Paradoxical Pupillary Constriction to Darkness

Another useful test is the "paradoxical pupillary constriction to darkness."1,5,6 Figure 2-4 illustrates this phenomenon. As the room lights are turned off, the pupils, instead of dilating, will

Normal

Paradoxical

Lights on

oo

OO

Lights off

oo

oo

Lights off > 30 sec

oo

oo

FIGURE 2-4. The paradoxical pupillary response to darkness is a momentary pupillary constriction immediately upon decreasing room illumination.

FIGURE 2-4. The paradoxical pupillary response to darkness is a momentary pupillary constriction immediately upon decreasing room illumination.

TABLE 2-3. Paradoxical Pupillary Phenomena.

Common causes

Congenital stationary night blindness Congenital achromatopsia Optic nerve hypoplasia Rare causes

Leber's congenital amaurosis

Best's disease

Albinism

Retinitis pigmentosa momentarily constrict. After 2 to 10 s the pupils will undergo slow dilatation; this is best seen by providing some low-level side illumination as the lights are dimmed. This "paradoxical pupillary constriction to darkness" is indicative of optic nerve or retinal disease or both (Table 2-3).

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