V pattern
A vertically incomitant horizontal strabismus where the deviation increases in a specific vertical gaze direction. In V-pattern exotropia, the outward deviation is greater in upgaze compared to downgaze or primary position. In V-pattern esotropia, the inward deviation is greater in downgaze compared to upgaze or primary position. The difference between upgaze and downgaze deviations must be at least 15 prism diopters to be considered clinically significant.
vectogram
A polarized stereogram that presents a different image to each eye, allowing for the perception of depth. It consists of two photographic images printed on opposite sides of a transparent film, with their axes of polarization oriented at right angles to each other. When viewed through polarized filters, each eye sees only one image. Vectograms are commonly used in vision therapy to improve binocular vision skills, including convergence, divergence, and stereopsis.
vergence
The simultaneous movement of both eyes in opposite directions to maintain single binocular vision. Convergence is an inward rotation of the eyes, while divergence is an outward rotation. Driven by retinal disparity, blur, and proximal cues, vergence works in conjunction with saccades to quickly align the eyes. .
vergence facility
A measure of how quickly and accurately the fast fusional vergence system responds to rapidly changing vergence demands. Typically tested using prism flippers, the patient alternates fusion through 3Δ base-in and 12Δ base-out prisms at near, and the cycles per minute (cpm) are recorded. Reduced vergence facility (<15 cpm) can indicate binocular vision disorders. This dynamic test reflects vergence automaticity, as opposed to slow fusional vergence ranges.
vertical offset-setting (of the horizontal recti)
Reattaching the medial and lateral rectus muscles at a new scleral insertion point that is vertically displaced from the original insertion, usually between 1/2 to 1 full tendon width higher or lower. Moving the medial rectus insertions downward decreases adduction in downgaze, treating A-pattern esotropia. Moving the lateral rectus insertions upward decreases abduction in upgaze, treating A-pattern exotropia. The opposite vertical transpositions treat V-pattern strabismus by increasing the horizontal deviation in the opposite field of gaze.
visual confusion
A phenomenon that can occur in strabismus when the foveas of the two misaligned eyes are fixating on different objects. The brain perceives the two dissimilar objects as occupying the same visual direction, causing them to appear superimposed. Visual confusion is more likely to be experienced in acute strabismus before suppression mechanisms develop to avoid double vision.
visual evoked potentials
Electrophysiological signals recorded from the visual cortex in response to visual stimulation. VEPs assess the functional integrity of the visual pathways from the retina via the optic nerves to the occipital cortex. Electrodes placed on the scalp measure the electrical activity elicited by flash, pattern reversal, or pattern onset/offset stimuli. Abnormalities in VEP waveform latencies or amplitudes can indicate dysfunction within the visual system.
visuoscope
An ophthalmoscope adapted with a small, central fixation target that projects a shadow onto the retina to assess monocular fixation in amblyopia. The position of the shadow relative to the fovea indicates the type of fixation. Visuoscopy allows direct observation of the retinal fixation point, requiring patients to voluntarily fixate the target. It assumes the foveal reflex accurately demarcates the foveal center.