LEARN ASAP Flashcards
(21 cards)
Define amblyopia
amblyopia is defined as a reduction in visual acuity in one (or sometimes both) eyes that cannot be corrected by refractive means and is not due to any structural abnormality of the eye or visual pathway.
A condition of diminished visual form sense,
classify amblyopia stating the nature of the defect for each type
Strabismic amblyopia- due to a presence of manifest strabismus.
How: results in distruption of visual form sense-results in va reduced in one eye
Ammetropic- bilateral due to high uncorrected refractive error
How- distruption of visual form sense due to blurred images on retina
Stimulus deprivation- as a results of inadequate visual stimuli
How- distruption of light and visual form sense
Anismotrippic- significant difference in refractive error between each eye.
How-disruption of visual form sense due to unequal blurred images on the retina
State the factors that may affect the prognosis of amblyopia
Age when treatment starts
Type of amblyopia
Duration of visual deprivation
Depth of amblyopia
Treatment compliance
Define 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
Convergence can be divided into voluntary and reflexive. Name the four types of reflexive convergence (4 marks) and define each (4 marks).
Tonic convergence- responsible for bringing eyes into primary position.
It is brought about by the muscle tone of extraocular muscles
Proximity convergence- induced by being aware of nearness of an object. The object could either be placed at Near vision distance or an image of an object, optically placed at far distance, but at close proximally for example, a synoptophore
Fusional convergence-A fine-tuning adjustment made to correct any disparity between the two retinal images to maintain single binocular vision.
Accomadative- Convergence triggered by the effort to accommodate for near vision; measured using the AC/A ratio.
What is pseudo strabismus (2 marks)? List the causes of pseudo strabismus (4 marks).
Pseudo strabismus is the False appearance of a strabismus under binocular viewing conditions. despite being properly aligned. There is no true deviation.
Epicanthic folds - Skin folds covering the inner canthus.
Wide nasal bridge - Causes asymmetry in light reflex.
Belpharophimosis- reduced lid size
Telecanthus - Increased distance between inner canthi.
Asymmetrical palpebral fissures or facial features.
Abnormality of lid positions
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).
A positive angle kappa is where the optical axis cuts the posterior pole of the globe nasally and inferior to the fovea and therefore the CR will appear slight nasal to the pupil centre giving rise to a pseudo-exotropia
Negative angle kappa: Corneal reflex appears temporal to the pupil center (less common, may mimic esotropia).
Abnormal correspondence
•A change in visual projection.
•The fovea of the fixing eye has a common visual direction with an area other than the fovea of the deviating eye.
•The pairing of all retinal areas is changed
Types of ac
Types of AC
•Harmonious AC
• angle of anomaly = the objective angle
(distance from the fovea to the extra foveal point in the deviating eye = the angle of strabismus)
•Subjective angle is 0
•Unharmonious AC
•Angle of anomaly differs from the objective and subjective angle
•The brain uses a point between the fovea and the full angle of deviation to correspond with the fovea.
•Rare – possibly an anomaly of testing
Deviations most likely to develop arc
Size of deviation?
•Usually angle less than 20 prism diopters
•Brain develops chains of neurons to link ocular dominance columns
•This is easier with smaller deviations as the distance between relevant ocular dominance columns are smaller
Type of deviation?
•Constant strabismus, usually esotropia
Name 4 tests that can be used to investigate abnormal correspondence (4 marks)
Bagolini Striated Lenses Test
Worth Four Dot Test
After-Image Test
Synoptophore Test
Supression
-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
Tests used to measure supression
-worth lights
-synotophore
-sbisa bar
-prisms
What elements of suppression can be assessed clinically and what do you understand by these terms? (4 marks)
Presence – Whether suppression is occurring or not. Clinicians use tests like the Worth 4 Dot test or Bagolini lenses to determine if one eye’s image is being ignored.
Depth – How strongly the suppression is occurring. Deep suppression indicates the eye is almost completely ignored, even under binocular viewing, while shallow suppression may only occur in specific situations.
Size (Area) – The extent or area of the visual field affected by suppression. This can be mapped using tests like the synoptophore.
Location – Whether suppression occurs centrally (at the fovea) or peripherally, which can influence the management strategy.
Muscle sequalae
The process of EOM muscle underactions and overactions as a result of a primary muscle weakness/inability to move fully
Daws law
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.
ACA DEFINITION
The AC/A (Accommodative Convergence to
Accommodation) ratio describes the
relationship between the amount of convergence (in prism dioptres) induced per dioptre of accommodation. It indicates how much a patient’s eyes converge in response to focusing (accommodation) for near tasks.
Modification of AC/A Ratio
Corrective lenses: Plus lenses reduce accommodation, thereby reducing accommodative convergence.
Prism therapy: Alters fusional vergence demand, potentially influencing AC/A dynamics.
Vision therapy/orthoptics: Can train the visual system to improve control of accommodation and vergence.
Surgical intervention: In some strabismus cases, surgery can alter muscle function, indirectly affecting AC/A effects.
Tests
Cover test, PCT, PFR, NPC, PFR, synotophore
Muscle sequale
Muscle Sequelae
1.Underaction of the affected muscle
2.Overaction of the contralateral synergist (Hering’s law of equal innervation)
3.Contracture of the ipsilateral antagonist (Sherringtons’s law of reciprocal innervation)
4.Secondary inhibition of the contralateral antagonist (Hering’s law of equal innervation) which occurs due to the contracted antagonist in the affected eye requiring less innervation.
