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Anisometropia.
349 children (11.3% of total) included in the above tables shewed a difference of vision
between the two eyes, of which 227 were boys and 122 girls. Of these, 61 boys shewed a
difference of natural vision of one Snellen line and 6 had a difference of two lines. With
+ 1 sphere added 17 of the 61 boys had a difference of one Snellen line between the eyes and
3 boys had a difference of two lines, the remaining 41 boys having similar vision in each eye.
The addition of + 1 sphere to the 6 boys shewing a difference of natural vision of 2 lines
caused 4 to have similar vision between the eyes and 2 to differ by one line.
33 girls had a difference of natural vision of one Snellen line, and 2 had a difference
of two lines. With + 1 sphere 8 of the 33 girls had a difference of one line, one had two
lines difference, whilst 24 had similar vision in each eye.
The two girls with a difference of two lines natural vision had a difference of one line
only with the addition of + 1 sphere.
The remaining 160 boys and 87 girls shewed a difference in vision between the eyes
only after + 1 sphere was added.
Boys. 141 had a difference of 1 Snellen line.
16 ,, ,, „ 2 „ lines.
3 ,, ,, „ 3 „ lines
Girls. 72 ,, ,, ,,1 ,, line.
11 ,, ,, ,,2 ,, lines.
4 ,, ,, „ 3 „ „
Summarised this gives Natural Anisometropia 3.3%
Anisometropia with + 1 sphere 8.0%
Total 11.3%
It will be seen that the tables show no instance of a child's vision being improved by
the addition of the + 1 sphere. Actually one boy and one girl had a slight increase of vision
in one eye, with a decrease in the other. As the decrease was the greater they have been
classified under that heading. The absence of improvement of vision does not necessarily give
a true picture since the School Test cards do not usually have a 6/5 line, therefore, any child
seeing 6/6 who might be improved by the addition of + 1 sphere would merely be reported
as " No change."
The two columns "Increase" and "No change" however should indicate Hypermetropia,
and therefore it would appear that 9.6% of the children tested were Hypermetropic,
who, since they had good vision and no subjective symptoms, do not require further consideration.
The remaining 90.4% were all adversely affected by the addition of the + 1 sphere and
therefore according to the Report of the Committee of Inquiry should be either Emmetropic
(normal vision) or Myopic. I feel, however, that small degrees of Hypermetropic Astigmatism
of less than 1 diopter would probably account also for a diminution of vision with an
added + 1 sphere.
Since this report is based on loutine work and is not a Special Inquiry it has been
impossible to do refractions to prove or disprove this, but some of the special refractions given
later show that this does occur. The point however is not of practical importance, since mild
degrees of hypermetropic astigmatism with no symptoms and good vision would need no treatment
until symptoms arose.
The essential problem however is to distinguish the early myopes, and without refraction
it is impossible to do this with certainty. In passing, however, it may be noted that the
emmetropes present a minor problem, as in the gowing child the tendency is for the eyes to
become more myopic, consequently emmetropia may be only the mid-stage in the passage from
infantile hypermetropia to the myopia of the older child. Therefore, in order to safeguard the
vision of growing children, it should be necessary to follow-up, at least by more frequent
testing, those children who are emmetropic as well as those who are slightly myopic.
Obviously, however, those children who are already slightly myopic are the more
important.
90.4% of the children tested must therefore be considered as either emmetropic, slightly
myopic or possibly with a low degree of hypermetropic astigmatism. The number is too large to
make refraction of all the children possible in the routine work. Had this been done it would
have meant an addition of 2,770 refractions, which is five times as many as those done in the
ordinary course of treatment.
I suggested, however, last year that a working standard might be taken which would
catch the early myopes, and it is obvious that it is the larger degrees of diminution which are
the most likely to be myopes. In view of this year's figures it would seem practicable to
refract all children whose vision with + 1 sphere is diminished by five or more Snellen lines.
This represents 0.81% of the total children or 25 in actual figures.
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