Binocular Single Vision (BSV)

• Fusion- seeing a single image formed from two eyes

  • motor

  • sensory

  • simultaneous perception

  • stereopsis

The Synoptophore

manifest:

• visual axes do not align when veiwing binoculary ( seen without cover )

• aka strabismus, heterotropia, squint ( no fusion)

• deviation in one eye only ( specify eye)

• angle btwn visual axes does not change

Latent

• visual axes align when vewing binoculary ( only seen when CT)

• aka heterophoria (motor fusion interrupted by occluder)

• deviation in both eyes ( dont record eye)

• angle btwn visual axes changes

IC

• caused by fault with one or more EOMs

• only there when we are looking in the direction that affected msc is used

CD- angle of deviation remains constant with different directions of gaze, BUT NOT necessarily with different viewing distances

crossed = exotropia

uncrossed- esotropia

• Abnormal retinal correspondence ( ARC)

  Binocular

• overcomes diplopia and confusion

Versions:

• chnage direction of gaze

• conjugate ( both move by the same amt)

• angle btwn visual axes doesnt change

Vergences:

• change in distance ( divergence is passive, convergence is active)

• angle btwn visual axes changes

  • Convergence = contraction of MR ( IIIrd nerve)

  • Divergence = contraction of LR (VIth nerve)

SP- voluntary, keeps image on ret, 30’ per second, movng object needed

(tested with motility)

Saccades- voluntary, quick jerk mvts, 900’ per second, eg reading

Micro-saccades- involuntary, much smaller than saccades

Hering's Law of Equal Innervation- each pair of msc move same amt at same time. Refers to versions, not vergence. eg. RLR and LMR

Sherrington's Law of Reciprocal Innervation - when one msc receives innervation to contract, its direct antagonist relaxes ( same eye with opposite action) eg RSR and RIR

• excessive accomodation ( uncorrected hyperopia) = excessive convergence

• uncorrected hyperope show eso deviations

• if motor fusion adequate = esophoria. If not = esotropia

• uncorrected myope show exo deviation

• 1DS = 4prism dioptres

AKA:

- Prism fusion range

- Fusional vergence range

- fusional reserves

- Fusional amplitude

• needed to maintain motor fusion with eye mvts + overcome/neutralise any latent deviation

• light is deviated towards base + object appears displaced towards the apex

• prism measures amplitude of deviation

• EXO = base IN (dIvergent fusion range)

• ESO= base OUT ( cOnvergent fusion range)