Influence of convergence on vertical fusional vergence amplitude

• Purpose: Deficiency in vertical fusional vergence amplitude (VFVA) is known to cause asthenopia and oculomotor imbalances. The measurement of VFVA however is confounded by its increase with convergence (Hara et al., 1998). A quantitative relationship between the two vergences is thus necessary to predict the VFVA at a given convergence angle. Here, we sought to derive such a relationship by measuring the VFVA at a range of convergence angles. Methods: 30 subjects (17–21 yrs) wearing red-green goggles fused a pair of red-green concentric circles projected on a computer monitor at a distance of 50 cms in a dark room. The horizontal and vertical separation between the red-green circles determined the convergence and vertical vergence demand respectively. The VFVA was measured at 8 equally spaced convergence demands ranging from 0.58° to 11.13°. The convergence demands were either systematically increased or randomly varied across different sessions. in each session, the convergence demand was kept constant while the vertical vergence demand was varied in steps of 0.03°. The maximum vertical vergence demand that could be fused determined the VFVA. Results: The subjects’ data was divided into four groups based on the range of convergence demands that could be fused. in all the groups, the VFVA increased linearly with the systematic increase in convergence demand (mean regression equation: y 0.15x 0.49). Randomizing the convergence demands did not show any significant change in this relationship (y0.12x 0.80). Conclusion: The VFVA increases linearly in the range of convergence demands tested. The linear regression equation derived could be used in a clinical setup to predict the VFVA at a given convergence angle

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Oftalmologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Ophthalmology (hsv//eng)

Nyckelord

Optometry

Optometri

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