letters of a page, which at first appear clear, after a short time run together, and it becomes necessary to discontinue the work while the accommodation is relieved. Pressing the eyes with the hand, when this sense of fatigue is experienced, is a common and characteristic means of relief. If the act of accommodation is persisted in after these warnings, severe pain in and about the brow and at the back of the head, general discomfort, and nausea, may follow. As a result of frequent straining of the muscles of accommodation, hyperopic persons often have redness of the conjunctiva and of the borders of the lids. The more general and distant reactions have been shown in the first part of this work.

In the higher degrees of hyperopia visual acuity is often diminished, so that even with correcting glasses the visual power is considerably less than the standard.

Donders, to whom we owe the knowledge of the relations of these symptoms of fatigue to hyperopia, divides the condition into latent and manifest hyperopia.

In latent hyperopia the patient unconsciously uses his accommodation, and thus conceals a part or the whole of the refractive error. This is especially the case with young persons, in whom the power of accommodation is active, if the degree of hyperopia is only moderate; but even a high degree of hyperopia may be associated with a vigor of accommodation sufficient to conceal it. As age advances, however, there comes a time when the lens being less elastic than in earlier

life, the accommodation no longer suffices to render even distant objects clear, and still less to enable the patient to read.

The hyperopia is now manifest in part at least. A suitable glass may raise distant vision to the normal standard and the same glass may enable the subject to read.

To ascertain the absolute amount of hyperopia, it is necessary, especially in all young persons, to render the latent hyperopia manifest, which can be accomplished if we suspend the action of the ciliary muscle by atropia or other drugs producing similar effects.

MYOPIA, OR NEAR-SIGHT (M).

Myopia is the condition opposite to hyperopia. The axis of the eye being usually too long instead of too short, as in hyperopia, parallel rays are brought to a focus in front of the retina, and, before reaching it, cross and fall upon it in circles of diffusion (Fig. 7).

Hence, rays must be divergent as they enter the eye in order to meet at the retina. The far point of vision, then, for a myopic eye, instead of being at infinite distance, is brought nearer, and a myopic eye is consequently a near-sighted eye. The distance of the remote point of distant vision will depend upon the amount of elongation of the eye. If this be slight, there will be a correspondingly slight degree of myopia, or near-sight. If, on the contrary, the elongation be great, there will exist an excessive degree of nearsight.

Myopia, when dependent upon anatomical forma

tion, is scarcely modified for the better by treatment, but unless suitable precautions are used there is a strong progressive tendency. Cases of slight myopia, if neglected, are liable to develop rapidly into high degrees of near-sight. It is important, therefore, that the first indication of near-sight in children should receive the most careful attention. The popular prejudice which existed formerly that near-sight diminishes with age is erroneous, and should never be an excuse for relaxing the most vigorous attention to even the slightest degree of myopia. A slight change in the length of the eyeball after the age of fifty is, in this connection, a matter of technical rather than of practical interest. My own observations have convinced me that myopia is very frequently, if not in general, one of the results of anomalies of the ocular muscles, and that the condition most conducive to myopia is that in which the visual line of one eye tends in a higher direction than that of the other.

In low degrees of myopia the defect may escape observation, as objects within certain distances are clearly seen, and the fact that objects beyond this point are not well seen is not regarded by the patient as in any way peculiar. Indeed, people with moderately high degrees of near-sight often become aware of their defect for the first time by accidentally putting on concave glasses, which reveal to them objects at a distance in a manner to them surprisingly clear. Usually, however, it will be observed that the myope holds a book or work nearer than the usual distance, and fails to recognize distant objects as well as other

people. In low or moderate degrees, glasses are not required for reading or writing, but in higher degrees work must be brought very near to the eyes in order to obtain distinct images, and in these cases concave glasses enable the myope to carry the book or other work to the ordinary distance. In near-sight, if of only moderate degree, the accommodation is commonly used in reading and the book is brought near the eyes; but, as age advances, the eye becomes presbyopic in the same manner as in emmetropia. The near point recedes toward the distant point, and thus, while the subject of myopia can see at no greater distance than before, there is a necessity for removing objects for near view toward the distant point. The slight change in the refractive condition which has been alluded to above, must not be considered here. The range of vision, then, is less extensive, but the near-sight remains. It was upon the facts that the book is held at greater distance, or that the glass for near-sight must be left off while reading, that the popular error that near-sight decreases with age was founded.

Examining the history of near-sight in an individual, it will, in the majority of instances, be found that until the age of from ten to fifteen years, vision for distance was good, but that near-sight, then appearing, developed rapidly. In a certain proportion of instances, however, myopia is developed at a very early period of life, and in a very small proportion of cases it may be congenital.

The subjects of near-sight often suffer from redness

of the eyes and eyelids, from pain in the brows and general headaches, from intolerance of light, and from the presence of motes in the field of vision,

Near-sighted eyes are commonly diseased eyes. The rapid elongation of the eyeball is often associated with disease of the choroid, and in some instances with separation of the retina from the choroid. A condition called posterior staphyloma, in which the sclerotic is distended backward, is often developed in myopia. The principal changes, as described by Donders, are "atrophy of the choroidea on the outside of the optic nerve, when myopia is highly developed, combined with change of form of the nerve-surface, a straightened course of the vessels of the retina, incomplete diffuse atrophy of the choroidea in other places, and morbid changes in the yellow spot." These changes can be readily recognized by the aid of the ophthalmoscope. Fig. 8 shows the irreg ular, white crescent which marks the atrophy of the choroid.

Besides the elongation of the axis of the eye, myopia may be the manifestation of the increased index of refrac

FIG. 8.

tion of the dioptric media or of excessive curvature, as in conical cornea.

A condition of involuntary and excessive contraction of the ciliary muscles (spasm of the accommoda