In unilateral afferent pupillary defect, when light is moved from the normal to the affected eye, there is (LQ)
|A||Dilatation on the affected side and constriction in the normal eye|
|B||Dilatation in the normal eye and constriction in the affected side|
|C||Dilatation on both pupils|
|D||Constriction in both pupils|
Afferent pupillary defect
1. Absolute afferent pupillary defect (Amaurotic pupil) is caused by a complete optic nerve lesion and is characterised by the following:
a. The involved eye is completely blind (Le. no light perception)
b. Both pupils are unequal in size in light
c. When the affected eye is stimulated by light neither pupil reacts but when the normal eye is stimulated both pupils react normally i.e. consensual response is present.
d. The near reflex is normal in both eyes.
2. Relative afferent pupillary defect. A relative pupillary defect (Marcus Gunn pupil)Qis caused by an incomplete optic nerve lesions or severe retinal disease, dense cataract (opposite eye).
a. Thus the pupils respond weakly to stimulation of the diseases eye and briskly to that of the normal eye.
The difference between the pupillary reactions of the two eyes is highlighted by the 'swinging-flash light test' in which a light source is alternatively switched from one eye to the other and back, thus stimulating each eye in rapid succession.
b. First the normal eye is stimulated, resulting in brisk constriction of both pupils. Then when the light is swung to the diseased eye, both pupils dilate instead of constricting. This paradoxical dilatation of the pupils in response to light occurs because the dilatation produced by withdrawing the light from the normal eye outweighs the constriction produced by stimulating the abnormal eye.
c. In afferent (sensory) lesions the pupils are equal in size. Anisocoria (inequality of pupillary size) Q implies disease of the efferent (motor) nerve, iris or muscles of the pupils.
d. Anisocoria increases in dark → sympathetic paralysis and anisocoria increases in light → parasympathetic paralysis.