Idk Flashcards
(16 cards)
Define suppression
-Mental inhibition of visual sensations of one eye in favour of those of the other eye when both eyes are open.
- the process by which the brain inhibits the retinal image of one eye when both eyes are stimulatously stimulated.
-active cortical inhibition of unwanted stimuli
What are the suppression types
Pathological and permanent
suppression- ignore/inability to perceive image from both eyes at the same time
-psychological supression- ability to ignore images falling outside panums fusional space
What aspects of suppression can be investigated
-presence or absence of supression
-area and density of supression
-central or peripheral
-depth of supression
Lists the test which investigate suppression
-worth lights
-synotophore
-sbisa bar
-prisms
What is convergence
-it’s the nasal rotation of both eyes
-intersection of visual axis at a near point of regard
-inward movement of the visual axis
-it’s a type of disjunctive eye movement which is part of the vergence system
-can be voluntary
Identify the Components of Convergence (4 marks)
Tonic Convergence – Baseline convergence due to extraocular muscle tone.
Accommodative Convergence – Triggered by accommodation (linked via AC/A ratio).
Fusional Convergence – Fine motor adjustment to maintain single vision.
Proximal Convergence – Initiated by awareness of a near object.
What Units of Measurement Are Used to Measure Convergence?
uPrism dioptres and centimetres – clinical measurement
uDependent on IPD
Define Pseudo Strabismus
Pseudo strabismus is the false appearance of ocular misalignment, where the eyes appear turned (usually esotropic) despite being properly aligned. There is no true deviation.
List Causes of Pseudo Strabismus
Epicanthic folds – Skin folds covering the inner canthus.
Wide nasal bridge – Causes asymmetry in light reflex.
Telecanthus – Increased distance between inner canthi.
Asymmetrical palpebral fissures or facial features.
Define Angle Kappa with Reference to Positive and Negative Angle Kappa
Angle kappa is the angular difference between the visual axis (line from fovea to fixation point) and the pupillary axis (line perpendicular to cornea through the center of the pupil).
Positive angle kappa: Corneal light reflex appears nasal to the pupil center (common, may mimic exotropia).
Negative angle kappa: Corneal reflex appears temporal to the pupil center (less common, may mimic esotropia).
Name the four types of reflexive convergence
Tonic Convergence
Accommodative Convergence
Fusional (Disparity) Convergence
Proximal Convergence
: Define each type of reflexive convergence
Tonic Convergence – The baseline convergence tone due to tonic activity in the extraocular muscles when no visual stimulus is present (e.g., in darkness).
Accommodative Convergence – Convergence triggered by the effort to accommodate for near vision; measured using the AC/A ratio.
Fusional Convergence – A fine-tuning adjustment made to correct any disparity between the two retinal images to maintain single binocular vision.
Proximal Convergence – Convergence initiated by the awareness or perception of a near object, even before accommodation or disparity cues are active.
How is Near Point of Convergence (NPC) assessed in clinic
NPC is assessed by moving a fixation target slowly toward the patient’s nose along the midline and asking the patient to report when the image doubles (diplopia) or when the clinician observes a loss of convergence (eye drifts out).
The distance at which this occurs is measured in centimetres, and a typical NPC value is 5–10 cm.
Define Amblyopia
Amblyopia, also known as lazy eye, is a vision development disorder where one eye fails to achieve normal visual acuity, even with prescription glasses or contact lenses. It typically occurs when the brain favors one eye over the other, leading to reduced vision in the affected eye.
State the 3 components (including the time frame) of the critical period proposed by Daw
According to Daw (1998), the critical period for visual development has three phases:
Latent Period:
Birth to 6 weeks
The visual system is immature, and amblyopia is unlikely to develop despite abnormal input.
Sensitive Period:
6 weeks to 8 years
The visual cortex is highly plastic and vulnerable to abnormal input; amblyopia can develop during this phase.
Residual Plasticity Period:
8 years and beyond
Plasticity declines, but treatment may still lead to modest improvements.
Describe the different areas/changes along the visual pathway that have been proposed as possible primary sites involved in the aetiology of amblyopia (6–8 marks)
Retina:
Generally structurally normal; minimal retinal involvement in amblyopia, but some studies suggest subtle functional changes (e.g., reduced contrast sensitivity).
Lateral Geniculate Nucleus (LGN):
Amblyopic eyes show smaller LGN neurons and reduced neural activity in the layers corresponding to the deprived eye.
Primary Visual Cortex (V1):
Considered the main site of amblyopic deficits.
Features:
Reduced cortical representation of the amblyopic eye.
Abnormal binocular interaction (e.g., suppression and dominance of the fellow eye).
Impaired orientation and spatial frequency tuning.
Higher Visual Areas (e.g., V2, V4, MT):
Deficits may extend to higher-order visual processing areas, affecting motion perception, attention, and binocular integration.
Interhemispheric Connectivity:
Some evidence of altered communication between hemispheres due to disrupted visual input.
