The light-sense in strabismus, especially in the amblyopia of strabismus, examined by means of a new photometer
Mackay, Duncan Matheson
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One is now in a position to draw conclusions. I have put together all the cases of convergent strabismus with amblyopia, examined as to the light -sense either with or without glasses, which show a marked difference in their light-sense (groups 1 and 9).That is, of 15 cased (Divisions 1 and 2), in which the L.M. is affected markedly, 9 have it increased, and 6 have it diminished.On the other hand, of 20 cases (divisions 1 and 3), in which the L.D. is similarly affected, 15 have it increased, and 5 have it diminished.In like manner I put together those cases of convergent strabismus, without amblyopia, in which there was a marked difference in the light -sense of the two eyes. (Tables 14 and 37).Here then, of 7, which have a variation in the L.M., in 3 the L.M. is greater, and in 4 less. Of 6 which vary as to the L.D., in all the L.D. is increased.In the next place, I have made a similar summary of the cases of divergent strabismus, with amblyopia, which, with or without glasses, show a marked difference in the light-sense of the two eyes (Tables 21 and 42).That is, where the L. M. is affected- markedly, in 3 out of 4 it is increased, and in 1 diminished.Where the L.D. is markedly affected, out of 5 cases it is increased in 3, and diminished in 2.So far as it goes, this table points to defect in the L.T.C., and also, though in less degree, to defect in the L.P., but the number of cases is too small to permit of useful generalisation.Also, the number of cases of divergent strabismus without amblyopia (Group. 7.) is too small to be worth considering.Lastly, I may recall the fact (p.48) that, in amblyopic eyes without strabismus, there is no overwhelming evidence pointing either to the L.M. or the L.D., though either may be affected.This inquiry then has a negative result, for no abso- lute rule as to the light -sense in squinting or amblyó_ is eyes, as compared with the et in their normal fellows, has been revealed. In all the groups, a large proportion of the cases present equal or nearly equal light -sense in the two eyes. Of the remainder, some have defective L.7., and some defective L.D., some have more acute L.M. and some more acute L.D. And neither acutt: of vision, age, nor refractive error, seems to assist in determining any classification of each kind. Of those cases of Convergent Strabismus however, either with or without amblyopia, in which the light- sense is markedly different in the squint- ing eye from that in the normal eye, the majority show a defective L.D. In other words, these cases seem to have some affection of the optic nerve or nervous elements of the retina.One is forced to the conclusion, therefore, that probably the light -sense is not primarily responsibe for the squint or for the amblyopia. The explanation of squint is still hidden.PHOTOMETRY OF NORMAL EYES:- In order that I might report on the cases cf toxic amblyopia, which I have examined the light -sense of, it is necessary to determine the average of the normal eyes, as to their L.M. and L.D.In doing this, I have included all the eyes of the preceding study, which did not squint, and a few extra ones which were seen during the same time.All were perfectly healthy, as evidenced by the ophthalmoscope and the visual acuity. I have accordingly made tables of 73 eyes,whose light -sense was examined while they wore the correcting glasses necessary, and of 29 eyes which were examined naked. I have tabulated each lot in accordance with their decades of life, having sub- tables of the different acuities of vision under each decade.The figure in the third column is the area of the circular ring formed by the partly opened diaphragm and the central cylinder of wood. That in the fourth column is the proportion expressed as a decimal fraction, of the extra area, needed to enable the observer to note a difference in the brilliancy of the discs, to the L.M. The figure in the fifth column is the diameter of the diaphragmatic aperture at the first reading, and that in the sixth column is the diameter at the second reading (p.16)The form-sense is that obtained by correcting the refractive error with glasses, which were removed before introduction to the photometer.These two tables collected into one, ,under the decades of age, give a result as follows:These, again collected together under the decades, give the following figures as the averages for the five decades named, and they are seen to be all similar;We can now reckon the cases of Tobacco amblyopia, of which I have 12 eyes to report on.3 of these eyes have distinct increase in the L M. one of 6 them seeing Ja, and two 6/36.3 have markedly increased L.D. one seeing 6/6-0, one of them seeing 6/36, and one 6/24.In most of these eyes, therefore, there is no affection of the L.M. or the L, D., so that neither the retina nor the optic nerve, so far as its connection with the light-sense centre is concerned, need be affected. The cases are too few, however, to permit of dogmatism. So far as the observation goes, it is in accord with Henry's (op.cit.), who also found with his photometer that the L.M. was not affected in toxic-amblyopia.