The illustrated optical manual, or Handbook of instructions for the guidance of surgeons in testing quality and range of vision, and in distinguishing and dealing with optical defects in general / by Surgeon-General Sir T. Longmore.

Thomas Longmore

Date:: 1888

Credit: The illustrated optical manual, or Handbook of instructions for the guidance of surgeons in testing quality and range of vision, and in distinguishing and dealing with optical defects in general / by Surgeon-General Sir T. Longmore. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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$blurring from diffusion owing to similar myopic conformation of the eyes. This circumstance results from the fad that absolutely ] infect definition of a retinal image is not neces-ary for recognition of an object. There are few, if any. eyes which can see a star as the luminous orb which it is. All the other conditions, too, on which acuteness of vision depends, besides perfect definition of retinal images, are subject to variations in different individuals. Differences exist in the power of preventing peripheral rays from entering the eyes as well as of eliminating the confusing effects of diffusion of retinal images, in habits of observation of objects. quickness of perception, and other influences of the kind. But taking the average of a number of trials, at about the ordinary ages of recruits, I have found that persons affected with uncomplic M.= 1*75 Dean manage, with each eye singly, to count the test-dots at 10 feet under suitable exposure in good daylight. The test-dots are seen mistily; they may appear more or less altered in form, but they can be sufficiently distinguished to admit of being counted. The present test-dot standard for vision of recruits, therefore, admits men with an amount of M. = 175 D, and with visual acuteness less than \ Sn. (J^). It will usually exclude degrees of M. higher than 1*75 D. 33. The Qualities of V. which are needed in different Parts of an Army.—The M. which would make a man unsuitable for the duties of one arm of the service may not make him unsuitable for another. The M. which would unfit a soldier for aiming at long ranges, whether with a rifls or a field gun, or for the duties of a cavalry vidette, would not unfit him for the working duties of a sapper or pioneer, or for those of the commissariat and transport corps, or medical staff corps. Just as there are different standards of height, girth of chest, &c3 for the men of different pa] the army, so equally necessary appear to be different standard- of V. to fit them for their special duties. Certainly riflemen, artil- lerists, and cavalry soldiers, ' the eyes of the army, should especially be as free as possible from short-sightedness, hypermetropia, and other defects of vision. What particular degrees of M. and H., however, should exclude men from special parts of an army in which very acute vision, and a long visual range, are essentially important, can only be determined after a definition by military authority of the exact requirements in those several parts of the service. It is the pro- vince of the military authorities to settle the degrees of V. which are necessary for the military duties and responsibilities demanded from soldiers in each branch of the military service: it is the province of the medical officer to ascertain that the men possess the precise degree of V. which is ordered. At present, in the enlist- ment of recruits for the British army, the same orders in reaped to$