The relative afferent pupillary defect and a novel method of fusion recovery with the Worth 4-dot test
L. N. Johnson
Neuro-Ophthalmology Unit, Mason Institute of Ophthalmology, University of Missouri-Columbia, USA.
OBJECTIVE: To examine the relation of the relative afferent pupillary
defect and commonly used clinical tests of visual cortex binocular cell
activity, namely, fusion and stereopsis. METHODS: Sixty-seven subjects with
neuro-ophthalmologic disorders underwent measurement of relative afferent
pupillary defect and assessment of binocular sensory status by fusion on
the Worth 4-dot test and stereopsis on the Titmus stereo test. Recovery of
fusion on the Worth 4-dot test and improvement of stereopsis were tested by
placing increasing neutral density filters in front of the eye that did not
have the afferent pupillary defect. RESULTS: Recovery of fusion on the
Worth 4-dot test occurred with use of neutral density filters (Worth 4-dot
neutralization test). No improvement of stereopsis was observed. A
significant positive association was identified between the measured
afferent pupillary defect and the measured log filter required for fusion
(r = .83, P < .001 by the Spearman rank correlation coefficient). In no
case was a relative afferent pupillary defect observed when fusion without
use of neutral density filters was present at baseline. For subjects with
relative afferent pupillary defects, the measurements of the Worth 4-dot
neutralization test were equal before and after pupillary dilation.
CONCLUSIONS: The relative afferent pupillary defect is a dynamic process
that results from an imbalance of brightness sensitivity between the two
eyes. Altering the latency ("timing") and amplitude of the light stimuli by
use of neutral density filters can restore fusion on the Worth 4-dot
neutralization test but does not alter stereopsis. The Worth 4-dot
neutralization test may be a useful adjunct in the assessment of visual
dysfunction.
