An anisocoria produces a small relative afferent pupillary defect in the eye with the smaller pupil.
OBJECTIVE
To determine whether an anisocoria can produce a relative afferent pupillary defect of clinical importance.


METHODS
Anisocoria and relative afferent pupillary defect were measured with infrared videography in three clinical experiments: 1) every few minutes in eight normal subjects who remained in darkness as one pupil was dilating from mydriatic drops; 2) every 2 hours, for 8 hours in six normal subjects who remained in room light after one pupil was dilated with mydriatic drops; and 3) before and after dilation of one pupil in 24 patients with known afferent defects from optic nerve disease and who remained in room light.


RESULTS
In the presence of an anisocoria, the relative afferent pupillary defect was almost always in the eye with the smaller pupil. The results of the three experiments were: 1) In darkness, the induced pupillary defect was found to be related to the ratio of the areas of the two pupils (R = 0.942), and 0.14 log unit of pupillary defect was produced in the eye with the smaller pupil for every millimeter of anisocoria. 2) In room light, the induced pupillary defect was in the eye with the smaller pupil but was less than in Experiment 1 and persisted throughout the 8 hours. This was presumably because the eye with the larger pupil had become more light adapted in the clinic light than the eye with the smaller pupil. 3) In room light, inducing an anisocoria in patients with preexisting afferent pupillary defect tended to shift the pupillary defect toward the eye with the smaller pupil (R = 0.68).


CONCLUSIONS
Clinically, approximately 0.1 log unit of relative afferent pupillary defect is produced in the eye with the smaller pupil for every millimeter of anisocoria. Therefore, the anisocoria must be larger than 2 mm in diameter difference to induce a clinically significant relative afferent pupillary defect.
Lam
B L
BL
Bascom Palmer Eye Institute, University of Miami, Florida, USA.
Thompson
H S
HS
D015875:Anisocoria / Q000150:complications* / Q000503:physiopathology*; D003624:Darkness; D006801:Humans; D007499:Iris Diseases / Q000209:etiology*; D008027:Light; D015878:Mydriasis; D011680:Pupil / Q000528:radiation effects; D013997:Time Factors