8o Orbit 



keeping the head in such a position that there is no work for the 

 inferior oblique to do ; thus he keeps the head tilted upwards and 

 outwards. 



When the superior oblique is paralysed there is deficient abduction 

 and depression of the cornea, so the head is turned to that side and is 

 kept somewhat depressed. 



Rule. To enable the practitioner to detect the exact muscular 

 paralysis by merely looking at the patient's face, Dr. Ranney has 

 given this formula : ' The head is so deflected that the chin is carried 

 in a direction corresponding to the action of the affected muscle.' 



Strabismus (squint) is that condition in which the visual axes are 

 not parallel. One eye or both eyes may be at fault. The commonest 

 form is that in which the axes are directed towards the nose con- 

 vergent squint, 



Upon the retina of the eye which deviates inwards the object falls 

 to the inner side of the yellow spot, and double vision is produced, 

 which, however, the person is able to educate himself to disregard. 



To detect the squinting eye, the tip of the finger is held about 

 eighteen inches in front of the eyes. One eye promptly fixes on to it ; 

 the other wanders. Then a piece of ground glass is placed in front of 

 the eye which watched the object, and the wandering eye after some 

 hesitation becomes directed on the object. Then, on the observer 

 looking through the dull glass, the original working eye is found adrift. 



As a rule, the subject of convergent strabismus has that congenital 

 defect a shortness, it may be of the eye- ball by which rays are not 

 brought to a focus until they have passed beyond the yellow spot. 

 Therefore his ciliary muscle has to struggle in a forced effort at ac- 

 commodation, so that the rays may be duly focussed. But accommo- 

 dation is closely associated with convergence (p. 58), and so the child in 

 due course has his eye-balls adducted. Thus the frequent occurrence 

 of convergent strabismus is fully accounted for. 



With double convergent squint the object must fall to the inner 

 side of the yellow spot in both eyes, but the child acquires the art of 

 moving his head and arranging his eye-balls so that he can depend on 

 the image falling correctly on one eye which, in due time, becomes 

 the ' working eye ' ; moreover, he at last takes no notice of the image 

 in the other eye. Thus, he is believed to squint with one eye only. 

 If the 'working eye' be covered, and he focus the object with the 

 ' wandering eye,' which he can quite well do, and the ' working eye ' be 

 then uncovered, it is found to squint ; but it promptly turns on to the 

 object, as is its custom, and allows the other eye to get adrift again. 



The treatment of convergent squint. If the deviation be caused by 

 hypermetropia (p. 86) it will yield in due course to convex glasses. But if 

 the defect be permanent, subconjunctival tenotomy of the internal rectus 

 or recti is demanded. 



The operation. The lids having been fixed apart by the speculum, 



