Improper habits frequently induce this defect, while the eye and its muscles are perfect; for instance, m children, who accustom themselves to view different things at one time; or, who are placed obliquely towards any object that may attract their attention. Another cause is mal-conformation of the retina, or such parts as serve to convey impressions to the point of vision; so that persons, thus situated, are obliged to turn the eye from the object to be investigated, in order that they may be enabled to behold it more distinctly. - Farther, it often proceeds from weakness, or defect of either eye, so that both cannot be mutually employed. Besides, it may be consequent on affections of the brain, epilepsy, terror, and defluxions of rheumatic humours.
The method of cure to be adopted in this unpleasant distortion, varies according to the cause. Thus, in children, and in cases of weakness of the eyes, it may be remedied by mechanical contrivances. Hence, when there is no organic defect in either eye, which is frequently the case with persons who squint from a depraved habit of moving their eyes, the disease may often be cured. Dr. Darwin remarks (Philosophical Transactions, vol. 68), that in all the squinting people he had occasion to attend, one eye was less perfect than the other : these patients are, in his opinion, certainly curable, by covering the best eye many hours in the day; as, by a more frequent use of the weak eye, it not only acquires a habit of turning to the objects which the patient wishes to see, but gains at the same time, a more distinct vision : in both these respects, the better eye is under some disadvantage, which also facilitates the cure. This ingenious physician relates, in the same paper, a remarkable case of a boy, then five years old (now a reputable English clergyman at Edinburgh), who has the misfortune of viewing every object with one eye only at a time. Dr. D. directed a paper gnomon to be male, and affixed to a cap; and, when this artificial nose was placed over the patient's real nose, so as to an inch a his eyes, the child, rather than turn his head so far to look at oblique objects, immediately began to exert the eye winch was nearest to them. But, having the misfortune to lose his father, soon after this method was begun to be followed, the child was neg-letted for six years, during which time the habit was confirmed in such a manner as seemed to leave little room to hope for a cure. Dr. D. however, being again called, attempted a second time to remove the deformity, by a similar contrivance. A gnomon of thin buss was made, to stand over his nose, with a half-circle of the same metal to go round his temples: these were covered with black silk; and, by means of a buckle behind bis head, and a cross-piece over the crown of his head, this gnomon was worn without any inconvenience, and projected before about two inches and a half. By the use of this machine, he soon found it less inconvenient to View all oblique objects; with the next to them, instead of the eye opposite to them.
After th:s habit was weakened, by a week's use of the gnomon, two bits of wood, about the size of a goose-quill, were blackened all but a quarter of an inch at their summits; these were frequently presented to him to look at; one being held on one side the extremity of his black gnomon, and the other on the opposite. In viewing these, they were gradually brought forward beyond the gnomon, and then one was consqU cealed behind the other : by such means, in anothcr week, he could bend both his eyes on the same object for half a minute together; and by continuing the use of the same machine, he was in a fair way of being cured.
Lastly, if squinting arise from any adventitious circumstance, such as tenor, defluxions of humours, etc. the removal of those causes will also cure the disorder-, but, re it originates from mal-conformation of the organs of vision, or has been so long neglected as to become confirmed, it is not in the power of art to afford any re