introd to binocular vision Flashcards
(23 cards)
definition of binocular vision?
Binocular vision is the ability to use two eyes together simultaneously, such that each eye contributes to a single perception of the visual world.
What are the two key processes required for binocular vision?
Sensory fusion (neural process) and motor fusion (alignment of the eyes).
What are the four basic requirements for binocular vision?
Two eyes with overlapping visual fields.
Coordinated eye movements ensuring the fields of fixation overlap.
Neural transmission of light impulses from both eyes must reach the same brain area.
Perceptual blending or fusion of impulses from both eyes must occur in higher brain levels.
What are the benefits of binocular vision?
Stereopsis (depth perception).
Larger visual field.
“Spare” eye in case one is injured.
Binocular summation (stronger image from both eyes).
Enhanced space perception and hand-eye coordination.
What are the disadvantages or potential issues of binocular vision?
Complex neurophysiology required for fusion, which can cause eyestrain and headaches.
Problems with accommodation and convergence.
Stress from imbalanced refractive power (anisometropia) or retinal disease.
What is the role of the extraocular muscles (EOMs) in eye movement?
The EOMs control the movements of the eyes and are innervated by cranial nerves. These movements allow for primary, secondary, and tertiary eye positions.
Which cranial nerves innervate the extraocular muscles?
CN III (Oculomotor): Medial rectus (MR), Inferior oblique (IO), Superior rectus (SR), Inferior rectus (IR).
CN IV (Trochlear): Superior oblique (SO).
CN VI (Abducens): Lateral rectus (LR).
What is Sherrington’s Law of Reciprocal Innervation?
This law states that when an agonist muscle contracts, its antagonist muscle in the same eye relaxes proportionally (e.g., medial and lateral rectus muscles).
What is Hering’s Law of Equal Innervation?
This law states that the muscles of both eyes move equally when performing the same eye movement. The muscles involved are called “yoke muscles.”
What are the stages of binocular vision development according to Worth’s Classification?
Simultaneous perception and superimposition (1-3 months).
Fusion (~3 months).
Stereoscopic vision (3-5 months).
What is neonatal misalignment, and how is it characterized in infants?
Neonatal misalignment is common in infants and typically involves intermittent esotropia (inward turning of the eye). This is part of the developmental process.
What is the critical period for the development of binocular vision, and why is it important?
The critical period for binocular vision development is from around 4 months to 8-9 years. During this period, visual experience is crucial for normal development, and disturbances can lead to permanent vision issues.
What is amblyopia, and what are its classifications?
Amblyopia, also known as lazy eye, is reduced vision in one or both eyes. Its classifications include:
Stimulus deprivation amblyopia (monocular or binocular).
Strabismic amblyopia.
Anisometropic amblyopia.
Meridional amblyopia.
Ametropic amblyopia.
Occlusion amblyopia.
What is the main treatment approach for amblyopia?
Early intervention is essential. Treatments include refractive correction, occlusion therapy (patching), cycloplegic drugs, and computer-based therapies.
What is the prevalence of binocular vision problems in the UK, particularly in children?
By age 7, 2.3% of children have manifest strabismus.
3.6% of children have a history of amblyopia.
Hyperopic BV problems are more common in lower socio-economic groups.
What is the role of refractive balance in binocular vision?
An imbalanced refractive error, such as anisometropia (unequal refractive power between eyes), can cause problems with binocular fusion and lead to symptoms like eyestrain and diplopia.
What causes binocular stress?
Binocular stress can arise from:
Incorrect refractive balance.
Dissimilar images between the two eyes (e.g., anisometropia).
Conflict between accommodation and convergence.
What are the positions of gaze, and how are they classified?
Primary position: Straight ahead at a distant object.
Secondary position: Horizontal (left/right) and vertical (up/down) directions.
Tertiary position: Oblique (diagonal) movements of the eyes.
What are yoke muscle pairs in terms of eye movement?
oke muscle pairs are the muscles that work together for coordinated movement of both eyes in the same direction. For example, the right medial rectus (RMR) and left lateral rectus (LLR) are a yoke pair for leftward gaze.
What is the importance of sensory fusion and motor fusion in maintaining binocular vision?
Sensory fusion allows the brain to merge images from both eyes, creating a single, coherent perception. Motor fusion ensures that the eyes align properly to facilitate sensory fusion.
What are the common eye movement disorders associated with BV problems?
Strabismus: Misalignment of the eyes, which can result in diplopia.
Convergence insufficiency: Difficulty in focusing on near objects.
Stereopsis defects: Problems with depth perception.
Why are early treatments important for conditions like amblyopia?
Early treatment is crucial because the brain’s visual pathways are more flexible during the critical period, and early intervention can correct misalignments or refractive errors, preventing long-term visual impairment.
How does anisometropia affect binocular vision?
Anisometropia occurs when the two eyes have different refractive powers, causing unequal images between the eyes. This imbalance can disrupt fusion and lead to binocular vision problems such as amblyopia.
