ABV II Final Review

ABV II Final Review

• This review covers information for the ABV II final.
• Resources for further study are provided.
• Key topics include prism therapy types, prism positions, prism over specs, stacking prisms, primary vs. secondary deviations, prognostic guidelines, prism for intermittent strabs, prism for constant strabs, general guidelines, treatment of functional amblyopia, management of esotropia, management of exotropia, and management of vertical and non-comitant strabismus
• Important terminology, criteria, and considerations are included.
• Practice questions are provided to assess comprehension.

Prism Therapy Types

• Corrective (Neutralizing): Stabilizes normal sensory fusion by neutralizing demand for controlling fusional vergence.
• Relieving: Stabilizes normal sensory fusion by reducing demand for controlling fusional vergence, often to a level less than full correction.
• Overcorrective: Disrupts anomalous correspondence, forcing the system to look to a "new visual territory".

Prism Positions

• Prentice position (glass prisms): Placed parallel to the eyeball's direction.
• Frontal plane position (plastic prisms): Placed directly parallel to the target's plane.
• Minimum-deviation position (calibrated plastic prism): A calibrated position for accurate prism use.

Prism over Specs

• For exotropias (ETs), minus lenses create a BI effect.
• For esotropias (XT), minus lenses create a BO effect.
• The measured deviation will be larger than the true deviation with myopia and smaller than the true deviation with hyperopia.

Stacking Prisms

• The total power of two stacked prisms is greater than the sum of their individual prism powers.
• Combining prism with a Fresnel prism results in a greater power than the labeled powers.

Primary vs Secondary Deviations

• Non-Comitant:
  • Primary deviation: The unaffected eye fixates; prism is over the affected eye.
  • Secondary deviation: The affected eye fixates; prism is over the normal eye.
• Comitant: The angle of deviation is the same in all fields of gaze.

Prognostic Guidelines

• Early onset/long duration strabismus often presents as asymptomatic due to adaptations (suppression or anomalous correspondence).
• Must work on establishing normal sensory fusion before prism therapy.
• Recent onset/short duration strabismus presents as very symptomatic with no adaptations, so give prism.

Prism for Intermittent Strabs

• Prescribe the minimal amount of relieving prism to achieve single vision.

• Consider dissociated prism criteria based on percentage criteria of total deviation and vertical deviation.

  • Residual Vergence Demand Criteria: This must be known. Values for eso, hyper, and exo deviations are provided.

Prism for Constant Strabs

• Do not use prism if accommodating, AC is present, or if there is peripheral suppression or amblyopia.

General Guidelines for Prescribing Prism

• Avoid relieving or correcting prisms for AC patients - cosmetic prisms are acceptable.
• Carefully consider if relieving prism is appropriate when sensory fusion is present or binocularity can be sustained.
• Do not prescribe relieving or correcting prisms for accommodating patients unless cosmesis.
• Do not use vertical relieving prisms for secondary vertical or DVD.
• Place all, or most of the prism in the front of the paretic eye for nonconcomitant deviations.

Treatment of Functional Amblyopia

• Classifications include strabismic, anisometropic, isoametropic, and deprivation amblyopia.
• More favorable prognosis: anisometropic, hyperopic anisometropia, central fixation.
• Less favorable prognosis: strabismic, myopic anisometropia, and eccentric fixation.

Functional Amblyopia Management

• 3-step program (1) optical correction, (2) occlusion, (3) vision therapy.
• Treatment sequence: refractive correction, patching, and vision therapy.
• Active Amblyopia therapy: Form Recognition/Discrimination, Accommodation, Eye Movement and Fixation, Eye-Hand Coordination, and Binocular Therapy.

Treatment of Anomalous Correspondence

• Sensory Fusion: The process of combining stimuli from both eyes into a single perception.
• Motor Fusion: The relative movements of the two eyes in response to disparate retinal stimuli to obtain or maintain corresponding retinal areas needed to achieve single vision.
• Target Content and Position: Consider the stimulus for sensory and motor fusion separately.
• Target Content: Determined by target characteristics, in most cases, modification of the target is used to break down suppression and stimulate normal sensory fusion.
• Target Position: Stimulus to motor fusion depends on the strabismic angle.

Treatment

• Anti-suppression Therapy: Treatment done at the same time as sensorimotor treatment.
• Anti-suppression Treatment Goals:
  • Establish diplopia when strabismic.
  • Establish sensory fusion when aligned.
  • Stabilize sensory fusion if non-strabismic.

Anti-Suppression Instrument Selection

• Objective angle is used for constant strabismus.
• Slowly reduce the prism to help the patient achieve complete binocular vision in free space.
• Prescribe prism in the opposite direction of the intermittent turn for intermittent strabismus.

Suppression Breakers

• Techniques involve making the patient conscious of the suppression for adults, such as Fast Flashing, Blinking by Patient and Removal of Prism.

Anti-Suppression Training Techniques

• Techniques include visual activities for training patients with suppression.

Management of Esotropia

• Classifications: Divergence Insufficiency XT, Basic XT, and Divergence Excess.
• Prevalence and Signs and Symptoms: Most Intermittent XTs, Basic XTs, and Constant XTs (20-25%).
• Prognostic Factors: Frequency, Magnitude, Comitancy, Laterality, Age of onset, Duration

Management of Exotropia

• Classifications: Convergence Insufficiency XT, Basic XT, and Divergence Excess.
• Prevalence and Signs and Symptoms: Intermittent/Constant/Basic XTs.

Treatment Strategies (Exotropia)

• Motor Stimulation Method for IET and CET, surgical normalization of correspondence

Treatment Strategies (Esotropia)

• Motor Stimulation Method for IET and CET

Treatment Phases

• 1-4: Establish initial optical correction, improve monocular visual functioning, establish normal peripheral fusion, establish normal central and foveal vision.
• 5-6: Prescribe efficient binocular, active home maintenance program/re-evaluate.

VT Strategy for ET

• Obtain normal sensory fusion.
• Expand motor fusion ranges.
• Emphasize divergence.
• Increase quality of sensory responses.
• Improve fusional accuracy.

Considerations in Cases of Paresis

• Paresis can resolve, but sensory fusion can be disrupted.
• Consider HVT and occlusion therapy, as well as prisms and surgery if fusion isn't possible.

Other Non-Comitant Conditions

• Duane's Syndrome: Discuss seating arrangements if necessary, consider horizontal prism.
• Brown Syndrome, and Pattern Deviations: Appropriate treatment approach for the specific type and severity.

Pharmacological and Surgical Treatment

• Pharmacologic treatments for esotropia (Miotics)
• Surgical treatment, which is typically reserved for those cases that are not responding appropriately to other methods of treatment.

Cycloplegics and Penalization

• Near, Far, and Total penalization methods.

Chemodenervation

• Botox.

Surgical Treatment

• Surgical guidelines based on deviation magnitude for strabismus treatment.

Review Questions

• Review questions for assessment on the presented topics.