overhead coal, which requires strain of the eye muscles, the eyes being constantly directed both upward and to one side. It is therefore limited to those who handle the pick exclusively. The symptom usually subsides in time after the form of work has been changed. It is at present a rare phenomenon, owing to two causes-first, the increasing introduction of machine methods and, secondly, the operation of the gross-weight law, whereby miners are paid for the gross tonnage of the coal mined, not on the basis of the size of the nuggets. When the latter system prevailed the miners sought to increase their earnings by carefully picking out large fragments of coal, which involved the ocular strain."

Thompson quotes Browne and Mackenzie to the effect that

The contributing factors in producing this symptom are: Inadequate light, errors of refraction, straining of the extrinsic eye muscles, and a neurotic temperament. Ninety per cent of their patients had errors of refraction. The symptom is often attended by severe pains in the head and eyes and by quivering of the eyelids. The miners find some relief from the affection by walking with the eyes directed downward. No special treatment, except rest, is of any avail, and after a prolonged period spontaneous recovery may take place, which may be partial if not always complete.

b

The following suggestive description of nystagmus is by Louis: Probably the most unhealthful part of the coal miner's work consists in "kirving" or undercutting the coal, in doing which the miner has to lie on his side on the floor of the coal seam, swinging his pick with a peculiar sideways stroke over his head, till he has cut out a narrow groove some 3 feet deep below the overhanging mass of coal. Work in this constrained position is necessarily harmful to some extent. Its effect has been most noticed as affecting the nervous system, and especially the nerves of the eyes, the disease known as miner's nystagmus having been often ascribed to it. Cases of miner's nystagmus occur, however, also among miners who do not have to kirve, and it may well be due in great part to the poor light obtainable in so many cases underground, especially when safety lamps are used, and the consequent strain on the eyes. At any rate this seems to be the opinion of several who have suffered from this complaint.

OCCUPATIONAL EYESTRAIN.

In the same work, in connection with a discussion of eye diseases and eye accidents in relation to industrial occupations, Snell, a recognized authority on ophthalmology, contributes an extended discussion on nystagmus, not only among miners, but also among persons employed in other occupations underground. The findings and conclusions of Snell have not been accepted in their entirety by other authorities on the subject of nystagmus, but they are given in full so as to provide the necessary basis for comparison with divergent views subsequently to be quoted.

Coal miners, as a result of their employment, are especially prone to a peculiar affection of the eyes called "nystagmus" (miners' nystagmus), which is characterized by

a Thompson, W. G., Op. cit., p. 570.

Louis, Henry, Mining: Thomas Oliver's "Dangerous Trades," London, 1902, chap. 37, p. 534.

Snell, Simeon, Eye diseases and eye accidents in relation to industrial occupations: In "Dangerous Trades," by Thomas Oliver, London, 1902, chap. 58, pp. 760-772.

95027°-Bull. 93-16-2

oscillations of the eyeball. The sufferer, too, complains of objects dancing before his eyes. In this disease objects appear to move either in a circle or an ellipse. Headache is often present, and especially giddiness, which sometimes causes the miner so to stumble about that he is compelled to leave his work in the mine. The movements of the eyeball are chiefly rotatory; to-and-fro oscillations are sometimes superadded. These are rarely vertical, but the rotatory are seldom, if ever, absent. The rapidity of the ocular motions varies greatly; from 60 to 150 motions may be counted in a minute. I have observed them as frequent as 350. Both eyes are affected, but the rapidity of movements may vary in the two eyes. The more rapid the oscillations the less extended is the excursion of the globes. The oscillations are arrested by turning the gaze downward below the horizontal line, and miners often learn to rest their eyes in this way. Looking upward, and especially obliquely to one side or the other, rapid movements of the head, lowering of the head, and suddenly raising it are means of increasing the rate of movements of the eyeballs, or, in other cases, of rendering them evident. Placing the patient in the position he would assume at his work is another method. Tremors of the head (noticeable to the hand placed on the head), of the eyelids, and of the muscles of the face or neck are often associated with nystagmus, and so is torticollis or "wry neck" in some cases. Night blindness has been alleged to be present, but there is some reason to dispute this. The nystagmus alone is a sufficient cause for any difficulty in seeing in a failing light. Errors of refraction, myopia, hypermetropia, and astigmatism are often present, but bear no causal relation to nystagmus; visual acuity is generally unaffected. Color perception is good, and, so far as the movements of the eyeballs permit of testing, the field of vision is normal. The onset of the disorder is often brought about by some attack of illness. It is generally met with in men who have worked in the mine for some years. Ninety per cent of cases occur in persons from 25 to 45 years of age.a

Nystagmus is found chiefly in miners who work at the coal face in a more or less constrained position of the body and the eyes. The methods of mining in England differ somewhat from those in this country, especially in details that have an important bearing on the occurrence of nystagmus, and therefore it seems appropriate to include a brief abstract from the article of Snell regarding conditions under which nystagmus in English coal mines is most likely to occur. The abstract follows:

It is desirable to get coal in as large pieces as possible, and to do this they undercut or 'hole" the seam. A man sits with his legs crooked up, lying almost on his side, and strikes the coal with a horizontal swing of his pick at the bottom of the coal seam. He will cut away the coal to a height of 18 inches to 2 feet, and then as he gets deeper in he will draw his body under the coal, lying on one side or the other. The process is called "holing," and sometimes the undermining may be continued from 2 to 3 feet to as much as 7 or 8 feet; the distance varies considerably. As he proceeds with his work the miner applies timber supports to keep the coal from falling. This just described is called "bottom holing," but the seam may be attacked in the middle (middle holing) or at the top (top holing). A miner engaged at this work will direct his gaze to different parts as it becomes necessary for him to strike, for the eyes will follow the pick point, but the tendency will be for the gaze to be directed upward (using the ocular elevators) more or less obliquely. He will lie sometimes on one side and sometimes on the other. His legs will be crooked up, his head thrown back and flexed more or less on the shoulder beneath. * * Ninety-eight per cent of all cases of nystagmus coming under

*

my notice have been in men occupied at the coal face and more or less engaged at this kind of work.

a Snell, Simeon, Eye diseases and eye accidents in relation to industrial occupations, in "Dangerous Trades," by Thomas Oliver, London, 1902, chap. 58, pp. 761-762.

Snell, Simeon, Op. cit., pp. 762-763.

NYSTAGMUS A DISEASE OF COAL MINERS.

Regarding other underground occupations liable to nystagmus, the disease appears to be rare among them. Thus, for illustration, overseers whose work requires the inspection of underground conditions, both as regards freedom from gas and the security of the roof of the room or chamber in which the work is being done, suffer occasionally from nystagmus, according to Snell, probably because of the fact that their particular duties necessitate" the same upward and oblique direction of the gaze." He points out, however, in this connection that frequently the men employed as overseers have previously worked as coal miners, and he therefore concludes that, as a rule, all cases of nystagmus occur in those who are either working or have worked as coal miners, or who work in such positions as to require an upward direction of the eye for more or less prolonged periods. He also concludes that the causation of the affection "must be sought in this constrained position of the eyes by which chronic weariness is induced in the elevator muscles of the eyes. Like effects are found in other muscles of the miner, producing wry neck, tremors of the head, and quivering of the eyelids. It is thus similar to other occupational neuroses and in the same category as those found in writers, compositors, telegraphers, and many others."

BEARING OF INSUFFICIENT ILLUMINATION.

As regards the important question of insufficient or imperfect lighting, the opinion is expressed by Snella that nystagmus occurs among miners working with all kinds of lighting, and that he has met with it among those working with safety lamps, candles, large open lamps, as well as when the artificial light was really good. He concludes, however, that there are reasons "for believing that the strain is greater the worse the light, and that nystagmus is met with in greater frequency under such conditions." He quotes Nieden to the effect that 5 per cent of coal miners suffer from nystagmus, and he adds that his own observations support this view, but that in some places the percentage is higher. For illustration, among men working at a colliery with candles only, he found that 6 out of a total of 140 were absent from work on account of nystagmus, and that this represented only a part of those who, on examination, would have shown to have been actually affected with the disorder. Snell quotes Romiée, a Belgian authority, to the effect that the percentage of nystagmus cases was as high as 20, but he adds that this probably includes the less marked

cases.

a Snell, Simeon, Op. cit., p. 764.

Snell, Simeon, Op. cit., pp. 760-762.

PROGNOSIS, TREATMENT, AND CURE OF NYSTAGMUS.

The prognosis in nystagmus, according to Snell, is usually good, even for old-standing cases, if the directions as to a change of work are followed, and in such cases the nystagmus will usually disappear. As to treatment, particularly with reference to a change of occupation, Snell points out that—

In some cases it will suffice if the patient ceases from coal getting, without altogether stopping work in the mine, but generally it is advisable, especially if the nystagmus be of a high degree and of some standing, to recommend cessation altogether from work underground. After relief has been effected, return to the mine is practicable, provided the head can be kept straight and the upward turn of the eyes avoided. Resumption of the old kind of work is followed, sooner or later, by a recurrence of the symptoms. Medicinal treatment is also of service.

Finally, as regards the occurrence of nystagmus in other occupations than mining, Snell states that he observed the affliction, among others, in "compositors, metal roller, plate layer, plank cutter, saw maker, sanitary tube maker, fitter, iron founder, cage worker in a mine, glass manufacturer, youth in confectionery warehouse, and a man engaged in hanging up harness, and in another employed at the screens at the surface of a coal mine."

All of these instances, Snell points out, occurred under circumstances comparable to mine work, particularly as regards the strain upon the elevator muscles of the eyeball, on which, in his opinion, the degree of illumination had no effect. This conclusion, however, is not generally accepted.

FREQUENCY OF OCCURRENCE.

The first practical question is the probable number of miners affected with nystagmus. There are, unfortunately, no conclusive data on this subject, and the results of the only investigation that appears to have been made in this country—that is, in the State of Illinois-proved negative. According to the census of 1910 the number of men employed in coal mines in the United States was 613,519. If the proportion of miners affected with nystagmus were 5 per cent, the number of such cases in this country would be 30,676. In view of the paucity of references to nystagmus in American medical literature, it is extremely doubtful whether this proportion holds good for this country, as, seemingly, there have been few cases in American mines, although no thoroughly qualified opthalmic study has yet been made.

One of the most important contributions including American data was published some years ago by Nieden," of Bochum, the center of the coal-mining district of Rhenish Prussia. The study includes an examination of 7,500 miners. The pure rotatory form of nystagmus

a Snell, Simeon, Eye diseases and eye accidents in relation to industrial compensation, in "Dangerous Trades," by Thomas Oliver, London, 1902, pp. 760-762.

b Snell, Simeon, Loc. cit.

c Nieden, A., Der Nystagmus der Bergleute, Wiesbaden, 1894, 140 pp.

was found to occur in 72 per cent of the cases, the oscillating form in 12.5 per cent, and the mixed form in 15.5 per cent. Nieden questions the accuracy of Romiée's conclusion regarding a proportion of 20 per cent of nystagmus cases; and his own investigations made for the purpose of determining the facts, at least for the mining districts of Rhenish Prussia, were made with characteristic German thoroughness, and the existence of nystagmus in an acquired form was accurately determined in 299 cases out of a total of 7,416 miners, or 4.03 per cent.

On examination of 2,003 miners returning from work he found a proportion of 3.2 per cent suffering from nystagmus, whereas 1,913 men on commencing work were found to suffer in the proportion of 2.9 per cent. This result applies to a particular section and is, therefore, not strictly comparable with the total for the entire group examined, for which the combined percentage of nystagmus cases was 4.03. The difference as regards the occurrence of nystagmus on entry or exit can not be considered of great importance, but a more extended inquiry might disclose a more pronounced deviation from the normal.

Nieden adds an extremely interesting comparison of the frequency of nystagmus, based on his own examinations of miners and the results of his own private practice. Out of 3,017 miners requiring attention on account of eye troubles during a period of seven years, there were 172 cases of nystagmus, or 5.6 per cent. Against this proportion Nieden quotes 29,640 private cases of eye afflictions, out of which only 0.54 per cent were cases of nystagmus. In his opinion, therefore, the high proportion of 20 per cent as given by Romiée was not sustained by the experience in the Bochum mining district.

It is quite possible, however, that wide variations would be found to exist in different coal fields, for it is safe to maintain that the disease in the coal areas of the United States is relatively rare; in fact, Nieden points out that, according to his own investigations, most of the cases of nystagmus occurred among miners working in narrow seams, and that miners in some sections, where mining conditions were better, were practically free from the disease. Thus, for illustration, he determined that in the coal seams north of Bochum 7 per cent of the miners were afflicted with nystagmus, whereas in the coal seams south of Bochum only 0.25 per cent were affected. Upon further inquiry, however, he ascertained that in the northern coal seams the use of safety lamps was practically universal, whereas in the southern coal seams most of the men worked with open lamps and therefore under better conditions as regards illumination. He determined, by means of strictly scientific methods, that a miner using a Davy safety lamp during an eight-hour period worked under about onethird the amount of illumination normally provided by an open lamp.