Those cases where it is a question of uniting homonymous double images are very instructive when considering tenotomy. Only when squint arises after childhood (after the fifteenth year) does it cause troublesome diplopia, this accords naturally with the laws of normal binocular fusion learnt meanwhile. (On the other hand those cases, which sometimes occur after tenotomy, with the double images in a position which does not correspond to the normal physiological laws and which cannot therefore be united by prisms, are naturally unsuitable for the operative removal of diplopia.) Cases in which convergent squint is followed by troublesome double images, appear, with the exception of the hysterical form mentioned on p. 41, chiefly in myopia, more seldom in emmetropia, and very rarely in hypermetropia; for if the conditions contained in the ocular muscles are coincident with hypermetropia, squint usually arises in the course of childhood, before normal binocular vision has become a fixed habit. As the cases here under consideration are not very common, I will relate a few from which conclusions may be derived as to the effect of tenotomy. CASE 45.--Miss von B--, æt. 14, came under treatment on May 1st, 1875, for diplopia, which made its appearance about a year previously. Emmetropia and full visual acuteness exist on both sides. The double images are homonymous and further apart on both sides of the visual field. At first single vision existed only to about 0·75 m.; gradually, however, the area of single vision was extended by practice of the outward movement, supported by the use of prismatic spectacles, so that after a year patient could see singly to a great distance. This improvement was not maintained. At the beginning of 1879, diplopia was again present to a troublesome degree, particularly on looking downwards; on looking straight forwards the left eye showed a slight convergent deviation, amounting at most to 2 mm. During various examinations the distance of the double images was stated to be now less, now greater, a prism of at least 5°, at most of 9°, was requisite for correction. Diplopia was at once removed by tenotomy of the left internal rectus, with very slight loosening of the conjunctiva, and has not appeared since.