Strabismus Flashcards
What is strabismus?
Misalignment of the visual axes of the two eyes.
Define binocular single vision (BSV).
The ability to view an object with two eyes, forming two separate images and fusing them centrally into one perception with depth.
What is the difference between heterophoria and heterotropia?
Heterophoria is a latent deviation kept latent by fusion reflex, while heterotropia is a manifest deviation where visual axes do not intersect at the fixation point.
What is concomitant squint?
A type of manifest squint with constant deviation in all gaze directions and no limitation of ocular movements.
What distinguishes incomitant squint from concomitant squint?
Incomitant squint has varying deviation in different gaze directions and could be paralytic, paretic, or restrictive.
Name the primary action of the medial rectus muscle.
Adduction.
Which nerve innervates the lateral rectus muscle?
The abducent nerve (CN VI).
What is the primary action of the superior rectus muscle?
Elevation, maximal when the eye is abducted.
What are the subsidiary actions of the inferior rectus muscle?
Adduction and extortion.
How does superior oblique action differ when the eye is adducted?
It causes depression and abduction, with depression maximal when the eye is adducted.
Define versions in terms of eye movement.
Binocular, simultaneous conjugate eye movement in the same direction.
List the six cardinal positions of gaze.
Dextroversion, laevoversion, dextroelevation, dextrodepression, laevoelevation, laevodepression.
What is the significance of the nine diagnostic positions of gaze?
They help measure deviations in different gaze positions for accurate diagnosis.
What sensory adaptation mechanisms occur with strabismus?
Sensory adaptation includes suppression and abnormal retinal correspondence.
What is the role of suppression in sensory adaptation?
Suppression is a sensory adaptation where the brain ignores the image from the deviated eye to avoid double vision.
Describe motor adaptations that occur in strabismus.
Face turn, head tilt, chin elevation, or depression.
What are the key factors in the aetiology of heterophoria?
Orbital asymmetry, abnormal interpupillary distance, and dissociation factors like monocular tasks.
How can uncorrected refractive error lead to concomitant strabismus?
It disrupts accommodation and convergence mechanisms, leading to misalignment.
Name a neurogenic cause of incomitant strabismus.
Congenital hypoplasia or aplasia of cranial nerves III, IV, or VI.
How does myasthenia gravis affect ocular muscles in strabismus?
Myasthenia gravis causes weakness in the neuromuscular junction, leading to eye muscle weakness and strabismus.
What are key points to assess in the history of a patient with strabismus?
Age of onset, variability, direction of deviation, precipitating factors, and family history of strabismus.
What is the cover/uncover test used to confirm?
A manifest squint or misalignment.
What are the weakening surgical procedures for treating strabismus?
Recession, disinsertion, myotomy, myectomy.
What are the strengthening surgical procedures for treating strabismus?
Resection, advancement, tucking.
Name an inflammatory lesion that can cause neurogenic incomitant strabismus.
Encephalitis or meningitis.
How can face turn be a motor adaptation to strabismus?
It helps the patient avoid diplopia by aligning the eyes to reduce the deviation.
Why is early detection of strabismus important in children?
Early detection prevents the development of amblyopia and permanent vision problems.
Describe the role of prisms in the treatment of strabismus.
Prisms help realign light entering the eye, aiding in visual fusion.
What condition is often treated using botulinum toxin injections in strabismus?
Paralytic strabismus or transient squints.
What role does orthoptic exercise play in the management of convergence insufficiency?
It strengthens weak eye muscles, improving binocular vision and alignment.
