PHYSIOLOGY 



Certain complications sometimes attend myopia ; these are divergent strabismus' 

 eye-strain, and spasm of the accommodation. 



The divergent strabismus has a similar origin to the convergent strabismus met 

 with in hypermetropia, namely association of deviation of the eye axes with the adjust- 

 ment of the accommodation. Now since in the normal individual the relaxation of the 



accommodation of the eye is associated 

 with parallel axes of the eyes (in order 

 to look at distant objects), in myopia 

 the disuse of the accommodation for 

 near vision causes the eye axes to re- 

 main straight and therefore produces 

 the effects of an external strabismus. 

 The use of glasses introduces again the 

 necessity of accommodation, exactly as 

 if the eye was normal, and therefore 

 abolishes the strabismus. In the ma- 

 jority of cases an actual strabismus 

 does not develop, but there is never- 

 theless a strong tendency to diplnpia. 

 especially when the eyes are tired. 

 The eye-strain which frequently ac- 

 companies myopia probably has its 

 origin in the effort to converge the 

 eye axes without at the same time 

 calling the accommodation into play. 

 Spasm of accommodation fre- 

 quently accompanies myopia, and has 

 the effect of making the myopia seem 

 greater than it actually is. The true 

 state of affairs is at once found when atropine is used, because the accommodation is 

 thus .abolished. Sometimes in children spasm of accommodation occurs without any 

 actual abnormality of refraction. Such cases should be treated with the same care 

 as those that are already developing myopia. 



ASTIGMATISM. The condition of the eye called astigmatism is one in which 

 parallel rays are not brought to a focus in a single plane, but in a number of difYerent 

 planes. There are two different varieties of astigmatism. In the first or irregular 

 variety the separate parts of one meridian of the eye form different foci. 

 This is found to occur during the development of cataract in the crystalline 

 i ud also after ulceration of the cornea. The effects of this form of astigmatism 

 II \ i>ion vary with the severity of the condition ; in moderate cases a frequent pheno- 

 menon is the formal inn of a double image in the affected eye. <J lasses as a rule do not 

 give Umeh't. In severe types the use of, a stenopaeic aperture may improve definition. 

 In the second variety, or regular astigmatism, the parts of any one incri 

 dian give the same focus, but the different meridians have different foei. 

 Tin -re arc however two meridians at right angles to one another, one of 

 which has the longest and the other the shortest focus, the meridians 

 in between showing an orderly sequence between these two extreme values. 

 Thus the use of the term regular astigmatism. Two types of patient are found to 

 suffer from this condition, those who have inherited and those who have acquired it 

 .picnce to injury, operation or disease. The effects on vision are varied, but 

 the ch iracteristie features arc distortion of objects looked at. and indistinctness of 

 lines ii! one direction, u hile those at right angles arc quite sharp. Headaches, eye strain 

 and dimness of vision an- \ CIA common. Many t vpcs are nn-t \\ it h because 1 he m.i \irnum 

 and minimum meridian may occupy any angle so long as they are at right angli- t" 

 one another, and they may have any degree of myopia or hypermetropia. 



Fio. 269. The asymmetry of the eyeball 

 and kinking of the optic nerve caused by 

 high myopia. 



