normal bsv

Question 1

what is normal bsv

Answer 1

ability to use both eyes simultaneously to contribute to a common single perception

one image from one eye and an image from the other eye (slightly dissimilar images)

Question 2

what are the 3 components of bsv

Answer 2

• bifoveal fixation - condition where both eyes are simultaneously directed to the same target - the fovea is the centre part of the maccula - if we dont have a squint and we are using our eyes it is the fovea of our eyes that we are using to see - using both foveas to fix on any given object
• fusion - process of 2 images aligning together to form one image

stereopsis- third and highest degree of normal bsv

Question 3

what are the advantages of normal bsv

Answer 3

allow us to see one image even though we have two eyes

allows us to appreciate depth or 3 dimensional 3d vision

3d vision is known as stereopsis

enlargement of the field of vision

compensation for blind spot and other differences - you have a blind spot in your vision and that is due to the optic disc - the optic disc is a part in your retina that dosnt have any photoreceptors

Question 4

how does bsv develop

Answer 4

some thought bsv was innate and present from birth

others thought that it was developed after birth - acquired/learnt

current - structures and connections (under normal cirucmstances) are present at birth but the system requires use for normal bsv devlopment

3d vision develops in a child at 3-6 months

Question 5

what is the critical period

Answer 5

the visual system is developing up to the age of 7 or 8

if they are past that stage and devlopment has occured and they werent able to develop it you can have problems such as amblyopia

Question 6

what are the benefits of stereopsis

Answer 6

allows us to make fine judgements with resepect to the relative position of objects in space

Question 7

what are the factors necessary for the development of normal bsv

Answer 7

normal anatomical development of the eyes , associated with connections in the brain and the orbital parts of the skull

overlap of visual fields

nasal retinal fibres must cross at the chiasm - allows you to process the scene in the correct order

fovea (area of most distinct vision) must develop normally

normal (retinal correspondence)

normal (retinal) correspondence

Question 8

describe the visual pathway

Answer 8

eyeball

retina

optic chiasm

optic tract

lateral geniuclate nucleus of the thalamus

visual cortex

Question 9

what does their need to be in the visual fields for you to have bsv

Answer 9

• you need to have overlap of the visual fields

- one eye will see a certain amount and then the other eye will seen a certain amount

Question 10

what happens at the optic chiasm

Answer 10

crossing (decussation) of nasal fibres at the optic chiasm

• fibres from the right nasal and left temporal retina relay imformation to the left visual cortex

fibres from the left nasal and right temporal retina relay imformation to the right visual cortex

Question 11

why must the fovea develop normally for normal bsv

Answer 11

• the fovea is a depression in the inner retinal surface
  1. 55mm wide

the photoreceptor layer = entriely cones - specalised for max visual acuity

within the fovea = an fovea avasualr zone - meaning it has no blood vessles

Question 12

what is normal correspondence

Answer 12

a binocular conditon in which the fovea and areas on the nasal and temporal side of the one retina correspond to and have common visual direction with the fovea , temporal and nasal retina of the other eye

• basically the fovea of both eyes have corresponding points - they are basically symmetrical in both eyes

Question 13

describe the fovea in normal correspondence

Answer 13

fovea of left eye corresponds with fovea of right eye

left nasal retina corresponds with right temporal retina

right nasal retina corresponds to left temporal retina

Question 14

how does normal correspondence lead to bsv

Answer 14

sstimulation of corresponding points in each eye results in a single mental image formation

foveas work together as corresponding retinal points

fusion occurs when then the retinal images fall on corresponding points

if objects fall on corresponnding points they will fuse into a single image

Question 15

describe projection in normal bsv

Answer 15

the subjective interpretation of the direction of an object

each retinal element projects to a specific point in space

Question 16

where does the fovea project

Answer 16

the fovea projects straight ahead

the nasal retina projects temporally

the temporal retina projects nasally

the superior retina projects inferioly

the inferior retina projects superiorly

Question 17

describe monocular projection

Answer 17

-an object stimulates the fovea and is projected straight ahead

something that stimulates the nasal retina is prjected temporally and something that stimulates the temporal retina is projected nasally

Question 18

in projection diagrams where is the brain represented

Answer 18

in projection diagrams we represent what the brain ‘sees’ by a third central eye called the cerebral or cylopean

Question 19

what is the horopter

Answer 19

all objects that stimulate corresponding retinal points- i.e. the right nasal retina and the left temporal retina lie on a imaginary line in space called the horopter

if you view a image straight ahead it will stimulate the fovea of the right eye and the fovea of the left eye - these are corresponding retinal points

if you were looking outside the horopter you wouldnt see a single image

therefore if you look at a point on the horopter and you stimulate two corresponding points - you will see the image as single even though you have two eyes

any object lying on or very close to the horopter will be seen singly

Question 20

does everyone have the same horopter

Answer 20

each person has their own horopter for any fixation distance - the locus of all object points that are imaged upon corresponding retinal elements at a given fixator distance

the locus of all object points that are imaged upon corresponding retinal elements at a given fixator distance

Question 21

what is the veith muller horopter

Answer 21

a theoretical determined circle passing through the fixation point and nodal points of each eye

Question 22

what is panums fusional space

Answer 22

a small area around the horopter in which single vision is still present
, so an object may lie slightly ‘’off’’ the horopter but will still be seen singly

panums space is narrow centrally and wider peripherally

if retinal elements stimulated are almost corresponding points the object will still be seen singly as long as it lies within panums fusional space

Question 23

where is panums area narrower and wider

Answer 23

panums area is narrower at the fovea becoming wider at the periphery

the corresponding part of the retina to panums fusional space is panums fusional area

Question 24

what is physiological dipolopia

Answer 24

objects not lying on the horopter or in panums fusional space are seen as double

the double vision or diplopia is a normal physiological occurence in normal bsv

Question 25

what is homonymous or uncrossed diplopia

Answer 25

appreciation that a distant object is double if a near object is fixated

-

Question 26

what is hetronymous diplopia (crossed)

Answer 26

crossed diplopia

appreciation that a near object is double if a diatnce object ias fixated

Question 27

why dont we notice physiological diplopia

Answer 27

the brain ignores or supresses the double images - this is called physiological suppression

brain suppresses everything thats out of panums fusional space

Question 28

descirbe the difference betrween hetronymous and homonymous diplopia

Answer 28

homonymous diplopia - uncrossed dipolpia - seen in esotropia

image falls on the retina nasal to the fovea and projects temporally

hetronymous crossed diplopia

the image falls on the temporal side of the fovea and the image is projected on the temporal retina