The prevalence of non-strabismic binocular vision anomalies is on the rise over the last decade. The prevalence reports from various parts of the globe quote a high prevalence ranging between 28.5-31.5% among school children (1,2). It is also shown in a recent study that clinically significant convergence insufficiency can impair stereo-acuity in children necessitating the diagnosis and management of convergence insufficiency (3). Here are some pearls to ensure accurate diagnosis and provide appropriate management to patients afflicted with binocular vision anomalies. This article specifically focuses on non-strabismic binocular vision anomalies as they are often missed out due to their latent nature, unlike strabismic anomalies.
The efficiency of the visual system is beyond 20/20
Many eye care practitioners unfortunately still assume that 20/20 visual acuity ensures an optimally functioning visual system. The efficiency of the visual system is not just dependent on the integrity of the visual apparatus, and monocular visual acuities, but also on a well-functioning and integrated binocular vision (BV). So, when a patient complains of asthenopic symptoms unexplained by a regular eye examination, a comprehensive binocular vision assessment is warranted even in the absence of significant refractive errors (2). Binocular vision assessment is also indicated in Anisometropia, Keratoconus (4,5), amblyopia (6), and Myopia (7,8).
Binocular vision anomalies are common among children with special needs
Children with special needs are often considered a challenge during an eye examination due to the reduced accuracy of subjective responses and the need for skilled professionals. This makes specialized testing such as a binocular vision assessment more complicated. Nonetheless, it is imperative to understand that children with special needs are at an increased risk of binocular vision dysfunctions. Children with Down syndrome are shown to have reduced accommodation capabilities for their age requiring the need to provide appropriate refractive correction (9, 10). Children with Autism and learning disabilities also require careful evaluation of binocular vision so that remediation of these dysfunctions can potentially impact the vision-related quality of life of this special population (11, 12).
A comprehensive evaluation of binocular vision
A comprehensive evaluation of binocular vision should include testing for accommodation, and vergence parameters in addition to tracking and reading eye movement parameters wherever applicable. The comprehensive test battery for BV assessment should include testing for near point of convergence, near point of accommodation, relative accommodation, accommodation response and facility, vergence amplitudes and facility, distance and near phoria, and the Accommodation convergence to accommodation (AC/A) ratio (13). Appropriate refractive corrective and binocular balancing are nonetheless the foundational aspects before venturing into a BV testing.
Binocular vision assessment is important before refractive surgery
It is important to evaluate binocular vision prior to refractive surgery, as various studies have emphasized the importance of a normal binocular vision reducing the risks of post-operative complications due to decompensated vergence and accommodation anomalies. Any pre-operative anisometropia, vertical deviations, and asthenopic symptoms associated with binocular vision dysfunctions require careful evaluation prior to refractive surgery (4,5,14).
Binocular vision in Digital device use
With increased digital device use across the globe among all age groups, the prevalence of digital eye strain has skyrocketed. Subjects who have deficient accommodation and vergence parameters are at risk of developing symptoms with digital device use. It is therefore important to evaluate binocular vision apart from assessing ocular surface and Ergonomic considerations (15,16).
Binocular vision assessment after a traumatic brain injury
The association between binocular vision dysfunctions following a traumatic brain injury such as concussion, and closed head injury is reportedly high (17,18). Apart from evaluation of eye health following a brain injury, it is important to evaluate for accommodation dysfunctions, decompensated heterophoria, vertical muscle imbalance and convergence insufficiency following a traumatic brain injury. Diffuse axonal injury associated with the coupe-countercoup injury as seen in whiplash and concussion related injuries can lead to a wide verity of binocular vision dysfunctions, even if the structural brain imaging appears normal.
Receded near point of convergence is not necessarily convergence insufficiency
Receded near point of convergence has always been considered as the hallmark to diagnose convergence insufficiency. But more and more literature emphasize the fact the receded near point of convergence could also be seen in accommodative dysfunctions as in accommodation insufficiency (19, 20). It is important to consider a group of findings such as receded NPC, large near exophoria, and reduced positive fusional vergence amplitudes (13). As the management plan varies between convergence and accommodation insufficiency, it is important to get the right diagnosis.
Children do have accommodative insufficiency
In general, it is believed that children possess normal or excessive ocular accommodation. Nonetheless, in the presence of asthenopic symptoms, visual fatigue, and difficulty with near tasks, clinicians should evaluate the near point of accommodation even among children. A large proportion of children with convergence insufficiency are shown to have associated accommodation insufficiency (19, 20). It is also important to use age and ethnicity appropriate cut-off values to diagnose accommodation anomalies (21).
Minimum test battery to screen for BV anomalies
In community-based school eye health programs, the minimum test battery to screen for binocular vision anomalies can be used as the first step to evaluate children who present with asthenopic symptoms in the absence of significant refractive error. The minimum test battery includes testing NPC with red-green filter, monocular accommodative facility with +2.00 DS/-2.00 DS accommodation flippers, and assessment of near phoria (22). Based on the current prevalence estimates, convergence insufficiency, and accommodative infacility are reported to be most prevalent among school children (2). Hence it is important to screen for these anomalies. Based on the outcome of these testing, further BV assessment and vision therapy can be planned.
The scientific validity of vision therapy
Vision therapy has always been a subject of debate as clinicians have relied upon historical tools and techniques such as the Pencil push-up and Synoptophore based training for binocular vision anomalies. With the concrete and convincing evidence that came out of the Convergence insufficiency treatment trial (CITT) regarding the efficacy of vision therapy using a structured protocol, the scientific validity of vision therapy has been well established (23). It is important that an eye care practitioner adapt to evidence based practice patterns and also be open to exploring engaging and innovative tools that can improve patients’ compliance to a greater extent. Cost-effective indigenous tools (6) have made both testing and management for binocular vision anomalies an easy-breather for clinicians.
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