Lesson Summary

When managing a patient with double vision, it is essential to consider various treatment options, with prism being a primary intervention. Here is a detailed overview of prism usage, benefits, risks, and complementary treatments.

Benefits of Prism:

• Alleviates double vision quickly, especially in acute cases.
• Enhances binocular vision when the eyes can still work together.
• Improves quality of life and stabilizes vision.
• Non-invasive approach.

Considerations and Risks:

• Risk of prism adaptation, particularly with base-out prism, leading to dependency.
• Prismdemand can increase, complicating future treatments like contact lens use.
• Prism moves the image toward the apex, with base-out shifting image inward and base-in expanding visual space outward.
• Yoked prism (same base direction in both eyes) can be used, including vertical (base-up or base-down) and horizontal orientations, influencing perception in a 3D way.

Prescribing Prism - Five Key Tips:

1. Measure alignment: Use unilateral and alternating cover tests and tools like phoropters in various head positions.
2. Determine lowest effective prism: Start with small amounts (e.g., 0.5 to 1 prism diopter) to reduce symptoms rather than strictly aiming for orthophoria.
3. Recheck findings after trial: Assess changes in near point of convergence or other clinical signs after applying prism in trial frames.
4. Prescribe appropriately: Apply prism in the relevant prescription (distance or near) depending on when symptoms occur.
5. Monitor closely: Follow up about a month after fitting to evaluate symptom improvement and prevent overprescription.

Types of Prism:

• Fresnel prism: Quick, temporary relief, ideal for acute cases; less optical quality and more visible on lenses.
• Ground-in prism: Used for stable, long-term double vision; allows small precise powers and better optical quality.

Strategies to Avoid Prism Adaptation:

• Prefer base-down prism over base-out when possible to avoid increased prism demands.
• Consider alternatives like narrow binasal occlusion and vision hygiene.
• Educate patients on visual rest breaks, relaxation, and vision therapy.

Additional Treatment Options Beyond Prism:

• Lenses: Small plus lenses may reduce eye strain and help with near-point triad issues; useful for both esophoria and exophoria.
• Binasal Occlusion: Blocks the nasal part of the lenses to reduce image overlap and ease binocular fusion, especially helpful in brain injury patients.
• Vision Therapy: Crucial for rehabilitation, often combined with prism or lenses to improve binocular function.
• Strabismus Surgery: Only recommended if the double vision is consistent, long-standing, constant, and comitant (similar in all gaze directions). Surgery is usually followed by vision therapy for best outcomes.

Summary:

• Start with the lowest effective prism power that improves comfort and symptoms.
• Regular assessments and patient monitoring are critical to avoid overprescription and adaptation.
• Consider multiple modalities—prism, lenses, binasal occlusion, vision therapy—tailoring treatment to individual patient needs.
• Surgery is a last resort under specific criteria, and post-operative rehabilitation is important.