Binocular Vision Lecture 8: Convergence & Accommodation | Part 2

Binocular Vision Lecture 8 - Convergence and Accommodation Part 2

• Learning Objectives: Discuss management of convergence and accommodation insufficiency, understand AC/A ratio calculation, and relate AC/A ratio values to binocular vision difficulties.

Convergence Insufficiency

• Definition: Inability to obtain or sustain sufficient convergence for binocular vision at near.

• Symptoms: General difficulties with near vision, tired or sore eyes, intermittent diplopia (double vision), headaches. Symptoms worsen with tiredness or illness.

• Signs: Reduced near point of convergence (NPC), poor response to jump convergence tests, decompensating exophoria (eyes turn outwards at near), and potentially reduced accommodation.

Convergence Insufficiency Management

• Interventions:
  • Office-based vergence/accommodative therapy (with home reinforcement): More effective than home-based methods for children; less clear evidence for adults.
  • Base-in prism reading glasses: Not effective for young adults, but possibly helpful in adults (though not conclusive). Trials show symptom reduction but no improvement in NPC.
  • Exercises: Vision therapy exercises (e.g., target/pencil push-ups), stereograms, lifesaver cards, and computer orthoptics.
  • Pen-to-nose exercises: Patient brings a pen close until diplopia is observed, then moves it away until single vision is restored.
  • Brock string exercises: A string with beads is used to guide the patient's eyes' convergence and divergence.

Accommodation Insufficiency

• Definition: Inability to obtain or maintain sufficient accommodative focus at near, relative to expected age-related accommodation.

• Symptoms: General difficulties with near vision, tired or sore eyes, blurred near vision, headaches. Symptoms worsen with fatigue or illness.

• Signs: Reduced amplitude of accommodation (relative to expected value); reduced accommodative facility, convergence insufficiency often co-occurs, and an accommodative lag > 1.00D measured with dynamic retinoscopy.

Accommodation Insufficiency Management

• Treatment: Reading spectacles are the primary treatment.
• Discouraged/Insufficient Evidence: Accommodation exercises (ramp, jump, Lens Flipper) currently lack strong evidence of effectiveness. Further research is needed in this area.

Accommodative Exercises for Presbyopes

• Ineffectiveness: Current research indicates that accommodative exercises are ineffective in correcting presbyopia.

Ramp Accommodation

• Procedure: Begin with writing at 1/2 meter distance, gradually moving it closer until the patient loses focus, then move it away until focus is restored. Repeat the process.
• Frequency Recommendation: 2 minutes at a time, 5 times a day.

Jump Accommodation

• Procedure: Use two targets, one near and one at distance, and ask the patient to rapidly shift focus between them.
• Frequency Recommendation: 2 minutes at a time, 5 times a day.

Lens Flipper (Lens Rock) Exercises

• Procedure: Patient wears distance correction; target is held 40cm away (small print). The examiner uses positive and negative lenses (+/- 2.00D) to shift the focus.
• Frequency Recommendation: 2 minutes at a time, 5 times a day.

AC/A Ratio

• Definition: The amount of accommodative convergence (AC) induced by one diopter of accommodation (A).

• Normal Range: Typically between 3–5 units of accommodative convergence for each unit of accommodation.

• Low AC/A Ratio: Indicates insufficient convergence when accommodating. Often associated with convergence insufficiency, exophoria, or exotropia.

• High AC/A Ratio: Indicates excessive convergence when accommodating. Often associated with convergence excess, esophoria, or esotropia.

• Relationship to Age: The AC/A ratio remains relatively constant until presbyopia onset, and is thus less clinically useful in presbyopic patients. Calculation and gradient methods can measure the AC/A ratio.

• Methods for Measuring AC/A:

  • Calculation Method: A formula involving the patient's pupillary distance (PD), fixation distance (at near), and phorias (at near and distance).
  • Gradient Method: Measures the phoria with and without corrective lenses to determine the change. Includes modified gradient method using Maddox Wing and appropriate lens power.