Assessment of binocular vision in children with and without neurodevelopmental disorder

Dear Editor,

Although ocular manifestations in neurodevelopmental anomalies have been explored, binocular vision disorders in affected children remain underexplored. This letter seeks to highlight the relevance of incorporating structured binocular vision assessment into pediatric eye care for this population.

This prospective study was approved by the institutional ethical committee and followed the Declaration of Helsinki. Participants were included after obtaining informed consent from the guardians of the children. A control group (CG) of 106 healthy children was recruited from normal schools, and 107 children in the neurodevelopmental disorder group (NDDG) from special schools. The excluded were noncooperative children, those who underwent ocular surgery and previous visual training, and those with systemic diseases at the time of examination. After obtaining a detailed history, all the study participants underwent a comprehensive eye examination. The accommodation, vergence, and stereopsis were evaluated using appropriate procedures.

The NDDG comprised subjects with intellectual disability (42.9%), specific learning disability (36.4%), Down syndrome (10.28%), attention-deficit/hyperactivity disorder (4.67%), autism spectrum disorder (3.73%), and cerebral palsy (1.87%). A statistically significant difference in near point of convergence (NPC), negative fusional vergence (NFV), positive fusional vergence (PFV), and accommodative convergence/accommodation ratio was observed between the NDDG and CG (P value <0.001). A higher number of patients with exophoria and esophoria was found in NDDG than in the controls (P value <0.001). A statistically significant difference (P < 0.05) was observed in accommodative facility and response between the groups [Table 1]. A higher prevalence of vergence dysfunction and lower stereopsis was reported in the NDDG (P < 0.001) [Table 2].

Table 1.

Summary of the results of accommodative and vergence examination among CG and NDDG

Variables				CG		NDDG		χ 2		P
NPC		<8		47 (44.3%)		56 (52.8%)		26.57		<0.001
		8-10		48 (45.3%)		17 (16.0%)
		>10		11 (10.4%)		33 (31.1%)
PHORIA		Exophoria		5 (13.2%)		33 (86.8%)		30.24		<0.001
		Esophoria		0		4 (100%)
		Orthophoria		101 (59.1%)		70 (40.9%)
NFV BREAK		<4		0		9 (8.4%)		9.36		<0.01
		4-26		93 (87.7%)		87 (81.3%)
		>26		13 (12.3%)		11 (10.3%)
NFV RECOVERY		<7		18 (17%)		35 (32.7%)		7.18		<0.05
		7-15		50 (47.2%)		43 (40.2%)
		>15		38 (35.8%)		29 (27.1)
PFV BREAK		<16		36 (34%)		70 (65.4%)		21.68		<0.001
		16-36		67 (63.2%)		34 (31.8%)
		>36		3 (2.8%)		3 (2.8%)
PFV RECOVERY		<11		36 (34%)		62 (58.5%)		12.82		<0.001
		11-31		70 (66%)		44 (41.5%)
		>31		0		0
AC/A RATIO		<3		4 (3.8%)		21 (19.8%)		17.06		<0.001
		3-5		2 (1.9%)		7 (6.6%)
		>5		100 (94.3%)		78 (73.6%)
MEM		<.25		2 (1.9%)		10 (9.3%)		8.75		<0.05
		.25-.75		97 (91.5%)		83 (77.6%)
		>0.75		7 (6.6%)		14 (13.1%)
AF		<6		21 (19.8%)		38 (35.8%)		6.8		<0.01
		6-19		85 (80.2%)		68 (64.2%)
NRA		≤ 1.50		0		4 (3.8%)		4.9		0.086
		1.75-2.50		23 (21.7%)		17 (16.2%)
		>2.50		83 (78.3%)		84 (80%)
PRA		≤ 1.25		0		5 (4.8%)		8.5		0.014
		1.50-3.50		22 (20.8%)		32 (30.5%)
		>3.50		84 (79.2%)		68 (64.8%)

CG: Control group, NDDG: Neurodevelopmental disorder group, NPC: near point of convergence, NFV: negative fusional vergence, PFV: positive fusional vergence, AC/A ratio: Accommodative accommodation ratio, MEM: monocular estimation method, AF: Accommodative facility, NRA: Negative relative accommodation, PRA: Positive relative accommodation

Table 2.

Distribution of Vergence, Accommodative, and Stereopsis status among CG and NDDG

Binocular Status		CG (106) n (f)		NDDG (107) n (f)		P
Vergence status
Normal		102(96.2%)		87(81.3%)		<0.001
CI		4(3.8%)		17(15.9%)		<0.01
CE		(0)		2(1.9%)		>0.05
DE		(0)		1(0.9%)		>0.05
Accommodative Status
Normal		105(99.1%)		105(88.1%)		0.566
AI		1(0.9%)		2(1.9%)
Stereopsis
Normal		103(97.2%)		52(48.6%)		<0.001
low		3(2.8%)		55(51.4%)

CG: Control group, NDDG: Neurodevelopmental disorder group, CI: Convergence insufficiency, CE: Convergence excess, DE: Divergence excess, AI: Accommodative insufficiency

Among the vergence dysfunctions, convergence insufficiency was common in NDDG compared to the controls and this was consistent with the study conducted by Granet et al.[1] and contrary to the study by Bilbao et al.[2] In our study, NPC values were outside the normal limit in 31.1% in NDDG; this was similar to the study conducted by Bilbao et al.[2] and contrary to results of Ababneh et al.[3] Our study obtained a statistically significant difference in fusional vergences contrary to the study by Coulter et al.[4] and Bilbao et al.[2] Accommodative response and facility were significantly different; this was comparable to the study conducted by Anketell et al.[5] Also, NDDG displayed poorer stereopsis compared with CG and was line with the result of Bilbao et al.[2] and Coulter et al.[4]

The major limitation of this study was that the majority of the binocular vision parameters were measured subjectively, which was challenging in children with neurological disorders, and these assessments may not be concise. Since the incidence of binocular vision disorders was higher in NDDG, binocular status assessment should be incorporated into the routine eye checkup for this special population, which improves their quality of life.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.