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FIXATION CHARACTERISTICS AND ANOMALIES
By: Noor Munirah binti Awang Abu Bakar
Optometrist (Moc No: O-0869)
OUTLINES:• Binocular vision • Eye movements• Types of eye movements• Eye Fixation- Concepts• Eye Fixation- Components• Fixation abnormalities
BINOCULAR VISION• Binocular vision is a sensorimotor process.• Eye movements to keep lines of sight pointing
same target.
(Otero-Millan et al, 2014)
EYE MOVEMENTSWhat? Refers to voluntary or involuntary movement of the eyes,
helping in acquiring, fixating and tracking the visual stimuli. Eye movements place the image of interest on the fovea
(part of retina with highest acuity) Controlled by 6 extraocular muscles innervated by cranial
nerves III, IV and VI.
EYE MOVEMENT CONTROLLED BY 6 EXTRAOCULAR MUSCLES (SUPERIOR VIEW)
TYPES OF EYE MOVEMENT
(Ciuffreda & Tannen, 1995)
EYE FIXATION Question:
Do our eyes move or still during fixating on a stationary object?
Answer:
Moving
EYE FIXATION-CONCEPT During attempted visual fixation at a stationary object,
our eyes continually move involuntarily.
The movement can be slow or rapid small amplitude- make us unaware of the movement.
The fixational eye movements change the degree of alignment between 2 eyes and continuously move the retinal images.
Even there is movement, the image of the object is still retained within an acceptable foveal retinal locus. (±30 minutes of arc)
(Ciuffreda & Tannen, 1995)
EYE FIXATION-CONCEPT
EYE FIXATION-CONCEPT 1.Our eyes are focusing at a fly
EYE FIXATION-CONCEPT2. At macular area, there is a central foveal fixation point.
Macula
EYE FIXATION-CONCEPT3. At macular area, there is a central foveal fixation point.
EYE FIXATION-CONCEPT4. Central fovea is highly dense with cone photoreceptor.s
EYE FIXATION-CONCEPT5. During the eye fixation, the image moving in the central
fovea (across a cone, a dozen to hundreds of photoreceptors).
EYE FIXATION-CONCEPT
(Otero-Millan et al, 2014)
While our eyes are constantly moving, why we do not suffer DIPLOPIA?
EYE FIXATION-CONCEPT
(Martinez-Conde et al., 2004)
EYE FIXATION-CONCEPTALTERNATE EYE SACCADE AND FIXATION
• This is the typical pattern of eye movement during reading.
•The eyes never move smoothly over still text.
•Fixation lengths ~ 100 to 600 milliseconds length shows information processing.
• During this stop the brain starts to process the visual information received from the eyes
An example of fixations and saccades over text
EYE FIXATION-CONCEPTPATTERN FOR SHOWING FIXATIONAL EYE MOVEMENTS
To experience it, look at the central black dot for about a minute, then look at the white dot in the adjacent dark square.
The dark after-image of the white line pattern should be seen in constant motion owing to fixational eye movements.
EYE FIXATION-COMPONENTS
NEED TO UNDERSTAND…
EYE FIXATION COMPONENTS Microsaccades
( Martinez-Conde et al, 2004 & Otero-Millan et al, 2014)
EYE FIXATION COMPONENTS Tremors
( Martinez-Conde et al, 2004 & Otero-Millan et al, 2014)
EYE FIXATION COMPONENTS Drifts
( Martinez-Conde et al, 2004 & Otero-Millan et al, 2014)
TREMOR, DRIFT & MICROSACCADES ACROSS PHOTORECEPTORS
Curved lines: High frequency tremors & drifts
Straight lines: -Fast, jerk-like movements of microsaccades-Bring the image back towards the centre of vision
Fovea diameter: 0.05mm
EYE FIXATIONEYE MOVEMENTS DURING VISUAL FIXATION
• An observer views a picture (left) while eye positions are monitored (right).
• The eyes jump, seem to fixate or rest momentarily, producing a small dot on the trace, then jump to a new region of interest.
• However, even during these fixation, or ‘rest’ times, the eyes are never still, but continuously produce fixational eye movements — drifts, tremor and microsaccades.
EYE FIXATION
VISUAL FADING: TROXLER’S EFFECT
1. Fixate at red spot.
2. After few secs, bluish
annulus will disappear.
3. Red spot surrounded by
white field.
FIXATIONAL EYE MOVEMENT:MONOCULAR VS BINOCULAR VIEWING
Binocular performance can be superior to monocular performance of the same visual task. Why? Binocular summation – An ability of the brain to combine the
info from two eyes. Binocular summation predicts improved fixation stability
under binocular viewing as compared to monocular viewing.
Increased fixation instability during monocular viewing, especially for the occluded eye (González et al.,2012)
FIXATIONAL EYE MOVEMENT:NEAR VS FAR VIEWING
No differences in fixational eye movement characteristics between far and near viewing (Krauskopf et al., 1960)
FIXATION ABNORMALITIES
(Ciuffreda & Tannen, 1995)
FIXATION ABNORMALITIES
(Ciuffreda & Tannen, 1995)
FIXATION ABNORMALITIES
(Ciuffreda & Tannen, 1995)
FIXATION ABNORMALITIES
(Ciuffreda & Tannen, 1995)
FIXATION ABNORMALITIES2. Saccadic intrusions
(Ciuffreda & Tannen, 1995)
2. Saccadic intrusions
FIXATION ABNORMALITIES
(Ciuffreda & Tannen, 1995)
FIXATION ABNORMALITIES3. Nystagmus- Involuntary rhythmic oscillation of the eye
(Ciuffreda & Tannen, 1995)
FIXATION ABNORMALITIESPe
ndul
ar N
ysta
gmus
(Ciuffreda & Tannen, 1995)
FIXATION ABNORMALITIESJe
rk N
ysta
gmus
(Ciuffreda & Tannen, 1995)
3. Nystagmus- Involuntary rhythmic oscillation of the eye
FIXATION ABNORMALITIES
3. Nystagmus
FIXATION ABNORMALITIES
REFERENCES Ciuffreda, K.J. 1995. Eye Movement Basics for The Clinician. Mosby. Martinez-Conde, S. Macknik, S.L. & Hubel, D.H. Role of Fixational Eye in
Visual Perception. Nat Rev Neurosci. 2004 Mar;5(3):229-40. Martinez-Conde, S. Fixational Eye Movements in Normal and Pathological
Vision. Prog Brain Res. 2006;154:151-76. Otero-Millan, J., Macknik, S. & Martinez-Conde, S. Fixational Eye Movements
and Binocular Vision. Front Integr Neurosci. 2014; 8: 52. Published online 2014 July 7. doi: 10.3389/fnint.2014.00052 PMCID: PMC4083562
Rucci, M. & Poletti, M. Control and Functions of Fixational Eye Movements. Annual Review of Vision Science, Vol. 1: 499 -518 (Volume publication date November 2015)
Shaikh A.G. , Otero-Millan J., Kumar P., Ghasia F.F. Abnormal Fixational Eye Movements in Amblyopia. PLoS One. 2016 Mar 1;11(3):e0149953. doi: 10.1371/journal.pone.0149953. eCollection 2016.