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be fully equal to the requirements of the general practitioner, but which does not include glasses unnecessary except after cataract operations or in rare cases, the author has devised a case which he believes fully meets the requirements.

The object is attained by including in a single set of lenses all those numbers more commonly in use. All the numbers of spherical lenses contained in Nachet's large case up to 10. D (old No. 4), are retained, with such other glasses as are best calculated to produce all the higher denominations with the least trouble. By combining not more than two lenses at one time, all the numbers of the best trial cases may be readily obtained. A similar arrangement holds in regard to cylindrical lenses. Numbers frequently required correspond to those of the most complete trial cases, while all the others can be obtained with perfect ease by simple combinations.

The lenses are constructed upon the metrical system; hence, combinations can be made without any complex mathematical calculations.

The case also contains a set of prismatic glasses, opaque and stenopaic disks, plain and colored glasses, and an adjustable trial-frame. With this trial case, all the examinations in regard to refractive conditions or muscular anomalies can be made as conveniently as with the most complete and expensive case.

If the examiner, being provided with suitable trialglasses, wishes to ascertain the refractive condition of the eye to be examined, he excludes the other eye from the act of vision by placing in his trial-frame an opaque

disk, or by any suitable device. The person examined is now requested to read the letters of the trial-card, and the extent to which the letters are seen is noted. If the letters of No. XX are read at twenty feet, we conclude that myopia does not exist, and we are to determine the presence or absence of hyperopia or a moderate degree of astigmatism. The myopic vision is unable to adjust by accommodation for a distant point, but one in whom the faculty of accommodation is active may conceal a low degree of astigmatism or a high degree of hyperopia. If the patient sees as well with a convex glass of any denomination, as without, manifest hyperopia, equal to the strongest glass thus accepted is proved. But let us suppose that the type of No. XXX is read, and that No. XX can not be clearly made out. Vision is then 38, and if no disease or obstruction exists it may be hoped that vision can be raised to. First, a very weak convex spherical glass (50 D) is placed before the eye; if vision is somewhat improved, a stronger and stronger may be tried, until the best results are attained. But, before the eye becomes fatigued, the effect of a weak convex cylindrical glass should be compared with that of the spherical. The cylindrical glass should be placed in various positions before it is rejected. If the convex spherical aids vision and the cylinder does not, to an equal extent, simple hyperopia is to be assumed. In case neither the convex spherical nor cylindrical lens aids vision, but rather renders the characters indistinct, concave spherical and then cylindrical glasses are to be tried in the same manner.

In case neither assists the eye, we

are to assume that no refractive error exists, unless, with the ophthalmoscope, we are able to discover the refractive anomaly. We have emmetropia with but vision.

If the eye subjected to examination is hyperopic, and is fully under the influence of atropine, the absolute hyperopia may be discovered; otherwise, we can determine only the manifest refractive error.

The strongest glass which is found to give additional sharpness of detail to the letters represents the degree of manifest or absolute hyperopia, as the case may be. It is not to be forgotten that when atropine or some other mydriatic is not used, a certain amount of hyperopia may remain latent; that the sum of the manifest and latent hyperopia equals the total. Hyperopia which may be latent at one time may become manifest at another. Hence the glass which appears to correct the manifest refractive error at one time may be found at a later time to be too weak.

If a convex glass of 100 D corrects the absolute hyperopia, then H = 1·00 D ; but if it is only the manifest hyperopia of an eye which may, under the circumstances, exercise its accommodation, H m = 1.00 D.

The question of the extent to which glasses should be used in hyperopia is an important one.

Theoretically, the accommodation should be relieved from all but the amount of exercise which would be required in emmetropria, but practically it is found more convenient, in many instances, to allow the eye to subject itself to a certain amount of accommodative effort at a distance.

Children with moderate hyperopia need not, as a general rule, use glasses for distance. But if an insufficiency of some of the ocular muscles exists, there may be an advantage in their use even for distance. If the child suffers from nervous complications, such, for instance, as chorea or headaches, it may also be advisable to employ the glasses habitually. In other cases a glass of rather less strength than corrects the absolute hyperopia is to be used for near work. In high grades of hyperopia, or in case of loss of accommodation from age or other cause, the hyperopia should be corrected for all distances.

After the age of forty-five or fifty, most hyperopic persons will require two pairs of glasses: one for correcting the hyperopia, to be used for the distance; the other stronger, neutralizing both the hyperopia and presbyopia.

Let us suppose that, in the case already assumed, a convex glass does not improve but rather dulls vision at the distance of twenty feet, and that a concave glass serves to render the letters of the trial-card more distinct. Myopia is to be assumed, and the weakest concave glass giving the most distinct vision at twenty feet, the accommodation being relaxed, represents the degree of myopia. In determining the degree of myopia, we begin by selecting a glass of low and gradually of higher power, until the lens affording the greatest improvement in vision is found. We may form an approximate conclusion in respect to the degree of myopia by finding the greatest distance at which ordinary print can be read. We estimate the distance at which

the page becomes indistinct, which indicates the far point of vision. If this is less than the distance at which the same page would be read by the emmetropic eye, myopia is presumed.

If the distant point for reading the type No. 50 be one fourth of a metre (about ten inches), we have, approximately, myopia 4·00 D, or. We may now try the effect of a negative glass of 4·00 D (of the old system No. 10), generally with the effect of enabling the letters to be carried to the distance of half a metre, and of materially improving vision at the distance of twenty feet. We now seek for the weakest glass that will enable the patient to see well. It is not to be forgotten that the strongest convex glass with which the patient can see well at a distance, and the weakest concave glass with which vision is not less acute than with. those of stronger power, represent respectively the manifest hyperopia and the grade of myopia.

If, now, in the case above supposed, we can obtain a slight increase of vision, or even equal vision, by placing in front of the 4:00 D lens a weak convex glass, say of +50, our correcting glass is too strong, and must be reduced to the extent of the value of the second glass. On the contrary, if a weak concave glass assists, we must increase the strength of the original glass in a corresponding degree.

In practice, the subject of myopia should always use the full correcting glasses for distant seeing, but this may be less convenient for near work. The accommodation is often enfeebled in myopia, and the effort at adjustment for near points, such as would be

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