Case 3 A 12-year-old female student presented with complaints of asthenopia, occasional inward deviation of her left eye, and headache, which had gradually increased over the past four years. Her headache worsened, particularly when she had to take notes from the board at school. Pain relief medication was used, but her symptoms did not improve. She had not undergone an eye examination in the past four years. Her mother denied any history of trauma, systemic illness, or medication use. She had normal sleep patterns as well. Unaided visual acuity was 6/6 (N6 at 40 cm) in each eye. Both dry and cycloplegic refractions were performed. Dry refraction revealed plano OD, OS, while cycloplegic refraction showed +0.25 OD, +0.50 OS. She did not require any glasses for refractive error correction. A binocular vision evaluation was conducted (Table 5). The cover test revealed a comitant, high-frequency left intermittent esotropia of 2∆ at near and a constant left esotropia of 12∆ at distance. The Worth four-dot test showed left eye suppression at both distance and near. She had poor negative fusional vergence for both near and distance, measured as 2/x (break/recovery). Fusion was achieved only when using peripheral fusional target slides on the synoptophore. Stereoacuity was absent. She was diagnosed with DI with normal correspondence. The angle of deviation was small, so strabismus surgery was not recommended. The options of vision therapy and prism glasses were discussed with the mother (Table 6). The initial goal was to eliminate suppression, followed by establishing binocularity, maintaining fusion, and strengthening the negative fusional vergence. Once suppression was eliminated, relieving prism glasses (2∆ BO OD, OS) were used to maintain fusion. Prism glasses (Plano with 2∆ BO OD, OS) were worn to maintain fusion. Positive fusional vergence at near was evaluated prior to prescribing prism glasses and was found to be sufficient, allowing the patient to comfortably tolerate the prism during near work. The therapy was continued with the glasses until negative fusional vergence was strong enough to control the deviation. An evaluation was performed after 10 weeks (Table 5). The patient was asymptomatic, and negative fusional vergence was normal. We advised continuing home-based therapy and bi-annual follow-up. Discussion This case series highlights that vision therapy, in combination with prism lenses, is an effective treatment option for DI. All three patients showed improvement in visual symptoms, negative fusional vergence, and the frequency of deviation. The etiology of the DI in these patients was unclear. DI must be differentiated from divergence paralysis and sixth nerve paresis.16 The comitant nature, occasional double vision (more pronounced at distance) that increased over time and disappeared after rest, and the gradual onset help to differentiate DI from sixth nerve paresis and divergence paralysis.16 To determine the best management plan, a thorough evaluation is necessary, which includes a detailed case history, sensorimotor examination, and neurological imaging.17 An MRI was performed in each case above as a precaution. A sensorimotor exam should include checking the patient’s visual acuity, determining the angle of deviation, and evaluating the level of stereopsis and amplitudes of negative fusional vergence. The management of DI lacks a standardized approach. Typically, prism or surgery are the initial treatment strategies.15 A recent prospective study showed that surgery provides superior outcomes compared to prism glasses.15 There is limited literature available on the effectiveness of vision therapy for DI,16 but several studies suggest Optometry & Visual Performance 257 Volume 13 | Issue 4 | December 2025 Test Before Therapy Final Visit (After 5 Months) BCVA RE: 6/6 (N6 @ 40cm) with plano LE: 6/6 (N6 @ 40cm) with plano RE: 6/6 (N6 @ 40cm) with plano LE: 6/6 (N6 @ 40cm) with plano Cover test (with correction) Near: 2∆ intermittent left esotropia with poor control Distance: 12∆ intermittent left esotropia with poor control Near: orthophoria Distance: 8∆ esophoria Gradient AC/A 3:1 3:1 NFV (break/recovery) Near: 4/2 Distance: 2/x Near: 20/16 Distance: 14/10 Worth four-dot test Near: left suppression Distance: left suppression Near: binocular single vision Distance: binocular single vision Stereopsis (Titmus fly) Absent 50 sec of arc Correspondence (with synoptophore) Normal Normal Table 5. Orthoptic Findings Before and After VT: Case 3
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