no means be allowed glasses, as they would most assuredly confirm the mis chief. His books should he of large type ; he should frequently rest his eyes when study ing ; should be mach in the open air ; and the eyes should be often bathed with cold spring water.
Presbyopia (-rrpirrOus, old ; 16*, the eye) is that condition of vision in which objects are not distinctly perceived unless they are at some distance from the eye. Although not neces sarily confined to advanced years, it is one of the changes which warn the individual that the prime of life is past, as it usually com mences about the age of forty.
To a person in whom presbyopia is com mencing, distant objects appear as clear and sharply defined as ever ; but reading. writing, and working, especially by candlelight, be come irksome and distressing. The eyes feel strained, and there is uneasiness over the brow sometimes amounting to headach ; the page of a book appears misty, the type con flised at the ordinary reading distance, and a strong light is indispensable. The person therefore draws the candle to him, and holds the book close to it nearly at arm's length, throwing his head back to increase the dis tance.
These symptoms are the result of changes in the eye which cause the converging rays of light to be brought to a focus beyond the retina, upon which a confused and imperfect image is consequently depicted. They may be
the result either of flattening of the cornea or the crystalline lens, diminution in the density of the humors, or diminished curvature of the retina. Absence of the .crystalline lens pro duces the same effect in an extreme degree.
The explanation of the feelings of dis comfort, and other preshyopic symptoms, is simply this—the object being removed to a greater distance than is natural, the visual angle is reduced in size, the picture on the retina diminished, and the quantity of light becomes less: hence the retina, with its some what impaired sensibility is unable to appre ciate the object without effort, and a con siderable increase of light.
The necessity for this increased quantity of light is a frequent cause of amblyopia super vening upon presbyopia, for a very large number of work-people pursue their avoca tions in densely crowded and ill lighted rooms, and they are obliged to struggle on despite of their failing sight. Dr. Sichel states that one of the causes which renders amblyopia in connection with presbyopia so common in the conciergeries of Paris is, that the majority of persons are tailors and shoemakers, who almost without exception inhabit confined rooms called loges, into which light and air can scarcely penetrate. Presbyopia may be con genital, and it is frequently excited in persons under thirty; by the injurious habit of wearing convex glasses, miscalled "preservers." Among the lower and even the middle classes the belief is general that if from any cause the sight is weakened, such glasses are beneficial, an impression most fallacious. It however answers the purpose of some advertising op ticians to encourage the idea, regardless of the consequences to their victims.
M. Desmarres states* that country people are almost all attacked with presbyopia at an early age, because their sight is much exer cised on distant objects, and very little on near objects, whereas the dwellers in towns are attacked later in life. It may be so in France, but is certainly not the case in Eng land. The same writer affirms that this im perfection in sight is rife in countries wlicre the light is very bright.