Alternating Strabismus: Effects and Adaptations

Definition of Strabismus

• Strabismus, commonly known as eye misalignment, is when the eyes fail to align properly when focusing.
• Normal vision involves parallel eyes working together to produce a single, clear, three-dimensional image.
• In strabismus, synchronized function is disrupted, causing one eye to deviate while the other remains fixed and can occur inward (esotropia), outward (exotropia), upward (hypertropia), or downward (hypotropia).

Further Details on Eye Misalignment

• Constant deviation indicates a persistent muscle or nerve issue.
• Intermittent strabismus surfaces during fatigue, illness, or visual stress, often seen in exotropia cases when viewing distant objects.
• Unilateral strabismus consistently affects the same eye, potentially leading to amblyopia (lazy eye).
• Alternating strabismus shifts the deviation between both eyes, reducing the risk of amblyopia but impairs binocular vision and coordination.

Impact of Strabismus on Visual Function

• Misaligned eyes send two different images to the brain preventing the images to merge (fusion).
• Adults experience double vision (diplopia), making visual tasks challenging.
• Children's brains suppress the image from the misaligned eye to reduce confusion, potentially leading to amblyopia.
• Amblyopia occurs when the visual cortex stops processing input from the deviating eye, resulting in permanently reduced vision if not corrected early.

Underlying Causes of Strabismus

• Six extraocular muscles control eye movement and alignment, dysfunction causes deviations in one or more directions.
• Overaction or tightness of the medial rectus muscle causes esotropia, while weakness in the lateral rectus muscle causes exotropia.
• Cranial nerve disorders: Eye muscle function relies on three cranial nerves (Oculomotor, Trochlear, Abducens).
• Damage to these nerves from trauma, stroke, tumors, or systemic diseases results in paralytic strabismus.
• Significant farsightedness (hyperopia) forces excessive focusing, which can trigger accommodative esotropia, a common type in children.
• Neurological conditions like cerebral palsy, Down syndrome, and brain injuries can interfere with eye muscle coordination.
• Systemic diseases like diabetes may cause cranial nerve palsies leading to eye misalignment.

Impact on Visual Function and Quality of Life:

• Untreated strabismus in children can lead to developmental delays in visual processing, motor skills, and hand-eye coordination.
• Poor depth perception and limited peripheral vision hinder activities like sports or reading.
• Social and psychological effects are significant due to visible misalignment.
• Sudden-onset strabismus in adults causes functional limitations due to double vision, making tasks like reading and driving difficult.
• Patients experience dizziness, headaches, and visual fatigue, significantly impairing their quality of life.
• Compensatory head tilting or turning is often observed to reduce visual strain or diplopia.
• Strabismus is a complex condition requiring prompt treatment to preserve functional vision and improve quality of life.

Classification and Differences Between Heterophoria and Heterotropia in Strabismus

• Heterophoria (Latent Strabismus): Latent eye misalignment that remains controlled by the brain's fusion mechanism under normal conditions. It only becomes noticeable when fusion is disrupted, such as during monocular viewing (e.g., when one eye is covered).
• Can be Esophoria, Exophoria, Hyperphoria, and Hypophoria.
• Often asymptomatic but may cause eye strain, headaches, and intermittent double vision during visual fatigue, prolonged near tasks, or reading.
• Detected with the Cover-Uncover Test or Alternate Cover Test, measured using prisms or the Maddox Rod Test.
• Correct refractive errors with glasses and reduce symptoms.
• Perform vision therapy strengthens fusion and binocular stability. Heterotropia (Manifest Strabismus):
• Visible misalignment of the eyes occurs when the brain's fusion mechanism fails to control ocular alignment.
• The deviation is constant or intermittent, even when both eyes are open.
• Types include Esotropia, Exotropia, Hypertropia, and Hypotropia.
• In children, it includes risk of amblyopia from suppression and double vision.
• In Adults, it includes Double vision , eye strain, or abnormal head posture minimizes symptoms, loss of binocular vision and depth perception.
• Measured using the Cover Test, Krimsky Test with prisms, and ocular motility testing; sensory adaptations via Synoptophore.
• Correct refractive errors and use patching therapy for amblyopia, prisms for symptom relief, and surgery for significant deviations.
• Implement vision therapy improves eye coordination and binocular function.

Types and Diagnosis of Strabismus Based on the Direction of Deviation

• Esotropia (inward turning of the eye): constant or intermittent.
• Accommodative occurs due to uncorrected hyperopia, causing overfocusing and eye crossing.
• Exotropia (outward turning of the eye) is noticeable when tired or daydreaming, possibly becoming constant without treatment.
• Hypertropia and Hypotropia are vertical misalignments with the eye turning upward or downward, often caused by superior oblique palsy or trauma.
• Can cause significant diplopia

Based on the Cause (Etiology)

• Accommodative Esotropia: occurs primarily due to excessive accommodation triggered by hyperopia.
• Refractive Accommodative Esotropia: Seen in patients with moderate to high uncorrected hyperopia (typically +2.00 D to +6.00 D).
• Excessive accommodation induces excessive convergence, resulting in inward eye deviation.
• It usually manifests between 2-3 years, gradual onset, and intermittent at first, can include eyestrain, blurred vision, and intermittent diplopia, particularly during near tasks. Optical correction w/ glasses reduces accommodative demand and prevents convergence excess.
• High AC/A Ratio Accommodative Esotropia: High AC/A results in excessive convergence even with minimal accommodation effort
• More prominent during near fixation.
• Bifocal/progressive addition lenses reduce near-point accommodative demand.
• Sensory Strabismus: Vision loss/poor sensory fusion in one eye leads to secondary strabismus.
• Can be caused by Congenital cataracts, optic nerve hypoplasia, retinal disease, or anisometropia.

Common Types

• Sensory esotropia or exotropia, depending on age of onset.
• Consecutive Strabismus: post-surgical/traumatic change reverses initial deviation into another direction.
• Management: Wait-and-see for small angles; prisms or surgery for deviations
• Paralytic Strabismus: nerve palsy with extraocular muscles.

Paralytic Strabismus Unique Insights

• Cranial nerve III palsy causes ptosis, outward deviation, and pupil dilation.
• Cranial nerve VI palsy affects lateral rectus function.

Based on the Magnitude of Deviation

• Microtropia: A small-angle & unnoticed form, with minimal misalignment, reduced stereopsis (depth perception), and visual suppression in misaligned eye.
• Despite small angle, microtropia may cause amblyopia and reduced binocular function.
• Large-angle Strabismus: Noticeable and measurable eye misalignment above 20 prism diopters, if untreated it can cause, amblyopia in children, diplopia in older children/adults, reduced vison, or eye strain

Calculation of the AC/A Ratio

• The relative amount of a gradient Method: used to determine the accommodative convergence.
• Formula: AC/A = (Deviation w/o lens - Deviation w/ lens)/ Lens Power
• Calculated Method: Use the interpupillary distance (IPD).
• Formula: AC/A = IPD +( near deviation-distance deviation from near distance)

When to Calculate the AC/A Ratio

• Useful in diagnosing high AC/A accommodative esotropia and other strabismus conditions with near challenges, helps distinguish btwn the condition.
• Clinical Benefit: Determines Role of optics to guide correct usage of vision, and help patients avoid risky work, like excessive convergence

Strabismus Classification by Vertical Gaze

• Classifications are A and V patterns: include 1. A-Pattern Strabismus when the deviations occur in the gaze of down and decrease.
• Can increase or decrease gaze
• V Patterns: increase in down and decrease in gaze.

Primary Comitant Esotropia

• Deviation in fixation and equal gaze.
• Comitants can classify if there is equal gaze.
• Primary Classifications is either being Basic where deviation is equal for distance or a divergence that is insufficient.

Prescribing Glasses for Myopia/Hyperopia

• 1. Hyperopia Esotropia: Hyperopia worsens convergence and accommodation.
• 2. Myopia Esotropia: Minimal impact.
• Optimal vision Prescriptions
• 3. Myopia Worsens reduced accommodation for weakening converges, worse prescriptions help improve better alignment.
• A Slight adjustment can help increase alignment
• 4. Hyperopia Exotropia: Convergence can lead to reduced convergence where prescriptions should be set lower, lenses can increase convergence

Diagnostic Methods for Strabismus

• Hirschberg Test (Corneal Light Reflex Test): It's simple for testing and diagnosing of severity. A light is directed at cornea and reflex position evaluated if you can view any displacement
• Krimsky Test: Bar that is focused on the ocular, prism is focused when viewing, light is centered
• Alternate Test: Measuring Tropia that are covered by phorias that are covered over a target in far/near distances. With movement, uncovering is tested.
• Cycloplegic refraction is preformed for refractive levels particularly in accommodated test settings. Eye drops are used to temporarily paralysis the ciliary accommodation by testing eye movements.

Diagnostic Method Purpose

• Evaluates position of eye muscle during up down movement when neurology is required. The functions are determined if suspected to be under neurological reasons.
• Neurology test help assess where alignment is.

Maddox Rod Test General Info

• A simple diagnostic procedure for latent issues. During a test, the patient is asked to stare at fixed light while tests occurs. Vertically it assesses torsion differences.

Prism Testing General Info

• Prism is alternated with the amount of deviation . The difference that occurs is from the cover. Strength measures angles needed for vision. Needed for surgical procedures.

Synoptophore(Major Amblyoscope) General Info

• A specified instrument used to evaluate. Fusion and suppression of each visual sensory field. Used for detecting the abnormalities.

Basic Tests - General Summary

• These (Krimskj and Cover) measure the misalignment. Refractory test. And muscle testing to view alignment and neurology levels.

Basic Treatments

• (Not surgical) Includes glasses ,contact lens( for accommodative esotropia). Bifocals are set closer.
• Prim lens; helps reduce displacement to allow compensation.
• Vision therapy also works with convergence and function
• For intermittent vision
• Injections; paralysis's overacting muscles for the weakened eye.
• This is for paralytic situations.

Surgical Treatments

• Recession Surgery: reduces overacting and sclera levels. resections surgery strengthens those muscles and sutures for precise alignment. And vertical alignment.

Post Treatment Care

• Follow ups ensure and detect residual amblyopia.
• Therapy for binocular vision in surgery for cases that may result in re-occurring issues.

Low Vision

• WHO definition: Low vision is defined as a condition where the patient with better eye is 6/18 to 3/60, even with the best correction
• Characteristics: Affects simple daily vision where patients need assistive devices.

Vision Loss and Assistive Devices

• Normal Vision: Acuity between (V.A): 6/6-6/12. Tasks are normally accomplished .
• Visual Impairment: <6/12 -6/18 with dim setting adjustments. Moderate Impairments: Difficulty with daily function, V.A btwn <6/18:6/60
• Severe vision ( V.A ) is bad and difficult w/ tasks to perform Blindness: Defined: V.A <36/60 degrees V.A or when individuals can't perform a light/residual function

Instruments and Devices Used for Low Vision

• includes optical & non optics devices
• Spectacle: (High Powered Lenses). (Hands Free) used for handheld devices.
• Magnifiers: Allow illuminated versions with stands to view stable view.
• Non Optics: Large Print/ Aids where light decreases sensitivity

Assistive Devices and Software

• Electronics is for smart apps.
• Reading aids.
• Audio: For contrast on audio books

Testing for Low Vision (Vision Acuity)

Tests for low vision testing range in levels

• General viewing w patients can't view (LogMAR/ NEAR)
• Refraction: test of sight/autorefractory test/
• contrast (vision impairments). Poor foggy condition.

Visual Field

• Measures visual field to determine. Conditions related to light. It is assessed by measuring eye views. To increase visual by either adding objects ,or increase size like enlarged bold.
• Magnifiers where glasses telescope for increase distance.
• Optical aids: High powered lenses to test. Handheld devices for close up work.
• And stable hand controls devices.

Explore alternating strabismus, its impact on binocular vision, and the brain's adaptive mechanisms. Understand why binocular vision is impaired and how the brain suppresses images to cope with misaligned eyes. Learn about potential consequences and therapeutic approaches.