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Sara M Flodin, Tony Pansell, Agneta Rydberg, Marita Andersson Gronlund; Cyclofusion ranges in a healthy adult population. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1017.
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Cyclovergence is the simultaneous cyclorotation of both eyes, performed in opposite directions to obtain or maintain binocular single vision (BSV), and ensures cyclofusion. To date, cyclovergence has only been estimated or observed objectively and subjective cyclofusion ranges are unknown. This study hypothesize that subjective cyclofusion can be measured in a healthy non-strabismic adult population using a standard clinical test, to establish clinical reference ranges.
A cross-sectional investigation was performed on a random sample group of 60 healthy, non-strabismic adults (30 women, 30 men) in the age range of 18-69 years (median age 43 years). Cyclofusion was investigated using the synoptophore and fusion slides. Once sensory fusion was proved, motor fusion was tested. Break of fusion was recorded for incyclovergence and excyclovergence when the patient reported break of single image, tilting of image or suppression of one of the controls. The amplitude was the total amount of torsion fused between the in and excyclotorsion values recorded at breakpoints. Data analysis showed normal distribution, and the anova was used for statistical analysis.
Subjects in all age groups showed low values of cyclotorsion, mainly excyclotorsion. Mean values for the whole sample was -1 degrees (SD 1.61). Cyclofusion showed a total amplitude of 16 degrees (SD 3.96). Excyclo range was larger than the incyclo range, measuring -9 degrees (SD 2.59) and +7 degrees (SD 1.97) respectively. There was no age or gender related effect on cyclofusion range (p=0.59).
This is the first study providing true subjective scientific measures on a normal population for assessing cyclofusion in adults. A reference range for clinical guidance has been established. Values outside of the reference range are not necessarily pathologic or abnormal, but indicators of possible binocular abnormalities as well as physiological variations. The results suggest that cyclotorsion >9° interferes with vergences, dissociating BSV. Patients, who complain of problems with double vision or maintaining binocularity without other obvious strabismic cause, should be assessed for cyclotorsion. If increased values of cyclotorsion are found, further investigations of fusion capacity with horizontal vergence control and cyclofusion amplitudes should be prompted.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
The Haag-Streit Clement Clarke Synoptophore model 2003.
Fusion slides F9/10 used when testing cyclofusion
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