9 research outputs found
Quantifying the vertical fusion range at four distances of fixation in a normal population.
Aim: To compare the vertical fusional amplitudes in
isometropic participants with normal binocular
single vision at four distances of fixation: 33 cm,
1 m, 4 m, 6 m.
Methods: Vertical fusion ranges (break point and
recovery point) were measured with a Gulden
vertical prism bar with the participant fixing a 6/12
Snellen equivalent letter, twice at each distance.
Order effects were controlled with randomisation of
both fixation distance and prism direction.
Results: Twenty-seven participants were examined
(aged 20.4 ± 1.05 years). Base up and base down
measurements were similar, therefore measurements
were combined to give a total vertical range. Median
values for the break points were: 33 cm, 6(Δ) ; 1 m, 6(Δ);
4 m, 5.5(Δ); 6 m, 5.5(Δ); and for the recovery points were:
33 cm, 4(Δ); 1 m, 4(Δ); 4 m, 3.5(Δ); 6 m, 3.5(Δ). The
difference was significant between either of the near
measures (i.e. 33 cm and 1 m) and either of the far
measures (i.e. 4 m and 6 m).
Conclusions: The vertical fusion range appears to be
slightly greater at near than distance. However, the
difference is not clinically significant. Measurements
for distance, in a normal population, appear to be the
same whether a fixation distance of 4 m or 6 m is
used