Prevalence of Non Strabismic Binocular Vision Dysfunction among Engineering Students in Nepal

Non-Strabismic Binocular Vision Dysfunctions (NSBVD) are visual disorders that affect the subject’s binocular vision and visual performance, especially when performing tasks requiring near vision. They occur when the accommodative and/or vergence response of the visual system is defective. As a result, the visual system may suffer a loss of efficiency, hindering near vision activities [1]. The most frequently encountered disorders of the binocular vision system include convergence insufficiency/excess and divergence insufficiency/excess. Oculomotor dysfunction shows inaccurate and inefficient pursuits and saccades. Focusing problems frequently include accommodative insufficiency, excess/spasm, instability, infacility, and ill-sustained accommodation. These dysfunctions are commonly of associated symptoms, including blurred vision, difficulty in focusing at different distances, headache and ocular pain, and difficulty with focusing particularly when reading and writing [1-3]. However, the symptoms that the subjects perceives may differ depending on the type of causative disorder [4].

NSBVD are common in the pre-presbyopic population which results in less productivity in academic and other near vision-oriented tasks [2-8]. Undiagnosed binocular vision and oculomotor dysfunction may present with discomfort which can have a negative impact on academic performance [2-8]. The prevalence of accommodative and binocular vision disorder is 8.5 times greater than the prevalence of ocular disease in children between 6 to 18 years [9]. It is estimated that 7-10% of the general population has some type of problem with accommodation and binocular functioning [10]. Several authors have shown that these disorders are commonly found in clinical practice, although there is some disparity in th prevalence reported in the various published studies [5,9-15]. Garcia et al. [12] in 2016 undertook a cross-sectional study on randomized sample of 175 university students aged 18 to 35 years. The overall prevalence of accommodation and binocular dysfunction was 13.5% and refractive dysfunction was 45.14%. Dahal et al. [13] in a study on optometry students in Bangalore India in 2019 found the prevalence of non-strabismic accommodative dysfunction to be 55.00%, vergence dysfunction to be 73.00% and oculomotor dysfunction to be 15.00%. Engineering is one of the disciples of science which needs tedious near works, long run computer tasks and accurate focus and fixation. Excessive near work results in NSBVD which directly impact on academic performance of students [2-8]. This study was conducted to assess the prevalence of NSBVD among engineering students in Nepal.

A cross sectional study was carried out among engineering students of age 18 to 30 year in different engineering colleges in Kathmandu valley (Kathmandu, Lalitpur and Bhaktapur districts), within a period of 6 months. The study began after taking permission from the college authorities & fixing the date for the evaluation of NSBVD of the students. The criteria for selection were the absence of significant uncorrected refractive error, healthy eyes, and no strabismus or amblyopia. Clinical setup was divided into two stations. The first station was for taking detail history on visual symptoms, measurement of visual acuity at distance and near, refraction (objective & subjective without dilation), sensory and motor evaluation. The tests included the measurement of stereopsis using stereo fly, worth-4-dot test, cover test at distance and near, prism bar cover test, measurement of AC/A ratio using gradient method and maples ocular motility test. Second station included the assessment of accommodation and vergence. The different tests for accommodation were measurement of Near Point of Accommodation (NPA) monocularly and binocularly using word target of using Royal Air Force (RAF) ruler each repeated 5 times, negative and positive relative accommodation (NRA and PRA), Accommodative Facility (AF) monocularly and binocularly and Monocular Estimation Method retinoscopy (MEM). The different tests for vergence were measurement of Near Point of Convergence (NPC) by vertical streak target of RAF ruler repeated 5 times, base in fusional vergence (NFV) and base out vergence (PFV) and vergence facility.

The results obtained from Amplitude of Accommodation, NPC, gradient AC/A, MAF and BAF, MEM retinoscopy, and vergence facility were compared with tables of established expected values by Scheimann & Wick [16] (Table 1). The results from distance and near lateral phoria, NFV, PFV, NRA, and PRA were compared with expected values from the tables of expected values by the Optometric Extension Program (Table 2) [17]. The results from the Maples Oculomotor Test were compared with minimal acceptable scores for saccades and pursuits by age and sex (Tables 3 & 4) [18]. Written consent was taken from each subject before conducting this study. The study protocol adhered to the provision of the Declaration of Helsinki for research involving human subjects. All data were entered into a Microsoft Excel database (Microsoft, version 2010) and analyses were done.

Mechanisms for production of aqueous humor are not fully understood, but it is posited that the Non-Pigmented Ciliary Epithelium (NPCE) anterior to the choroid, is necessarily involved [11]. Recollecting the “Water Drinking Provocative Test,” It seems reasonable to suggest that osmotic factors starting in the early intestinal fluid viscosity should play a role. The bicarbonate ionic mechanisms posited at the NPE might NOT be more primary than osmosis.

Dynamic anatomy and neurology influences

Regulation of aqueous humor drainage is better understood as anatomy, but not well established as far as a physiological model including fluid dynamic rate of flow and neurology [12-16]. Pressure differential at the two chambers anterior to the vitreous might be regulated by pupil neurology and mechanics as the iris sphincter appositionally opens and closes at the margin of the anterior lens. Electron microscopy imaging at the Inner Wall of Schlemm’s Canal (IWSC) is informative [17] but the factors controlling rate of vacuole formation and vesicular bubble pore size for draining internal eye fluid, remain unknown.

Biophysics, histology, inflammation

he flexible and contractile Juxta-Canalicular Tissue Trabecular Meshwork (JCT-TM) is composed in part of collagen, but white blood lymphatic corpuscles emerge and depart with unknown frequency. To maintain the JCT-TM adequately fenestrated physically, is most necessary but biological metabolism and biophysical stressors are barely understood [18]. By simplistic counting of cells it is hard to know whether they serve inflammatory process and gathered in excessive numbers, or whether their main function is phagocyte engulfing of bacteria fragments and debris.

Success and failure

Recent year post-millennium effort to understand glaucoma physiology [19-21] published 2013-2017, has been monumental. Design and results of long-term clinical trials between 1992 and 2005 were not adequately addressing physiological antecedents of eye pressure regulation. Today, it appears necessary that innovation for measurement of eye pressure be directed from a solid understanding of ocular biophysics combined with neural, metabolic and vascular factors. Corneal thickness does not completely represent the mechanics of the cornea and therefore a reasonably good estimation of corneal elastic resistance could be a valuable addition to any new advanced instrumentation for ocular tonometry.

New understanding

When prostaglandins [22,23] were introduced in year 1994, the author observed, that prior standard clinical protocol of betablocker eye drop twice daily was suddenly overturned [24]. Today, a well-described study from mainland China criticizes prostaglandin analog eye drops [25] and we are faced with a conundrum. We need to temporarily favor prior drugs until diagnostic technology reveals better and safe pharmaceutical targets. The genius and dedication of Hans Goldmann [26] might serve as inspiration.

Table 1:Expected findings: Binocular vision testing (Scheimann & Wick) [16]

Table 2:extension program expected findings [17].

Table 3:Maples pursuit test minimal acceptable score by age and sex [18].

Table 4:Maples saccadic test minimal acceptable score by age and sex [18].

In the current study, 210 students were evaluated of age group 18-30 years (mean age 24). No participant was excluded: 147 (70%) were male and 63 (30%) were female. Out of 210 students, 150 students (71.41%) presented with non-strabismic binocular vision dysfunctions, 60students (28.57%) were classified as normal. Of the 150 students with NSBVD, 45 students (21.42%) presented with accommodative dysfunctions, 60 students (28.57%) presented with vergence dysfunctions, 24 students (11.42%) had combined accommodative and vergence dysfunctions and 21 students (10.00%) presented with oculomotor dysfunction. In terms of accommodative dysfunctions, there was a higher incidence of accommodative insufficiency (12.85%) than accommodative infacility (2.85%) and accommodative excess (15.71%). For vergence dysfunctions, the convergence insufficiency was the most prevalent (11.42%) compared to the convergence excess (5.71%), basic exophoria (7.14%) and fusional vergence dysfunction (4.28%). Of 24 students with combined accommodative dysfunction with vergence dysfunction, 12 (5.71%) had combined convergence insufficiency with accommodative insufficiency, 6 (2.85%) had convergence insufficiency with accommodative insufficiency and 6 (2.85%) had convergence excess with accommodative insufficiency. 21 students (10%) had oculomotor dysfunction. 75 students (35.71%) reported symptoms such as headache, blur after reading, and asthenopia while 135 students (64.28%) did not report any symptoms. Table 5 shows the prevalence of NSBVD among engineering students.

Table 5:Prevalence of non-strabismic binocular vision dysfunctions. Source: AD=Accommodative Dysfunctions, BD=Binocular Dysfunctions.

Non strabismic binocular vision dysfunctions is the growing problem, it is very important to know about the population at highest risk and its prevention & management as early as possible. Timely diagnosis of the conditions can improve the prognosis of binocular dysfunction. This condition is usually associated with prolonged near work [2,3,5,19]. In the current study, the overall prevalence of NSBVD was 71.41%. The major problem was accommodative insufficiency followed by convergence insufficiency and oculomotor dysfunction. In our study, the prevalence of NSBVD was distinguished from other studies. Numerous study results agreed that accommodative dysfunctions were more prevalent than vergence dysfunctions [2,19,20] whereas in the present study, the prevalence of vergence dysfunctions was higher. Hokoda et al. [20] in studied 119 patients; 42.9% of the patients had jobs with near workloads, and 39.5% of the patients were students with near workloads. In this particular study the prevalence of accommodative dysfunction was significantly higher than that of vergence dysfunction particularly accommodative insufficiency was the most prevalent. In addition, in Montes-Mico’s [10] study with a significant number of participants, accommodative dysfunctions were more prevalent than vergence dysfunctions. However, in our study, vergence dysfunctions were more prevalent than accommodative dysfunction. Dahal et al. [13] in a study on optometry students in India found the prevalence of vergence dysfunction significantly higher than accommodative dysfunctions which supports our study.

The present study revealed a high prevalence of NSBVD among engineering students and 35.71% of the students were symptomatic. These findings suggest that in engineering students, it is important to conduct a thorough eye and binocular vision examination to detect NSBVD. Furthermore, these dysfunctions can be successfully managed through the art of lens prescribing and optometric vision therapy [21-26]. Therefore, timely diagnosis and management will positively impact their future and increase the productivity of life.

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Manish D, Kaiti R, Bishal H (2019) Evaluation and Management of refractive amblyopia with associated non strabismic binocular vision dysfunctions through vision therapy: A case report from Nepal. EC Ophthalmology Case Report 10: 1-8.

25  .Raju K, Manish D, Bishal H (2020) Management of accommodative insufficiency with optometric vision therapy: A case report. J Ophthalmol 5(1):1-3.