W19 Spacial Localisation and Visual Direction

What is visual direction?

Visual system has to be able to determine the direction of visual stimuli in order to respond appropriately

What does oculocentric mean?

Centred on that specific eye

What is the principal visual direction?

Corresponds to the visual axis that projects from the fovea

What are secondary visual directions?

All other points on the retinal have secondary visual directions (O) located with respect to the fovea

What is Lotze’s local sign?

Each retinal receptor has a unique oculocetric direction

What does egocentric mean?

Means focused on that particular person

How do we perceive the world?

As though we have a cyclopean eye in between the 2 real ones

What is the method to finding your cyclopean eye?

• Point fingers at distant object with both eyes open

• Keep fingers still- observe alignment of fingers to distant object when looking through LE and RE

• Through LE, fingers will point right, through RE, fingers will point left- fingers line up according to dominant eye

What is the dominant eye?

The eye that contributes most to the visual percept

Why may it be clinically useful to identify the dominant eye?

• Dominant eye has slightly higher VA

• ARMD will affect px more in dominant eye

• Slight under correction may be more tolerated in non-dominant eye

What are corresponding points?

To maintain single vision, the corresponding points have the same visual direction when stimulated separately

What is the horopter?

Any image positioned on the horopter (green line) will stimulate corresponding retinal points- the object will be seen in single vision

What was the Vieth Muller circle?

The theory that the shape of the horopter had perfect ocular symmetry (circular, not elliptical)

What are disparate points?

Objects which are not on the horopter stimulate retinal elements which are disparate points- they don’t have identical visual directions and double vision of the object OFTEN occurs- this is physiological diplopia

What is Panum’s fusional area?

Each point on one retina corresponds to an area of points on the other retina called Panum’s fusional area- the stimulation of which allows 2 monocular inputs

What is Panum’s fusional space?

Binocular single vision occurs over a small distance in front and behind the horopter- called Panum’s fusional space- PHYSIOLOGICAL DIPLOPIA OCCURS ONLY OUTSIDE THIS SPACE

What is crossed (heteronymous) diplopia?

RE image seen on LHS and vice versa-

What is uncrossed diplopia?

LE image seen on LHS and vice versa