Introduction

Retinitis pigmentosa affects approximately 1 in 4,000 individuals worldwide, making it one of the most common inherited retinal diseases. The condition typically manifests with night blindness and progressive visual field constriction, eventually affecting central vision in advanced stages.

Pathophysiology

Genetic Basis

RP can be inherited in autosomal dominant, autosomal recessive, or X-linked patterns, with over 100 genes identified as causative factors. The most commonly affected genes include:

- RHO (rhodopsin)

- USH2A (usherin)

- RPGR (retinitis pigmentosa GTPase regulator)

Disease Progression

The hallmark of RP is the primary degeneration of rod photoreceptors, followed by cone deterioration. This sequential loss explains the characteristic progression of symptoms:

1. Night blindness (nyctalopia)

2. Peripheral visual field loss

3. Tunnel vision

4. Central vision deterioration

Diagnostic Methods

Electroretinogram (ERG)

The ERG is a crucial diagnostic tool in RP assessment and monitoring. It measures the electrical responses of various cell types in the retina, including:

Standard ERG Components

- Scotopic Response: Measures rod function in dark-adapted conditions

- Photopic Response: Evaluates cone function in light-adapted conditions

- Mixed Response: Assesses combined rod-cone function

ERG Patterns in RP

- Early Stage: Reduced scotopic b-wave amplitude

- Mid Stage: Diminished scotopic and photopic responses

- Advanced Stage: Often non-recordable or severely attenuated responses

Clinical Significance

- Early Detection: ERG can detect retinal dysfunction before visible symptoms

- Disease Monitoring: Helps track progression rate

- Prognostic Value: Assists in predicting disease course

- Genetic Correlation: Different ERG patterns may suggest specific genetic variants

Orthoptic Assessment and Management

Specialized RP Assessment Protocol

• Goldmann Visual Field perimetry (preferred over automated perimetry due to better reliability in RP)

• Preferential Looking Tests for early-onset cases

• Dark Adaptometry

• Full-field ERG and multifocal ERG

• Contrast sensitivity using Pelli-Robson charts

• Reading speed assessment with MNRead or IReST texts

Evidence-Based Orthoptic Interventions

1. Eccentric Viewing Training (EVT)

Specific protocols for RP patients:

• Identification of the Preferred Retinal Locus (PRL)

• Ring scotoma-specific adaptation exercises

• Training sequence:

  • Static letter identification

  • Dynamic text tracking

  • Real-world scene analysis

2. Peripheral Field Awareness Training

RP-specific approaches:

• Reverse Telescope Training (RTT) for field expansion

• Compensatory scanning patterns for ring scotomas

• Zeitgeist field awareness exercises

• Visual search training with specific emphasis on the remaining peripheral field

3. Low Vision Rehabilitation Specific to RP

• Prescribed optical devices:

  • High-addition bifocals for ring scotoma

  • Reverse telescopes (2x to 4x) for field awareness

  • Selective transmission filters (especially 550nm)

• Non-optical devices:

  • Modified lighting techniques accounting for photophobia

  • Specific smartphone/tablet adaptations for RP users

Measurable Outcomes and Monitoring

Standardized assessment tools for RP:

• NEI-VFQ-25 scores

• Activity Inventory (AI) measurements

• Manchester Low Vision Questionnaire (MLVQ)

• Documented visual field progression

• Reading speed and accuracy metrics

• Mobility assessment scores

Disease-Stage Specific Interventions

Early Stage

• Dark adaptation training

• Initial peripheral awareness exercises

• Preventive scanning training

Mid Stage

• Intensive EVT

• Ring scotoma management

• Combined optical device training

Advanced Stage

• PRL refinement

• Mobility-focused training

• Sensory substitution introduction

Contraindications and Precautions

• Avoidance of prolonged near work without breaks

• Modified approach for patients with concurrent macular edema

• Careful monitoring of photophobia during training

• Adaptation of exercises for patients with associated systemic conditions

Evidence-Based Outcomes

Recent studies demonstrate:

• 60% improvement in reading speed with specialized EVT

• 40% increase in visual search efficiency

• Significant improvement in quality of life measures

• Maintained functional independence for extended periods

Clinical Outcomes

Research indicates that early orthoptic intervention can:

- Improve functional vision utilization

- Enhance quality of life

- Maintain independence longer

- Slow the perceived impact of vision loss

Conclusion

Orthoptic management plays a crucial role in maintaining functional vision and quality of life for individuals with RP. A comprehensive approach combining traditional orthoptic techniques with modern technological innovations offers the best outcomes for patients. The integration of ERG testing provides crucial objective data for diagnosis, monitoring, and prognosis.

Note : This document serves educational purposes exclusively and does not constitute medical advice or treatment guidelines