Week 5 - Convergence anomalies Flashcards
What is convergence? Abnormality in this cause?
Convergence is a vergence movement that allows the visual axis to stay directed towards a near target.
An abnormality of convergence can result in the following:
• Convergence Insufficiency
• Convergence Paralysis
• Convergence Spasm
Near point of convergence (NPC) is the closest distance to which the eyes can converge while maintaining binocular single vision.
Differential Diagnosis
• Convergence Insufficiency or Paralysis
• Convergence Spasm
• Accommodation Insufficiency
• Accommodation Spasm
• Exophoria of convergence weakness type- exophoria 10^ near>distance
Convergence insufficiency
• Definition: Near point of convergence is less than 10cm.
- Convergence can only by maintained at this distance with effort.
• Can primary or secondary. Highly treatable.
• Primary: No other causes for convergence insufficiency are present, including heterophoria.
- Prevalence: 4.2%-17.6% in children
Aetiology of primary convergence insufficiency
Pre-disposing Factors:
• Large interpupillary distance
• Large periods of time only using distance fixation e.g., occupation
Precipitating Factors:
•Fatigue from long periods of close work with/without poor lighting
•Illness
•Age
•Medication/recreational drugs
• Pregnancy
Secondary Convergence Insufficiency causes
• Intermittent near exotropia
• Convergence weakness exophoria
• Neurological condition e.g., Parkinsons and horizontal gaze palsy
•Whiplash after road traffic accident
• Thyroid eye disease
• latrogenic- medial rectus weakness after surgery
Common symptoms:
•Patient often reports difficulty with reading or doing close work.
• Intermittent diplopia during near work.
• Blurred vision during near work.
• Frontal headache.
• Eyestrain.
• Difficulty concentrating.
• Movement of print.
Investigation
• Case History
• Distance and Near Vision
• Cover Test and Angle of Deviation
• Assessment of Convergence
• Accommodation
• Fusional Amplitude
Expand on:
Case History
Distance and Near Vision
Cover Test and Angle of Deviation
• Case History
- Ask about near work.
- Ask previous treatment- convergence insufficiency recurrent
• Distance and Near Vision
- Near vision may be reduced if associated accommodation insufficiency
• Cover Test and Angle of Deviation
- Investigation for exophoria- particularly at near. Important for appropriate diagnosis and management.
• Assessment of Convergence
• Accommodation
• Fusional Amplitude
• Accommodation
- Binocular accommodation may be reduced. Uniocular accommodation likely to be normal although associated accommodation insufficiency has been reported in some children.
• Fusional Amplitude
- Measured with prism bar in free space or synoptophore. Base out range may be reduced.
Assessment of convergence:
• Accurate assessment of convergence can be achieved by using the RAF rule.
• It allows for specific measurement of convergence and accommodation.
• It is equipment with near point of convergence measurements, diopters of accommodation and appropriate levels of accommodations based on patient’s age.
How to use the RAF:
• Ensure px wearing near correction
• Place RAF rule on px cheek, under lower lids
• RAF rule should be held slightly depressed
• Appropriate target should be selected for what being measured, start at 50cm
• Clear instructions should be given
• Px should be encouraged to maintain single vision
Recording results of RAF rule:
- All three measurements- not an average!
- If effort was exerted.
- If convergence was broken, which eye diverged.
- If the patient appreciated diplopia.
Example:
Binoc to 8cm, 10cm, 10cm c effort then LE diverges c diplopia
Treatment for a convergence insufficiency
Correction of Refractive Error
Orthoptic Exercises
Convergence Exercises:
• Smooth and Jump convergence
- Smooth convergence: Pen to nose exercises
- Jump convergence: Dot card
Base in Prisms:
Correct near exotropia
Convergence Paralysis types
The ability to converge is completely lost.
• May be primary or secondary.
• Primary:
- No previous history.
- Investigation rules out other secondary causes.
• Secondary:
- Head Trauma
- Neurological cause e.g, Parinauds syndrome, encephalitis, multiple sclerosis.
Clinical Features of Convergence
Paralysis
• Diplopia for all distances nearer than infinity.
- Exotropia at near.
• Ocular motility is normal in primary convergence paralysis.
• Accommodation may or not be impacted.
