New tests of distance stereoacuity and their role in evaluating intermittent exotropia.
OBJECTIVE
Poor control of intermittent exotropia has been considered an indication for surgical intervention, and poor distance stereoacuity may be an indicator of poor control. Two new measures of distance stereoacuity, the Frisby-Davis Distance test (FD2) and Distance Randot test (DR), both of which have been validated in normal and strabismic subjects, were evaluated, and we compared stereoacuity with scores on a recently described control scale.


METHODS
Prospective case series.


METHODS
Twenty-five consecutive patients with intermittent exotropia.


METHODS
Office-based control was graded at distance and near on a 0 to 5 scale, and distance control ranged from 1 (recovery in 1-5 seconds after monocular occlusion) to 4 (>50% spontaneously tropic). Stereoacuity was measured using the FD2 and DR at distance and the Preschool Randot and Frisby tests at near.


METHODS
Distance stereoacuity measured using the FD2 and DR.


RESULTS
Measurable distance stereoacuity thresholds in intermittent exotropia were poor with the DR and excellent with the FD2 (medians, nil and 40''; P<0.0001). Near stereoacuity was excellent with both the Preschool Randot and Frisby (medians, 60'' and 60''; P = 0.99). There was poor correlation between distance control score and either FD2 (r(s) = 0.1, P = 0.6) or DR (r(s) = 0.3, P = 0.2). Control scores correlated with magnitude of deviation at distance (r(s) = 0.5, P = 0.02) and near (r(s) = 0.5, P = 0.01).


CONCLUSIONS
The real-world contour-based targets of the new distance FD2 appear to stimulate fusion in intermittent exotropia, even when distance control is poor. In contrast, the new Polaroid vectograph-based DR is very sensitive to disturbances of binocularity. Two new distance stereoacuity tests appear sensitive to opposite ends of the intermittent exotropia spectrum; FD2 performance deteriorates when the patient is constantly tropic, whereas DR performance deteriorates at the earliest stages of intermittency.
Holmes
Jonathan M
JM
Department of Ophthalmology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA. holmes.jonathan@mayo.edu
Birch
Eileen E
EE
Leske
David A
DA
Fu
Valeria L
VL
Mohney
Brian G
BG
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003867:Depth Perception / Q000502:physiology*; D005099:Exotropia / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D011446:Prospective Studies; D014787:Vision Tests / Q000379:methods; D014792:Visual Acuity / Q000502:physiology*