unit 6 Flashcards
Benefits of Binocular Vision
Single vision
* Stereovision - depth perception
* Increase field of vision
* Compensation for blind spot
Fixation is
Image on fovea and Fixation reflexes to keep image on fovea
Fusion is
single image formed with images from both
eyes
Diplopia is
2 images are perceived; one from each eye;
lack of fusion
Suppression
the brain ignores one of the images
during diplopia
Amblyopia
reduced BCVA if the visual system in the
brain does not receive clear images during
(BCVA
best corrected visual acuity
Oculomotor Control e.g Saccades
Fast movements that keep the image on the
fovea
Smooth pursuits
Slow movements of the eyes to follow an object
Monocular
: includes abduction, adduction, supraduction,
infraduction, intorsion, extorsion
Dextroversion
both eyes looking RIGHT
Levoversion
both eyes looking LEFT
Supraversions
both eyes looking UP
Infraversion
: both eyes looking DOWN
Convergence
both eyes look TOWARDS each other
Divergence
: both eyes look AWAY from each other
Names of EOMs
Superior rectus
* Inferior rectus
* Medial rectus
* Lateral rectus
* Superior oblique
* Inferior oblique
Primary Action of EOMs
Elevation – SR
* Depression - IR
* Adduction - MR
* Abduction - LR
* Intorsion - SO
* Extorsion - IO
Yoke muscles
muscles from each eye that work
together to move the eyes together
Hering’s Law of Equal Innervation
when a muscle in
one eye is sent a message to move, the yoke muscle in the other eye receives equal
innervation.
Sherrington’s Law of Reciprocal Innervation
when a
signal is sent to one muscle to contract the
opposing muscle for that eye is sent a signal to
relax.
Strabismus Definition
the visual axis of the eyes are not aligned
and the eyes appear to be looking in different directions
Amount of deviation : measured in prism diopters Direction of deviation:
eso, exo, hyper, hypo
Esotropia
Inward deviation
Exotropia
Outward deviation
Hypertropia
Upward and downward deviation
Causes of Strabismus
eye turning inwards due to
the focusing efforts as the eyes try to see clearly.
Congenital strabismus
(disease or physical disability
present from birth)
– may require surgery.
Cranial nerve palsies
damage to one of the nerves ◦ e.g CN III, CN IV, CN VI
Decompensated strabismus
develops as an adultlong standing deviation –previously well controlled by
the motor fusional mechanism - now decompensating.
more Causes of Strabismus
Brain damage ( supranuclear structures)
* CN damage (oculomotor nuclei or nerves)
* Direct EOM damage or muscle entrapment in orbital wall fractures
Duane syndrome
incorrect innervation of the EOMs
by the cranial nerves; congenital anomaly. Some muscles stretch when they should tighten, some
stay loose when they should be contracting.
Brown syndrome
: Problem with the SO tendon (too
tight or too short)
* usually congenital but could be secondary to trauma
or surgery
Hirschberg
Shine a light at the eyes and observe where the light
reflex is located in reference to the pupil. For every mm that the light is decentered, the eye is
turned about 15 diopters (7 degrees from center).
Krimsky
Essentially the Hirschberg test, but with prisms
employed to quantify amount of deviation.
◦ Determining how much prism is required to center
the reflex.
◦ Modified Krimsky test = placing prism in front of
fixing eye.
Randot
vectograph random dot stereotest. ◦ Used for detecting amblyopia, strabismus and
suppression, and for assessing stereoacuity. ◦ Can measure stereoacuity from 400 to 20 seconds
of arc.
Stereo fly
Purpose is to measure how minutely the two eyes can
discern differences in the distances of objects from the
observer.
Dissociation tests: for diplopia / suppression
The Worth Four Light Test is also used in detection
of suppression of either the right or left eye.
Normal BSV: Px sees 4: red, 2 green and single white
Diplopia: Px sees 5: 1 red, 2 green and 2 white dots
