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Authors Sidiki, Hamilton and Dutton, are to be congratulated for
bringing the symptoms of nyctalopia in young children to our attention.
Congenital Stationary Night Blindness (CSNB) is difficult to distinguish
clinically from other forms of congenital nystagmus.
The ‘paradoxical pupillary response’ is a helpful finding in
differentiating the condition from other causes. However, Sidiki, Hamilton
and Dutton do not describe this finding accurately. In their paper, the
dilation of a pupil to a bright light stimulus is incorrectly assigned as
the ‘paradoxical pupil response’. Whilst the response described is
paradoxical, since the pupil should constrict to a light stimulus, it is
not the ‘paradoxical pupil response’ found in CSNB. This specific
phenomenon, first described in association with CSNB and achromatopsia,
consists of the initial constriction of the pupil (rather than dilation)
on dimming of the room lighting. Reference 1.
The finding of dilation of a pupil on transferring a light stimulus
from one eye to the other, whilst performing a swinging flashlight test,
reveals a relative afferent pupil defect.
A pupil that dilates, does not constrict, or is sluggish to constrict
after a direct light stimulus is described as having an afferent pupil
defect. Both relative afferent and afferent defects of the pupil are
paradoxical. These findings are usually caused by optic nerve or anterior
visual pathway pathology.
Whilst the finding of the ‘paradoxical papillary response’ is not
currently understood, it does not reflect optic nerve pathology in CSNB.
In the setting of congenital nystagmus, it is highly suggestive of a
retinal dystrophy. Hence, it is important to differentiate an afferent
papillary defect from the ‘paradoxical pupillary response’, because the
causes, and hence investigations, are different.
Furthermore, the finding of a ‘paradoxical pupillary response’ may not be
present in all cases of CSNB. It can be dependent on age, being present
after six months of age and absent in adulthood.
Sidiki, Hamilton and Dutton have written an excellent article on
CSNB, but this should not allow the perpetuation of a common
misunderstanding of terminology which has clinical significance.
References:
1 Barricks ME, Flynn JT, Kushner BJ. Paradoxical pupillary responses
in congenital stationary night blindness. Archives of Ophthalmology 1977;
95(10):1800-4
A pupil response that is paradoxical is not the same as a ‘paradoxical pupillary resonse’
Authors Sidiki, Hamilton and Dutton, are to be congratulated for
bringing the symptoms of nyctalopia in young children to our attention.
Congenital Stationary Night Blindness (CSNB) is difficult to distinguish
clinically from other forms of congenital nystagmus.
The ‘paradoxical pupillary response’ is a helpful finding in
differentiating the condition from other causes. However, Sidiki, Hamilton
and Dutton do not describe this finding accurately. In their paper, the
dilation of a pupil to a bright light stimulus is incorrectly assigned as
the ‘paradoxical pupil response’. Whilst the response described is
paradoxical, since the pupil should constrict to a light stimulus, it is
not the ‘paradoxical pupil response’ found in CSNB. This specific
phenomenon, first described in association with CSNB and achromatopsia,
consists of the initial constriction of the pupil (rather than dilation)
on dimming of the room lighting. Reference 1.
The finding of dilation of a pupil on transferring a light stimulus
from one eye to the other, whilst performing a swinging flashlight test,
reveals a relative afferent pupil defect.
A pupil that dilates, does not constrict, or is sluggish to constrict
after a direct light stimulus is described as having an afferent pupil
defect. Both relative afferent and afferent defects of the pupil are
paradoxical. These findings are usually caused by optic nerve or anterior
visual pathway pathology.
Whilst the finding of the ‘paradoxical papillary response’ is not
currently understood, it does not reflect optic nerve pathology in CSNB.
In the setting of congenital nystagmus, it is highly suggestive of a
retinal dystrophy. Hence, it is important to differentiate an afferent
papillary defect from the ‘paradoxical pupillary response’, because the
causes, and hence investigations, are different.
Furthermore, the finding of a ‘paradoxical pupillary response’ may not be
present in all cases of CSNB. It can be dependent on age, being present
after six months of age and absent in adulthood.
Sidiki, Hamilton and Dutton have written an excellent article on
CSNB, but this should not allow the perpetuation of a common
misunderstanding of terminology which has clinical significance.
References:
1 Barricks ME, Flynn JT, Kushner BJ. Paradoxical pupillary responses
in congenital stationary night blindness. Archives of Ophthalmology 1977;
95(10):1800-4
Competing interests:
None declared
Competing interests: No competing interests