Clinical Management of Primary Divergence Insufficiency_Bhattacharya S

Background

Divergence insufficiency (DI) is a non-strabismic binocular vision disorder characterized by a greater degree of esophoria or intermittent esotropia at distance and single binocular vision at near (Thomas, 2000). Unlike divergence excess, where the deviation is larger at distance but with an exophoric component (Kushner & Morton, 1998). Divergence insufficiency presents with an inward eye misalignment that is more prominent when focusing on far targets. This condition often causes patients to experience intermittent diplopia, blurry distance vision, eyestrain, and difficulty with distance-related visual tasks such as driving, watching movies, or attending lectures (Jacobson, 2000).

Physiologically, divergence refers to the outward movement of both eyes to maintain single binocular vision when focusing from near to far objects (Chen et al., 2010). In divergence insufficiency, this mechanism is underactive or delayed, resulting in over-convergence for distance targets (Prangen & Koch, 1937). Primary divergence insufficiency is generally a benign condition that is commonly associated with decompensation of a longstanding esodeviation, loss of sensory or motor fusion (Kirkeby, 2014). Many affected patients experience spontaneous resolution of double vision within resumption of binocular fixation, but it will usually reappear as one proceeds to fatigue divergence by repeated tests of ability to overcome prism base in (Prangen & Koch, 1937). The clinical neurologic evaluation is a powerful tool that distinguishes those with a primary divergence insufficiency from those harbouring an underlying neurologic or secondary divergence insufficiency (Jacobson, 2000). It is more commonly observed in adults over the age of 30 but can also occur in younger populations with females having higher preponderance as for the incidence of patients with divergence insufficiency was found to be 6% (Kirkeby, 2014). Clinical diagnosis involves careful measurement of ocular alignment at both distance and near. A hallmark sign of DI is a higher esophoria at distance, often revealed during cover tests and confirmed using tools like the Maddox rod. Fusional vergence testing typically shows reduced divergence amplitudes at distance (Godts & Mathysen, 2013). Divergence insufficiency is not uncommon in patients with high myopia. Patients with esotropia secondary to high myopia commonly present with progressive horizontal diplopia at distance (Kohmoto et al., 2011).

Management of Divergence insufficiency usually begins with compensatory strategies like base-out prism glasses; however, vision therapy has proven to be an effective long-term treatment (Iliescu et al., 2017). Therapy focuses on improving divergence amplitudes and developing voluntary control of eye alignment during distance fixation (Berscheid, 2005). Techniques such as stereograms, vectograms can be employed to strengthen distance fusional divergence.

Case Report

A 25-year-old female presented with complaints of intermittent diplopia and visual discomfort, especially during distance viewing activities such as driving and watching television. Visual acuity was 6/6 in each eye. The patient had no notable ocular or systemic history. He was referred for a comprehensive binocular vision assessment due to persistent symptoms.

Diagnostic Findings

1. Visual Acuity: Visual acuity was measured using a Snellen chart at both distance and near, revealing 6/6 and N6 vision in each eye respectively.

2. Cover Test: Near and distance cover tests were performed 6 prism diopter esophoria at distance, 2 prism dioptre esophoria at near was found(BO).

3. Maddox Rod Test: Confirmed greater esodeviation at distance than near.

4. Stereopsis: Stereopsis was assessed using the Randot Stereo test, revealing normal at near (40 seconds of arc).

5. Extraocular Movements (EOM): EOM were assessed to rule out any muscle weakness or restriction. The patient demonstrated full extraocular movements in both eyes in all cardinal gazes.

6. Positive Fusional Vergence (PFV) at distance: PFV was measured using a prism bar, revealing a break point of 5 PD.

7. Negative Fusional Vergence (NFV) at distance: NFV was measured using a prism bar, revealing a break point of at 2 PD.

8.     Amplitude of Accommodation (AOA): AOA was measured using the push-up method, revealing an amplitude of 12 dioptres, indicating no accommodative dysfunction.

9.     Monocular Estimation Method (MEM): MEM was performed to assess the patient's ability to estimate distance accurately, revealing normal distance estimation.

10.  Vergence Facility: Vergence facility was assessed using flipper lenses, revealing a facility of 6 cycles per minute.

Diagnosis

The patient was diagnosed with primary divergence insufficiency, characterized by greater esophoria at distance than near, reduced distance fusional divergence, and associated symptoms of intermittent diplopia, especially during distance viewing tasks like driving and watching television.

Prognosis

With consistent adherence to a structured 12-week vision therapy program, the prognosis for this patient is highly favourable. As the amount of deviation is less than typically seen in most divergence insufficiency cases, significant improvements in fusional vergence, reduction in symptom, and binocular stability are more readily achievable, supporting long-term visual comfort and functionality with appropriate follow-up and maintenance exercises.

Vision Therapy Plan:

The treatment plan involved vision therapy session twice a week for 12 weeks and divided into 3 phases (2 sessions/week):

Phase 1: We need to improve fusional Awareness and Base Divergence Control (Weeks 1–4)

In-Office Therapy (2 sessions/week):

• Brock String: 15 min.

Using a Brock string, the patient will practice divergence by focusing on beads along the string at various distances.

• Tranaglyphs or Vectograms (Base-In): 15 min.

We have to start with peripheral targets (e.g., Tranaglyph 515, Quoit vectogram).

• Bug on a String: 15 min.

We have to encourage the patient to promote their spatial localization.

Home Therapy:

• HTS Vergence & Accommodation Software: 15 min daily.

We have to encourage the patient to do this exercise daily to reinforce clinical therapy efficacy.

• Brock String Practice:10 min daily.

Phase 2: We have to start enhancing the divergence amplitudes (Weeks 5–8)

In-Office Therapy (2 sessions/week):

• Bug on a String: 15 min.

We have to encourage the patient to look at the bug placed farther down the string. The string will appear X shape when the fusion is accurate.

• Aperture Rule Cards: 15 min.

We have to introduce jump vergence demand to train the patient to rapidly shift vergence from one level to another.

• Binocular Accommodative Therapy: 15min.

 We have to integrate vergence with lens shifts by challenging the accommodative system using plus and minus lenses.

• Eccentric Circles: 15 min.

At 40 cm for convergence and divergence. The patient must converge/diverge the eyes to align the concentric circles properly.

Home Therapy:

• HTS Vergence & Accommodation Software: 10min.

 We have to encourage the patient to do this exercise daily to reinforce clinical therapy efficacy.

• Eccentric Circles (Base-In): 10 minutes daily.

Phase 3: We will focus on distance generalization and stabilization (Weeks 9–12)

In-Office Therapy (2 sessions/week):

• Vectograms/Tranaglyphs at 1 m: 15 min.

With step-jump vergence emphasis. Here, we have to encourage the patient to quickly respond to changes in depth, just like real-world visual demands.

• Aperture Rule: 15min.

We have to introduce jump vergence demand to train the patient to rapidly shift vergence from one level to another (1m)

• Computer Orthoptics Random Dot Program: 15min.

We have to use a step-jump base-in at 1 m.

Home Therapy:

• Large Eccentric Circles (Distance): 10 minutes daily.

The patient must converge/diverge the eyes to align the concentric circles properly.

• Maintenance home therapy including distance fixation with prism flippers: 10 minutes daily.

Discussion:

Divergence insufficiency can impair quality of life, especially during sustained distance tasks, and is often mistaken for refractive error. Despite a milder-than-average deviation, the patient experienced notable visual strain during distance tasks.  As in this case structured vision therapy led to marked symptomatic relief and functional improvement. This case highlights the effectiveness of early diagnosis and vergence-focused, non-surgical rehabilitation in mild presentations.

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