Walton states that ‘doubtless various factors play an important part in producing the dilated pupil, but if disorders of any simple mechanism are to be credited with the production of the Hutchinson pupil or other pupillary changes, the only lesion worthy of the place is disturbance, irritative or paralytic, of the intracranial fibres of the cilio-spinal tract’.
The late Professor von Bergmann, from 70 cases, reports as follows:—
In 39 cases both pupils were markedly dilated (56 per cent.).
In 7 cases both pupils were markedly contracted (10 per cent.).
In 20 cases the pupil on the same side was dilated (30 per cent.).
In 4 cases the pupil on the opposite side was dilated (6 per cent.).
Parsons, in answering some queries in 1903, writes:—
‘I should anticipate from cortical irritation bilateral pupillary dilatation, perhaps more marked on the opposite side: from pressure the opposite effects, so far as mere cortical paralysis goes, but this would be more liable to be vitiated by vascular changes—the complex condition seen in coma. It is very difficult to elicit pupillary constriction by cortical stimuli—very easy to elicit dilatation, but always bilateral though often more marked on the opposite side.’
In cases examined by me the following conditions were found:—
| Pupils equal | 46 | per cent. of cases |
| Pupils constricted on the affected side | 36 | per cent. of cases |
| Pupils dilated on the affected side | 18 | per cent. of cases |