On examining the records, he found that of 117 miners treated by him on account of nystagmus, 107, or 91.4 per cent, used safety lamps, whereas in two mines using open lamps and employing 772 men, only 0.35 per cent was found to be afflicted with nystagmus. He points out, however, that it was not only the insufficient illumination derived from the Davy lamp, but also its imperfect construction as regards the largest amount of possible effective illumination that was to be held responsible as a causative factor in nystagmus.

The relative frequency of this disease is referred to by Shufflebotham as follows: "

a

Dr. Court has stated, as a result of the examination of several thousands of workmen, that 35 per cent of coal getters are subject to this disease to some extent. Snell estimated that 5 per cent of all colliery workers were affected, but he did not discriminate between different kinds of work in the coal pit. Nieden, who examined nearly 30,000 coal miners, agrees with Snell that the frequency of nystagmus in underground workers is somewhere about 5 per cent. In the north of France Dransart and Famechon have given 10 per cent as the number affected. Romiée and Thiebert, of Liege, during 1908 and 1910 examined 5,000 workmen in 27 collieries. More than three-fifths were coal getters, and on the average 21 per cent were affected with symptoms of nystagmus; in collieries lighted by lamps burning heavy oils 37 per cent of the coal getters were affected. Romiée had made a similar inquiry in the same district in the years 1877-78, and the result of his later inquiry was to show a marked diminution in the number of cases as well as in the severity of the symptoms. Stassen, who in 1909 examined 3,385 colliers descending into the pit, and also on their return to the surface, found that 15 per cent of the workers were affected before commencing their work and 22 per cent at the end of the shift.

Roger, of Hondeng-Geognies, as a result of examining over 7,000 workmen, came to the conclusion that 17.5 per cent were suffering from nystagmus. Liebert, the chief inspector of mines to the Belgian Government, found different percentages of miners affected in different districts. In one series of examinations which he conducted with the help of Romiée and Thiebert he found that of 305 workmen examined in one pit 73 were affected with miners' nystagmus, giving a percentage of 23.9, and he refers to a memoir dealing with 3,685 workmen, among whom 704 showed symptoms of this disease, or a percentage of 19.1.

OTHER EYE DISEASES OF MINERS.

Aside, however, from the question of imperfect or insufficient illumination, Nieden found that in a preponderating number of cases the miners suffered from other eye afflictions, including trachoma, dimness of the cornea, chronic iritis, irido-choroiditis, atrophy of the optic nerve, etc., all of which, of course, would predispose to nystagmus under the special conditions of underground work at the face of the seam. The only specific suggestion that he makes as regards prevention is the necessity for better artificial illumination by means of safety lamps, and he refers to electric mine lamps used in the Newcastle (England) district, but these, of course, do not indicate the presence of dangerous gases.

a Shufflebotham, Frank, The hygienic aspect of the coal-mining industry in the United Kingdom: Brit. Med. Jour., Mar. 21, 1914, p. 648.

Nieden, A., Der Nystagmus der Bergleute, Wiesbaden, 1894.

CONCLUSIONS OF LINDEMANN.

On the occasion of the Fifteenth International Congress on Hygiene and Demography, Lindemann, chief medical director of the Bochum Miners' Union, contributed an address on the occupational diseases of miners, in which the subject of nystagmus is briefly referred to. He admits that the disease is of comparatively common occurrence, and points out that general debility, anemia, and alcoholism may be contributory causes, aside from the high underground temperature and excessive muscular strain. He dissents from certain conclusions by Snell with regard to the inability of miners suffering from nystagmus to recognize in time the blue cap on the safety lamp, indicating dangerous gaseous conditions. According to his own investigations, miners suffering from nystagmus were, without exception, able to determine the presence of fire damp to the extent of 2 to 3 per cent with absolute certainty. He refers to the rule of the Allgemeiner Knappschafts Verein zu Bochum (Bochum Miners' Union) (which is the compulsory miners' insurance association) that miners afflicted with nystagmus are not permitted to work underground, and that nystagmus itself entitles to compensation, both as regards money payments for support and medical treatment, as well as an invalidity pension. He states that an additional rule is to the effect that miners whose normal vision has been reduced 50 per cent are not permitted to work underground. As regards treatment, he states that good results follow only when underground work is discontinued at an early stage of the disease.

In this connection a brief reference may be made to the recently published experience of the Bochum Miners' Union for the year 1912, as regards the frequency of nystagmus as a cause of invalidity. Out of 3,605 cases of invalidity, 649, or 18 per cent, were on account of nystagmus, and 75, or 2.1 per cent, on account of other diseases of the eye. As the membership of the fund for the year 1912 was 376,000, this would be equivalent to an invalidity rate on account of nystagmus of 1.73 per 1,000 employed.

The foregoing preliminary observations emphasize the practical importance of nystagmus wherever the disease prevails to a considerable extent. A strictly localized investigation should limit itself to a mining district in which the miners use safety lamps and undercut the coal with the pick.

a Lindemann, Wilhelm, Über die Unglücksfälle und Berufskrankheiten der Minen und Tunnelarbeiter: Trans. Fifteenth Int. Cong. on Hygiene and Demography, vol. 3, 1913, pp. 673–690.

• Verwaltungs-Berichte, Allgemeiner Knappschafts Verein zu Bochum, 1912, Bochum, Germany, 1913.

NYSTAGMUS AS A MINING PROBLEM.

Nystagmus is not referred to in the "Report on Mining Methods and Appliances Used in the Anthracite Coal Fields," a published by the Second Geological Survey of Pennsylvania in 1883. There is also no reference to the disease in the section on "Hygiene of Occupation" published in Buck's "Hygiene and Public Health," in 1879. The importance of the disease has come to the front as a practical question in mine management only since the adoption of the workmen's compensation act in England of 1906 and the inclusion of nystagmus in the schedule of occupational diseases for which compensation is required to be paid. In a treatise by Cockin it is said under "Nystagmus" that

This is a disease which affects the nerves of the eyes; it is more prevalent among those who work by the light of safety lamps than among those who use naked lights. The cause of nystagmus is thought to be either the constant dazzling of the eyes by the bright concentrated light of safety lamps or the strain put upon the muscles of the eyes by work, such as holing. The symptoms of this disease are a twitching of the eyes and impaired sight.

This inadequate reference emphasizes the lack of appreciation of the importance of an affliction that may be much more common in this country than is generally supposed. As there is unquestionably close interrelation between nystagmus and the use of safety lamps, it is regrettable that the extended consideration given to this part of mine equipment in most of the textbooks on coal mining should be practically without useful references to the prevention of a disease which, wherever it occurs, is, without question, a most serious affliction of the men employed, and an important factor of cost in mine management wherever workmen's compensation laws require compensation to be paid for cases of nystagmus directly attributable to the employment.

MEDICAL CONSIDERATIONS.

It has therefore seemed advisable to enlarge upon the medical aspects of a problem that is practically certain, in the near future, to attract attention in the United States, if only along negative lines, to prove beyond a doubt that the affliction is not as common in this country as it is known to be abroad. As pointed out in an editorial in the Journal of the American Medical Association:d

The careful study of occupational diseases is one of the features of the modern conservation movement coming with the recognition of the economic advantage which attaches to the preservation of health in the industrial population. As an instance of the financial aspects of some of these matters we may cite a recent estimate of the cost of the 1,618 cases of miners' nystagmus in the United Kingdom in 1910. The

a By H. M. Chance; 573 pp.

Buck, A. H., A treatise on hygiene and public health; Hygiene of occupation, by R. S. Tracy, vol. 2, 1879, pp. 1-96.

c Cockin, T. H., Practical coal mining, 1909, p. 405.

d Vol. 59, Aug. 17, 1912, p. 547.

compensation of these individuals is calculated at over $155,000, a figure which does not take into account the poor earning capacity of the men in the incipient stages of the disease and other profits lost by the employers. Aside from its purely humanitarian or scientific aspects, therefore, successful investigation of such an industrial disease promises to pay a rich return. This statement needs to be brought home to American captains of industry who have as yet made only a beginning in a direction almost certain to lead to a profitable outcome from every point of view.

Among miners nystagmus is an occupational neurosis characterized by an involuntary oscillation of the eye-bulbs on fixation. It seems to be confined to the workers in coal mines and prevents the miner from accurately fixing anything toward which his vision is directed. Such a disturbance of vision evidently must seriously impair the working capacity of an individual who needs to strike accurately with his pick or to match timbers well in collieries.

There are two prominent views with regard to the etiology of the disease. One of these attributes the nystagmus to the strain of accommodation in the presence of deficient light; the other view associates the disease with the positions taken by the colliers, and assumes that there is a local myopathy affecting the elevator muscles of the eye. The cause and prevention of miners' nystagmus has been investigated lately by Dr. T. L. Llewellyn. It is a striking fact that the disease does not occur in the metalliferous mines where safety lamps are not required. In mines where candles can be used or where electric lamps are in operation nystagmus is not found. Now the safety lamp gives much less light, quickly becomes dirty, throws shadows, and must be placed out of the reach of the picks. We are apt to overlook the amount of our light which is due to the diffuse reflection from the walls of the room in which we happen to be. In the coal mine practically all of the light is absorbed; hence the need of satisfactory sources of illumination.

The disease is shown to attack the men who use their eyes in a much larger proportion than the other men. A large proportion of them suffer from errors of refraction. All have weakness of accommodation. Llewellyn regards nystagmus as a disease of great complexity and one in which many factors are at work. The chief of these is strain caused by deficient light. He believes that, as the result of working for long periods in the comparative darkness of the pit, the cells of the retina probably lose their power of producing sufficient pigment for exact vision. This failure occurs sooner in fair blue-eyed people and in those who are subject to a greater eyestrain, owing to errors of refraction. The more frequent occurrence of nystagmus in winter, the loss of visual acuity, the dread of light, are all points in favor of this theory. Another is the oblique position in which the head is held in many cases, whereby an attempt is presumably made by the patient to bring a fresh part of the retina into action. Darkness itself, Llewellyn suggests, is not enough to set up nystagmus.

Here are the preventive measures proposed: No man with refractive errors should be allowed to work underground and no man should be employed without medical examination. Above all, however, comes the improvement in the lighting power of the miner's lamp. If possible a lamp giving a diffused light should be introduced. Improved ventilation also means a better light. The study of the introduction of electric lamps promises to be of great interest in this connection.

CONTROVERSIAL ASPECTS.

α

Much to the same effect is an extended editorial discussion on the subject in the British Medical Journal of April 13, 1912. The editorial draws attention to the correspondence between Markham, a coal owner, and the Secretary of State for the Home Department, arising

95027°-Bull. 93—16- -3

a Pp. 853-854.

out of a letter to Markham from Dr. J. Court, of Stavely, Derbyshire, whose views are based on 40-years' experience in coal-mining. Court urged that an inquiry should be undertaken into the eyesight of all men and boys working in collieries and other mines in Great Britain, where both naked lights and safety lamps are used, in order to ascertain (1) the cause or causes of miner's nystagmus; (2) the duration and best means of cure; (3) whether there is a constitutional liability; (4) whether one attack predisposes to another; (5) whether mild cases of nystagmus incapacitate a miner for work underground; and if so, to what extent; and (6) whether miner's nystagmus causes the sufferer to be a danger to himself and other miners at work with him. An abstract from the editorial follows:

There are two views as to the cause of miners' nystagmus. The one attributes it to eyestrain due to working in a badly lighted space with black light-absorbing surfaces; the other to strain of the extrinsic muscles of the eye, especially of the elevator muscles, due to the position of the miner when at work at the coal face, or when examining the roof of the workings to detect gas or threatening falls. The view hitherto most generally accepted is the second, a theory which brings the condition into the same category as writer's cramp and other occupational neuroses. This theory was strongly held by the late Mr. Simeon Snell, who supported it by many cogent arguments drawn from his long experience in treating eye affections among coal miners. He had the support of Nieden, Dransard, and some other continental authorities, but the theory has always been open to the objection that the disorder is seldom met with except among men working in coal mines; those engaged in other mines, it is said, are seldom or never affected in this way. In a paper on the causes and prevention of miner's nystagmus, communicated recently to the Royal Society by Dr. J. S. Haldane, Dr. T. L. Llewellyn, of Bargoed, Glamorganshire, advanced the theory that the nystagmus was due to a condition of imperfect centripetal impulses (imperfect fixation, disturbance of equilibrium, etc.), the intimate connection between the centers governing the associated movements of the eyes being lost and incoordinate movements ensuing. Dr. Haldane has informed the Home Secretary that Dr. Llewellyn's researches in a number of coal fields and also among metalliferous miners confirm Dr. Court's conclusion as to the connection between nystagmus and the very poor light given by ordinary safety lamps. Dr. Llewellyn found errors of refraction (hypermetropia, or astigmatism) present in 93 per cent of 280 cases examined, and concludes that the personal proclivity to the disorder which is undoubtedly an important factor, since only a small percentage of coal miners are affected, may be due to these defects, but he admitted that accident, shock, and ill health are also predisposing factors. He found that the disorder certainly diminished with improved illumination, being almost unknown in naked-light districts, and the principal preventive measures he indicated were improvement of illumination (which Dr. Court also advocates, suggesting the use of electric lamps), employment of coal-cutting machines in thin seams, and the elimination of unfit workers by medical examination.

NYSTAGMUS A MINE-SAFETY PROBLEM.

The practical importance of these observations is obvious. The evidence upon several important controversial points, however, could hardly be considered sufficient. Snell," in his address as president

a Snell, Simeon, President's address delivered at the seventy-sixth annual meeting of the British Medical Association: Brit. Med. Jour., Aug. 1, 1908, p. 243.