20 THE OPTICAL DEFECTS OF THE EYE. 



which are so apt to occur in short-sighted persons, are undoubtedly 

 greatly promoted. Tor this reason, we should always tell these 

 patients to read with their head well thrown back, and to write at a 

 sloping desk. Bat it may, on the other hand, be urged that it is 

 just in looking at near objects that myopic persons have an advan- 

 tage, for they can see them remarkably distinctly. And the great 

 danger is, that after reading for a short time with spectacles, the 

 patient, on getting somewhat fatigued will, instead of laying the book 

 aside, approach it nearer to the eye, in order to gain greater retinal 

 images, and thus strain and tax his power of accommodation too 

 much. If we, for instance, give a patient whose far point lies at 8 

 inches, a pair of spectacles which enable him to read at 12 inches, he 

 will, if not very careful, after a short time almost insensibly bring 

 the book nearer to his eyes, and thus have to make use of a greater 

 amount of accommodation. If he does this frequently, he will soon 

 increase his myopia. The greater the range of accommodation the 

 less harm will spectacles do, and vice versa. Spectacles may also be 

 used for near objects in those cases of myopia in which asthenopia 

 (depending upon insufficiency of the internal recti muscles) shows 

 itself as soon as the patient has read or worked at near objects for a 

 short time. "Whilst these forms of myopia may be furnished with 

 spectacles for near objects, it is very dangerous to permit .their use 

 in patients whose range of- accommodation is very limited, and who, 

 moreover, suffer perhaps from such an amount of amblyopia (gene^ 

 rally depending upon sclerotico — choroiditis posterior) that they 

 cannot read No. 4 or 5 Jager even with the most accurately chosen 

 glasses. Such patients will bring the object very close to the eye, 

 in order to obtain large retinal images, the accommodation will be 

 greatly strained, the intra-ocular tension be increased, and great 

 mischief will be sure to ensue. If there is much amblyopia, specta- 

 cles should not be permitted at all for near objects."* 



In cases where the myopia is extreme, there usually co-exists pos- 

 terior staphyloma of the sclerotic. Von Grrsefe says it is present in 

 all cases of myopia where the "far" point is less than five inches; 

 the myopia being less than \. Out of sixty cases of myopia exam- 

 ined by J. Z. Laurence, forty-four had posterior staphyloma. 



The presence of this disease can be easily diagnosed with the 

 ophthalmoscope. (See Hulke or Zander on the ophthalmoscope.) 



•Mr. J. Z. Laurence, of London, recommends that deeply concave lenses be tinted, in 

 order to obviate their " dazzling " effect.— (Med. Times and Gazette, Oct. 22ad, 1864.) 



