XT still D>N after 1-hour monocular patch or with +3D lens
Pseudo / Simulated
XT D=N after:
1 hour monocular patch (“fusional”)
+ 3D lens (“accommodative”)
Exo deviations for near are controlled by fusional convergence. This control can be abolished by dissociating the eyes with monocular occlusion or removing accommodative drive with a +3D lens. In pseudo-divergence excess, this causes the XT for near to increase to the same degree as that for distance (i.e. it breaks down to a basic XT). The significance of this is debated.
± Comitant XT
XT Distance (D) > Near (N)
D = N
D < N
If divergence excess, test for divergence excess or pseudo-divergence excess by remeasuring after 1 hour of monocular occlusion. If divergence excess is confirmed, test with +3D lenses to differentiate between true and simulated divergence excess, see above)
Only evident with cover test and controls rapidly
Controls after blink
Controls after 5 - 10 seconds
Does not regain control / breaks spontaneously
The XT is often worst when asking the patient to look in the far distance (e.g. out a window). However, this may be difficult to examine in young children
These methods are rarely definitive, but can be used to delay surgery until the child is older. There is little consensus between clinicians / orthoptists as to best practice
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