Binocular Vision Lecture 8: Convergence & Accommodation

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Questions and Answers

What is the primary formula to calculate the AC/A ratio?

AC / A = PD - ( n ´ ( D' + D))

AC / A = PD + ( n ´ ( D' + D))

AC / A = PD + ( n ´ ( D' - D)) (correct)

AC / A = PD - ( n ´ ( D' - D))

What does a higher AC/A ratio indicate about a patient's phoric condition?

Requires less accommodative effort

Normal near fusion ability

Higher levels of exophoria

Greater convergence response to near stimulus (correct)

When using the basic gradient method, what is the result if the baseline phoria is 8Δ exo and the phoria measured with -1.00D lens is 2Δ exo?

AC/A ratio of 2/1

AC/A ratio of 6/1 (correct)

AC/A ratio of 8/1

AC/A ratio of 4/1

In the modified gradient method, how is the near phoria affected by the addition of a -2.00DS lens?

It is measured again and will be negative for exophoria. Signup and view all the answers

Which method provides a quick and easy measure of the AC/A ratio?

Gradient Method Signup and view all the answers

If a patient has a pupillary distance of 60 mm and experiences 3 dioptre exophoria at distance and 12 dioptre exophoria at near, what is the calculated AC/A ratio?

3.6D Signup and view all the answers

What is the effect of proximal vergence on the calculated AC/A ratio?

It is not included in the calculation. Signup and view all the answers

Why is recording findings of calculated and modified gradient tests only valuable in pre-presbyopes?

Pre-presbyopes still rely on their accommodative abilities. Signup and view all the answers

What is the primary challenge associated with convergence insufficiency?

Inability to obtain or maintain sufficient convergence for binocular vision at near. Signup and view all the answers

Which symptom is least commonly associated with accommodation insufficiency?

General difficulties with distant vision. Signup and view all the answers

What is the significance of the AC/A ratio in relation to binocular vision?

It quantifies the relationship between accommodative convergence and accommodation. Signup and view all the answers

Which management option for convergence insufficiency is not effective for young adults?

Base-in prism reading glasses. Signup and view all the answers

How does a high AC/A ratio affect a patient's convergence ability?

They will over-converge when accommodating. Signup and view all the answers

Which exercise is designed to improve accommodation insufficiency?

Jump accommodation exercises. Signup and view all the answers

What is an expected clinical sign of convergence insufficiency?

Reduced near point of convergence (NPC). Signup and view all the answers

What should be observed in patients with accommodation insufficiency during dynamic retinoscopy?

Accommodative lag greater than 1.00D. Signup and view all the answers

What is the expected AC/A ratio for a patient with normal convergence and accommodation?

3 to 5 units of accommodative convergence per dioptre of accommodation. Signup and view all the answers

What is NOT a characteristic symptom of convergence insufficiency?

Difficulty maintaining clear distance vision. Signup and view all the answers

Which of the following exercises does not have sufficient evidence supporting its effectiveness for accommodation insufficiency?

Ramp accommodation exercises. Signup and view all the answers

What is an essential requirement for performing lens flipper exercises?

The writing target should be at least 40 cm away. Signup and view all the answers

What typically characterizes the management approach for accommodation insufficiency?

Two distinct methodologies without clear evidence of effectiveness. Signup and view all the answers

What is the correct formula for calculating the AC/A ratio?

AC / A = PD + ( n × ( D' - D)) Signup and view all the answers

Study Notes

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.

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Description

Explore the complexities of binocular vision, particularly focusing on convergence and accommodation insufficiency. This lecture covers the symptoms, management strategies, and AC/A ratio calculations essential for understanding binocular vision difficulties. Ideal for those interested in vision science and therapy methods.

Binocular Vision Lecture 8: Convergence & Accommodation | Part 2

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