Rod monochromatism and blue cone monochromatism: pupillary, accommodative and convergence reactions to darkness

To elucidate the mechanism of paradoxical pupillary constriction to darkness (PPCD) and the clinical characteristics facilitating this phenomenon.

Six rod monochromats, three blue cone monochromats, with three obligate BCM carriers, and ten age matched controls were studied. Pupillary responses, refractions and eye positions were measured with an infrared refractometer, with and without background room lighting while being simultaneously recorded on VHS (infrared) video tape from onset of darkness.

Only rod monochromats displayed typical paradoxical pupillary responses. Blue cone monochromats and obligate BCM carriers showed reduced pupillary contraction, compared to controls, but no paradoxical pupillary reaction. Changes neither in accommodation nor convergence were found during paradoxical pupillary constriction to darkness in our rod monochromats.

Paradoxical pupillary constrictions to darkness were seen in rod monochromats but were found not to be age or gender related. This constriction was accompanied neither by accommodation nor convergence changes. No significant differences in pupillary responses to darkness were observed in BCMs nor their carriers, although pupillary dilation to darkness seemed slightly impaired as compared to normals.