Exodeviations Cheatsheet

Cheatsheet Content

### Introduction to Exodeviations Exodeviations are a type of strabismus (eye misalignment) where one or both eyes turn outward. This is often referred to as "walleye." Understanding exodeviations is crucial for optometrists and ophthalmologists as they can impact binocular vision, depth perception, and lead to asthenopia (eye strain). ### Classification of Exodeviations Exodeviations are classified based on their presentation, frequency, and underlying mechanism. #### A. By Frequency - **Intermittent Exodeviation (IXT):** The most common type. Deviation is present sometimes (e.g., when tired, daydreaming, or looking in the distance) but eyes are straight at other times. - **Constant Exodeviation (CXT):** Deviation is always present. This has a higher risk of developing amblyopia (lazy eye) or suppression. #### B. By Distance - **Basic Exodeviation:** Deviation is roughly equal for both near and distance vision. - **Divergence Excess (DE):** Deviation is significantly greater at distance than at near (difference usually >10 prism diopters, PD). - **Convergence Insufficiency (CI):** Deviation is significantly greater at near than at distance (difference usually >10 PD). Patients often complain of eye strain, headaches, and diplopia (double vision) when reading. #### C. By Fixation Preference - **Alternating Exodeviation:** Eyes take turns deviating. This usually indicates good visual acuity in both eyes. - **Unilateral Exodeviation:** One eye consistently deviates. This often suggests amblyopia or poorer vision in the deviating eye. #### D. Special Types - **Simulated Divergence Excess:** Appears like DE, but after patching one eye for 30-60 minutes (to disrupt fusional convergence), the near deviation increases to match the distance deviation. This indicates an underlying basic exodeviation masked by tonic convergence. - **Pseudo-exodeviation:** Eyes appear to turn out, but are actually straight. This can be due to a wide interpupillary distance, positive angle kappa, or temporal displacement of the fovea. ### Key Terms - **Suppression:** The brain ignores the image from one eye to avoid diplopia. - **Amblyopia:** Reduced vision in an eye that did not develop normal sight during childhood. - **Diplopia:** Double vision. - **Asthenopia:** Eye strain, fatigue, or discomfort. - **Prism Diopter (PD):** Unit of measurement for eye deviation. ### Diagnosis of Exodeviations A thorough eye examination is essential. #### A. History Taking - Onset (congenital, acquired) - Frequency (constant, intermittent) - Symptoms (diplopia, asthenopia, blurred vision, headaches) - Precipitating factors (fatigue, illness, distance viewing) - Family history of strabismus #### B. Clinical Tests 1. **Visual Acuity:** Assess for amblyopia. 2. **Refraction:** Correct significant refractive errors, especially hyperopia or astigmatism. 3. **Cover-Uncover Test:** Identifies phorias (latent deviations) and tropias (manifest deviations). - **Exophoria (XP):** Latent outward deviation. Eye drifts out when covered, then recovers when uncovered. - **Exotropia (XT):** Manifest outward deviation. Eye is visibly turned out. 4. **Alternate Cover Test:** Measures the full amount of deviation at both near (33cm) and distance (6m) using prisms. 5. **Ocular Motility:** Assess eye movements (versions and ductions) for restrictions or overactions. 6. **Stereopsis (Depth Perception):** Often reduced or absent in constant exotropia, may be intermittent in IXT. 7. **Fundus Examination:** Rule out underlying pathology. 8. **Angle Kappa:** Measurement of the angle between the pupillary axis and the visual axis. A positive angle kappa can give the appearance of exodeviation. ### Management of Exodeviations Treatment aims to achieve comfortable, single binocular vision, preserve visual acuity, and improve cosmetic appearance. #### A. Non-Surgical Management (Often First-Line for Intermittent Exodeviations) 1. **Refractive Correction:** Correcting significant refractive errors can sometimes improve control of the deviation. 2. **Vision Therapy (Orthoptics):** - **Pencil Push-ups:** Improves convergence ability for CI. - **Brock String:** Enhances fusional awareness and convergence. - **Stereograms/Anaglyphs:** Improves stereopsis and fusional reserves. - **Computerized Vision Therapy:** Engages patients with interactive exercises. - **Goal:** Improve fusional convergence amplitude and control to keep eyes aligned. 3. **Prism Lenses:** - **Base-in prisms:** Can be prescribed to reduce the visual demand on convergence, helping to alleviate symptoms like diplopia and asthenopia, especially for CI. - **Relieving prisms:** Used to treat symptoms, not to cure the deviation. 4. **Over-minus Lenses:** - Prescribing slightly more minus power than needed (e.g., -0.75D to -2.00D) can stimulate accommodative convergence, thereby reducing an exodeviation, especially in DE. More commonly used in children. 5. **Patching/Occlusion:** - **Full-time patching:** For amblyopia treatment. - **Alternate patching:** Can be used to disrupt suppression and encourage alternate fixation. - **Part-time patching:** For intermittent exotropia, can sometimes improve control. 6. **Observation:** For very small, asymptomatic exophorias, or intermittent exodeviations with good control and no symptoms, observation may be appropriate. #### B. Surgical Management (When Non-Surgical Fails or Deviation is Large/Constant) - **Indications for Surgery:** - Large, constant exotropia. - Intermittent exotropia that is poorly controlled, causing significant symptoms (diplopia, asthenopia) or progressive increase in frequency/magnitude. - Amblyopia that persists despite patching and refractive correction. - Significant cosmetic concern. - **Types of Surgical Procedures:** 1. **Lateral Rectus Recession (Weakening Procedure):** The lateral rectus muscle (which pulls the eye outward) is detached from its insertion point and reattached further back on the sclera. This weakens its pulling effect. - **Bilateral Lateral Rectus Recession (BLR):** Performed on both eyes, common for basic exotropia and divergence excess. 2. **Medial Rectus Resection (Strengthening Procedure):** A portion of the medial rectus muscle (which pulls the eye inward) is removed, and the muscle is reattached at its original insertion point. This shortens and strengthens the muscle. - **Unilateral Recession/Resection (R&R):** Lateral rectus recession in one eye and medial rectus resection in the same eye. Used for unilateral exotropia. - **Medial Rectus Resection (MRR):** For convergence insufficiency type exodeviation. Can be combined with lateral rectus recession. - **Post-operative Care:** - Eye drops (antibiotics, steroids). - Follow-up examinations to monitor alignment and vision. - Vision therapy may still be beneficial post-surgery to refine binocular function. ### Prognosis - **Intermittent Exotropia:** Good prognosis with appropriate management. Many can maintain good binocular function. - **Constant Exotropia:** Higher risk of amblyopia and suppression, often requires earlier and more aggressive intervention. - **Convergence Insufficiency:** Responds well to vision therapy. ### Summary Exodeviations are a spectrum of outward eye misalignments. Accurate classification based on frequency, distance, and underlying mechanisms is crucial for guiding management. While non-surgical approaches like vision therapy and prisms are often effective, especially for intermittent types, surgical intervention may be necessary for larger, constant deviations or when conservative treatments fail. Early diagnosis and intervention are key to preserving binocular vision and preventing long-term complications.