NATURE 



385 



THURSDAY, FEBRUARY 21, i! 



THE ILLUSTRATED OPTICAL MANUAL. 

 The Illustrated Optical Manual. By Sir T. Longmore, 

 C.B., F.R.C.S. Fourth Edition. Pp. 239. (London : 

 Longmans, Green, and Co., 1888.) 



IN the present edition this manual, which was origin- 

 ally intended for army medical officers, has been 

 considerably enlarged, with a view to its suitability as a 

 text-book for civil as well as for military surgeons. Civil 

 surgeons, however, are abundantly supplied with excel- 

 lent works on ophthalmology ; and for this reason (to say 

 nothing of the fragmentary nature of Sir T. Longmore's 

 Manual) we scarcely think that it will ever enjoy any 

 large vogue amongst that class. The author treats of the 

 detection and correction of refractive errors, and of 

 optical defects generally : surely it would have been 

 better to produce at once a complete manual of ophthal- 

 mology than to treat the subject in this piecemeal fashion. 

 For how can any military surgeon be certain of his 

 diagnosis in a case unless he has a thorough knowledge, 

 not only of errors of refraction, but of eye diseases as 

 well ? 



The opening chapter, on optical principles, is very 

 good ; the description of refraction, &c., being well and 

 clearly done. Speaking of the composition of spectacle 

 lenses, the author points out that the only real advantage 

 possessed by quartz lenses ("pebbles") over ordinary 

 crown glass ones is that they are harder, and, therefore, 

 are not so easily scratched. By experiment, he has ascer- 

 tained, contrary to the common supposition, that there is 

 no difference in weight between pebbles and crown glass 

 lenses of corresponding powers. The tourmaline forceps, 

 for determining whether a pebble lens is, or (as is often 

 the case) is not, cut exactly perpendicular to the axis of 

 the crystal, is figured and explained. 



We notice some peculiar statements in the chapters on 

 myopia, hypermetropia, and astigmatism. For example, 

 it is stated that the myopic eye " usually presents some 

 peculiar characters indicative of its condition. It is pro- 

 minent, or even appears to protrude ; the pupil is usually 

 contracted." At times, no doubt, cases of high myopia 

 are seen in which the eyes do appear to be unduly 

 prominent ; but it is a sign of no value, and one which is 

 more often absent than present. The pupil, if it shows 

 any change at all, tends, in myopes, not to contraction, 

 but to dilatation. In estimating refraction by the direct 

 method, the examiner is recommended to place himself 

 18 inches or more from the patient's eye. This is an 

 extraordinary statement, our impression heretofore being 

 that it was impossible to be too close to the patient's eye. 

 In examining the fundus oculi by the direct method 

 of ophthalmoscopic examination, the examiner, it is 

 stated, will have little or no tendency to bring his ac- 

 commodation into play. This, again, is quite contrary 

 to the experience of most persons ; in fact, one of the 

 greatest troubles experienced by tyros is that they almost 

 invariably call their accommodation into play when it 

 should be quiescent, and many adepts are unable, even 

 after years of practice, completely to relax their cihary 

 Vol, XXXIX. — No. 1008. 



muscles. The refraction, as tested by the direct method, 

 is enjoined to be taken at the optic disk. Although this 

 is the usual plan, a caution might well have been given 

 that the refraction at the blind spot (optic disk) and at the 

 yellow spot (the point of the most accurate vision) may 

 differ appreciably. Again, in practising retinoscopy, it is 

 recommended that the patient's eye be turned inwards. 

 By this means, doubtless, a more easily seen reflex is 

 obtainable with a small pupil, but this great drawback 

 attaches to the method, that the refraction of some part 

 of the fundus, other than the yellow spot, is estimated. 



Sir Thomas Longmore gives currency to the views of 

 his colleague. Dr. Macdonald, on the subject of normal 

 astigmatism. Briefly, they are as follows. Every eye 

 has a greater curvature in its vertical than in its horizon- 

 tal meridian, but the difference in curvature is so slight 

 that it does not interfere with visual acuteness. The 

 meridian of greater curvature is not exactly vertical, but 

 intersects the vertical meridian at an angle of about 15°. 

 When a vertical line is held within the near point of an 

 eye it is blurred ; but when the left eye alone is used, the 

 left side of the line is less blurred than the right side ; when 

 the right eye alone is used, the right side of the hne is seen 

 more distinctly than its left side. The effect of this is 

 that a line held within the near point is seen more 

 distinctly when both eyes are used than when either eye by 

 itself is used. Hence, in this view, normal astigmatism 

 becomes an important aid to the perfection of binocular 

 vision of near objects. 



The regulations as to the visual examination of recruits 

 are given in detail. The vision of regular army recruits 

 is ascertained by their ability to count test-dots, one-fifth 

 of an inch in diameter, held 10 feet from the eye : this 

 is equivalent to a bull's eye target, 3 feet in diameter, 

 at 600 yards. Sir Thomas remarks that the standard is 

 very low, since an eye with normal vision should be able 

 to count the dots, not at 10 feet, but at 43 feet. At present, 

 therefore, recruits may be accepted who possess less than 

 one-fourth normal vision. 



There is no regulation in the English army allowing 

 ametropic soldiers to wear correcting glasses. Sir Thomas 

 Longmore states that the only disadvantage accompany- 

 ing such permission would be the difficulty of replacing 

 broken lenses when their wearers were on foreign service. 

 The German soldiers, in 1870-71, wore spectacles ; and^ 

 since then, their use has been sanctioned in the French 

 army. Perhaps when the British mind is emancipated 

 from the thraldom of the red coat, it may give its soldiers 

 fairer play with respect to the use of spectacles. Some 

 day a regimental optician may accompany soldiers on 

 foreign service. 



Malingering, or feigned blindness, is stated to be rare 

 in our army, although sufficiently common in the armies 

 of those countries where conscription is in force. If we 

 are to take the two illustrative cases as samples, the British 

 Tommy Atkins does not appear to be so good at deception 

 as he is at fighting. One of the cases is reminiscent of a 

 half-forgotten anecdote. A soldier complained that his 

 sight was very defective. The surgeons were unable to 

 prove that he was shamming. One day he was suddenly 

 ordered by a sergeant to pick up a pin from the floor, 

 where it had been placed at some distance from him ; 

 and, taken unawares, he did so. As the text somewhat 



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