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Quantifying the vertical fusion range at four distances of fixation in a normal population.\ud

By K. Ulyat, A.Y. Firth and H.J. Griffiths


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

Year: 2004
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