VOL. LXXXVII.] PHILOSOPHICAL TRANSACTIONS. 81 



object, while a blind one in its motions follows the other, is probably, that the 

 indistinct vision of the imperfect eye prevents the muscles from directing it to the 

 object with the same accuracy as those of the other do ; this small deviation from 

 the axis of vision renders the object double, and interferes with the vision of the 

 perfect eye ; and it is in the effort to get rid of the confused image that the mus- 

 cles acquire a habit of neglecting to use the imperfect eye. It may also happen, 

 when the eye is so imperfect as not to receive a correct image of any object, that 

 it may have been neglected from the beginning. Distinct vision being at once 

 obtained by the perfect eye, the end is answered, and the mind is never afterwards 

 led to employ the other. The direction the eye takes under either of these cir- 

 cumstances is inwards, towards the nose, the adductor muscle being stronger and 

 shorter, and its course more in a straight line, than any of the other muscles of the 

 eye. That the eye, when not accurately directed to the object, produces confused 

 vision, and is for that reason turned away, appears to be confirmed by the case of 

 a patient, from whom I had extracted the crystalline lens. This man, at first, saw 

 objects double, in a manner which extremely distressed him ; but after some 

 months he acquired the habit of neglecting to employ the imperfect eye, and no 

 longer found any inconvenience. 



The different degrees of squinting appear to be in proportion to the imperfection 

 in the vision of the eye, and, in some instances, the person is capable of seeing 

 distant objects with both eyes, and only squints when looking at near ones. The 

 following case is of this kind. A young lady, 23 years of age, has been observed 

 to squint from her infancy ; this has not been considered by her friends as the 

 consequence of any defect in her eyes, but as arising from the cradle in which she 

 lay having been so situated, with respect to the light, as to attract her notice in 

 one particular direction, so much as to occasion a cast in one eye. Her eyes are 

 apparently both perfect ; when she looks with attention at an object some yards 

 distant she has no squint, but if her eyes are not engaged by any object, or a very 

 near one, she squints to a considerable degree. On being asked if she saw objects 

 distinctly with both eyes, she said certainly, but that one was stronger than the 

 other. To ascertain the truth of this, I covered the strong eye and gave her a 

 book to read; to her astonishment, she found she could not distinguish a letter, or 

 any other near object. More distant objects she could see, but not distinctly. 

 When she looked at a bunch of small keys in the door of a book-case, about 12 

 feet from her, she could see the bunch of keys, but could not tell how many 

 there were. 



To see how far the 2 eyes had the same focus, she was desired to look at an ob- 

 ject in the field of a microscope; and it was found that she saw most distinctly 

 with both eyes at the same focal distance, though the object was considerably more 

 distinct to the perfect eye than to the other; so that the focuses of the 2 eyes were 

 the same. I desired her to cover the perfect eye, and endeavour to acquire an 

 adjustment of the other to near objects, by practising the use of that alone. At 



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