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Abstract
Objectives To determine detailed oculo-visual characteristics of children with intellectual disability studying in special schools and explore the burden of visual impairment.
Design of the study Detailed ophthalmic examination was carried out in all pupils studying at the seven special needs schools of Kathmandu valley, Nepal. Ophthalmic examination included case history, presenting distance visual acuity, cycloplegic refraction, binocular vision examination, contrast sensitivity and anterior and posterior segment evaluation.
Main outcome measures Ocular and visual status of children.
Results Refractive errors (40%) and strabismus (17%) were the commonest visual disorders in our study children. Ninety-five per cent of the children who had clinically significant refractive errors presented without any correction. Visual impairment was present in 25% of the children. Severe visual impairment or worse was present in 3% of the children. Other common ocular findings were conjunctivitis, blepharitis, chalazion and ectropion.
Conclusions High prevalence of preventable visual impairment in this population requires immediate attention. It is hoped that the formulation of proper vision care guidelines at a national level may help in early detection and management of visual disorders in this special population and enhance their quality of life.
- Ophthalmology
- School Health
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What is already known on this topic
Ocular and visual disorders are common in children with intellectual disabilities.
Most of the visual disorders are treatable with good visual outcome.
There has been a great progress in the field of vision care for children with intellectual disability (ID) in developed countries.
What this study adds
The prevalence of avoidable visual impairment in children with ID in Nepal is significantly higher than typically developing peers.
This is the first study done in children with ID from a developing country that reports detailed visual characteristics including visual impairment and blindness.
Introduction
Ocular and visual disorders such as refractive errors, strabismus, nystagmus, cataract, reduced visual acuity (VA) and poor accommodation are found to be more common in children with intellectual disabilities (IDs) than in typically developing (TD) children.1–9 Studies have shown that up to 86% of children with IDs have oculo-visual disorders.5–8 There has been an increased interest in determining the prevalence of oculo-visual disorders in children with ID for the past decade. Clinicians and researchers have emphasised the importance of early detection and treatment of such disorders as early as possible in life. A considerable amount of literature has been published on visual disorders in children with ID from developed countries, and this has led to a significant progress towards creating awareness among parents and professionals. However, there is still a poor understanding of the prevalence and awareness of such disorders among developing countries.
The purpose of this study was to report detailed oculo-visual disorders present in children with ID studying at special schools of Kathmandu valley, Nepal. Our study also aimed at determining the magnitude of visual impairment (VI) and blindness among children with ID.
Methods
Children were recruited from seven special education schools of Kathmandu valley. Medical records of children were assessed to determine their eligibility criteria.
Ophthalmic examination
VA was assessed using one of three tests depending upon the cooperation and severity of the disability of the child: Keeler Acuity Test (a preferential looking test using grating stimuli) was used for non-verbal and uncooperative children, whereas either Kay Pictures or a Snellen acuity chart was used for those with higher cognitive skills and good cooperation. Monocular as well as binocular VA measurements were attempted in all children. The Keeler Acuity Test was used at a distance of 50 cm, the Kay Picture test at 3 m and the crowded Snellen chart at 6 m. The manufacturer's instructions were followed for each of the tests.
Presence or absence of manifest strabismus was observed using cover test, and the amount of deviation, if present, was determined using the prism cover test, Hirschberg test or Krimsky test, whichever was possible. The size of the deviation, if any, was classified as small (≤15°), moderate (>15 to <30) and high (>30°). In addition, presence of nystagmus or any ocular motility disorders was noted.
Hiding Heidi test was used to assess contrast sensitivity (CS). This test consists of a set of three cards with a smiling face printed on both sides at each level of contrast. The contrast levels are 100%, 25%, 10%, 5%, 2.5% and 1.25%.10 The test was presented in two-alternative forced choice method with simultaneous presentation of two cards; one with face and the other blank. Verbal children were asked to point to which of the two cards had the face. Objective eye fixation pattern was observed for non-verbal ones. The lowest contrast card that generated a response either verbally or with eye fixation preference was noted. Distance fixation cycloplegic refraction was carried out in all children. The criterion for determining significant refractive error was <−0.50 Down syndrome (DS) for myopia, >+1.00 DS for hyperopia, ≥1.00 D for astigmatism and ≥1.00 D for anisometropia.
Anterior segment evaluation was carried out with the use of a portable handheld slit lamp. Posterior segment examination was carried out with the help of direct ophthalmoscopy. Presence of any abnormal anterior or posterior segment findings was noted.
Methods used in the study were modified to suit the needs of the individual child. Use of interesting toys, flashing lights, positive reinforcement with stickers and gifts was applied to successfully complete the visual assessment. In addition, authors PA and JBS are highly skilled paediatric professionals who have >5 years of experience working with TD children and children with IDs.
Results
In total, 162 children were invited, out of which 150 were enrolled in the study, giving a consent rate of 92.6%. Twelve children were excluded as none of the components of visual assessment could be completed. All of these children were either reluctant or their parents did not provide consent to our assessments and were referred for further evaluation to the nearest eye hospital. Children with DS (23%), cerebral palsy (CP) (22%), developmental delay (21%) and autism (20%) contributed the majority of our study group. Other children had ID of unknown origin (5.5%), attention-deficit hyperactive disorder (3%) and others (5.5%).
Of the total children, 60% were females and the rest were males. The mean age±SD of children was 10.64±4.12 years. Most of the children (41%) were in the age group of 5–9 years and 36% in the group of 10–14 years. Only 3% of the children were <5 years of age. About 60% of the children had a history of previous ophthalmic examination based on the medical records.
Visual acuity
Fifty per cent of the children were assessed with Kay Picture test followed by Keeler Acuity Test (42%). The Snellen chart, an acuity test commonly used in adults, was successful only in 8% of the children. There was a statistically significant negative association between testability of VA test difficulty and the age of the children (χ2 test, χ2=45.80, df=30, p=0.03). This was in contrast to what we expect to observe in TD peers. In TD children, the testability of difficult acuity tests increases with increasing age. This analysis was supported by observing that Keeler Acuity Test, an objective measure of VA that is commonly used to assess preschoolers, was used in 40% of children >5 years of age.
The mean presenting logarithm of the minimum angle of resolution (logMAR) VA in the right eye was 0.42±0.28 (6/15). There was no statistically significant mean interocular difference in VA. Presenting VA of the better eye was considered to categorise VI, and the WHO guidelines11 were followed. According to these criteria, VA is classified as normal with no VI (VA better than or equal to 0.3 logMAR or 6/12 Snellen), mild VI (VA better than 6/12 and poorer than or equal to 6/18), moderate VI (VA poorer than 6/18 or equal 6/60), severe VI (VA 6/60–3/60), legally blind (VA 3/60—perception of light) and totally blind (no perception of light). Thirty per cent of children had normal or near normal VA (better than or equal to 0.3 logMAR or 6/12 Snellen), 44% had mild VI (poorer than 0.3 logMAR to equal to 0.5 logMAR or poorer than 6/12 to equal to 6/18) and 25% had moderate VI or worse (poorer than 0.5 logMAR or 6/18 Snellen). Severe VI or worse (poorer than 6/60 or 1.0 log MAR) was present in 3% of the children.
Refractive error
Fifty per cent of the eyes (40% of the children) had significant refractive errors according to our cut-off criteria. The range of refractive errors were from −9.00 to +5.00 D in the right eyes and −11.00 D to +5.00 D in the left eyes. Astigmatism was present in 21% of the eyes. Simple myopia and simple hyperopia each represented 15% of the total eyes. Six per cent of the children had anisometropia. Astigmatism was significantly higher in the DS and the other groups (p<0.05, Fisher's exact test) compared with the rest of the group. Hyperopia was significantly common in the CP group and myopia in the developmental delay group (p<0.05, Fisher's exact test). Myopia and astigmatism were equally prevalent in children with autism. Children found to have significant refractive errors were referred to the nearest eye hospital. Table 1 shows detailed refractive characteristics of our study children.
Distribution of types of refractive error according to groups
Table 2 shows that children who had refractive errors presented with significantly poor VA than children who were emmetropic (one-way analysis of variance (ANOVA), F=21.22, p<0.001). However, there was no significant difference in acuity among children with different types of refractive errors.
Mean presenting visual acuity in children with different refractive characteristics
Strabismus
Manifest strabismus was detected in 17% of the children. Among the children with strabismus, exotropia (52%) was slightly more prevalent than esotropia (48%). The magnitude of deviation was small in 74% of the children followed by moderate in 18% of the children. Only two children (7%) had high deviation.
Contrast sensitivity
The mean binocular log CS was 1.81±0.17 log units. The presence or absence of visual disorders did not make any significant change in the CS value (p>0.05). Among the four main groups, children with CP had the lowest CS score (1.73±0.21 log units). Normal value of CS for adults and children using Hiding Heidi (HH) is found to be 1.90. Mean CS values in our cohort were significantly below that of normal adults statistically (1.82 log units vs 1.90 log units) (one-sample t test, p<0.05); however, it was not considered clinically significant. Also, no significant difference was found in the CS values between groups (one-way ANOVA, p>0.05 for all) except between DS and CP where the values were significantly different (1.89 log units vs 1.73 log units, one-way AVOVA (post hoc) least significant difference p<0.05). And again, the difference was not considered clinically significant.
Other ocular findings:
Altogether 46% of the children had some forms of extraocular, anterior or posterior segment findings. Eyelid and adnexal disorders such as nasolacrimal duct obstruction, blepharitis, chalazion and ectropion combined together contributed morbidity in 24% of the children. Twelve per cent of the children presented with conjunctivitis. Two children had cataract and one child had keratoconus. Children with DS had higher prevalence of external ocular disorders, which was consistent with previous studies. This was followed by children with CP. Suspicious glaucomatous optic disc was present is 6% of the children and retinitis pigmentosa was present in one child. Nystamgus was present in one child. We were surprised to learn that none of these eye conditions were mentioned in the medical records and neither were they detected earlier. This provides us with strong evidence that teachers and parents of children with ID are unaware of visual disorders in these children.
Discussion
Our study is one among the few studies done in developing countries that depict the burden of oculo-visual status in children with IDs. Our study showed that 40% of the children had not had any ophthalmic examination in their lifetime. This finding was disappointing for us, but a possible explanation for these results may be the lack of national vision screening guidelines for children in Nepal. We believe that this situation may have led to a lot of oculo-visual disorders left undetected during childhood not only in children with ID but also in their TD peers.
In the current study, we were able to assess visual function in all of the children using different tests. We were not able to perform age-appropriate tests in all of the children; however, practical experience in administering vision tests was applied. We sought help from the teachers or parents whenever required to successfully complete the assessment in some of the children. Our finding is in accordance with a study done by Coulter et al12 in determining the testability of vision tests in children with autism. We agree with their view that children with ID can perform most of the vision tests if appropriate visual, communicative and sensory supports are incorporated in the testing protocol. In our study, administration of different vision tests depended on the cognitive ability and behavioural/verbal response of the child. However, it was unanticipated that 25% of the children were visually impaired according to the WHO criteria of VI and blindness. Furthermore, if we consider VI as VA poor than 6/12 (0.3 logMAR), 57% of the children fell into the VI group. This percentage is considerably high compared with the TD peers.9 Among the five (3%) children who were either severely visual impaired or legally blind, three of them had uncorrected high myopia and for the rest two, one had hyperopia with strabismus and the other had nystagmus. The form of blindness in at least four out of five children was avoidable if they were detected early. Moreover, the majority of children in study group who had reduced VA had uncorrected refractive error. This finding has important implications for developing vision care guidelines in younger children and more specifically targeted to children with ID. Presence of a wide range of refractive errors further supports the idea of emmetropisation being hampered in children with ID.13 The prevalence of refractive error in our group is consistent with the published literature.2–7 ,13 ,14 Children with ID have high prevalence of binocular vision disorders. Our finding of strabismus in these children was in accordance with few previous studies. No convincing reasons for the higher prevalence (17%) of strabismus in these children have been postulated; however, in some conditions such as CP, the location of cerebral lesion may play a role in manifestation of strabismic disorders. Depending upon the characteristics of strabismus and the severity of the disability, researchers have found variable outcomes of strabismus surgery in these children. Setting aside the gain in binocular vision, if detected early and treated promptly, good VA may be achieved at least in some of these children using the same amblyopia treatment regimen used for TD children. This is the first study that assessed CS in a variety of children with ID. Even though there was not a significant difference in the binocular CS values with normative population, our findings show that, among the groups, children with CP had the poorest CS value. This study has been unable to demonstrate that children with ID have poor CS. It is difficult to explain this result, but it might be related to the use of Hiding Heidi CS that has been found to be insensitive in detecting subtle CS deficits. Hence, from our findings we do not recommend Hiding Heidi for detecting CS at least in children with ID if they are to be used for diagnostic purposes. Inability of the Hiding Heidi test to detect subtle CS has been established by few other studies as well.15 ,16 Even though the face stimulus used in Hiding Heidi attracts the attention of children, the floor effect of this test makes it unsuitable to determine the true threshold for research purposes.
Various other ocular abnormalities were also prevalent in our study group. Presence of considerable percentage of eyelid and infectious disorders such as blepharitis, nasolacrimal duct obstruction, chalazion and conjunctivitis may signify that ocular hygiene is not sufficient in these children. Moreover, some of these children have been found to have poor immunity from birth, which could be another reason for this finding.17 Presence of cataract and keratoconus is not a surprising finding in these children, which is consistent with previous studies.6 ,7 Although treating cataract has been relatively successful in these children, managing keratoconus is extremely difficult.
We were surprised to learn that the genetic conditions such as retinitis pigmentosa and keratoconus that we detected during our examination were neither mentioned in the medical records nor were detected earlier. This provides us with strong evidence that teachers, parents and even the health professionals taking care of these children are unaware of visual disorders in these children.
Working hand in hand with various paediatric professionals will improve the outcome and lead to improved quality of life in these children. A scoping review by Williams et al18 on available treatment modalities for children with neurodevelopmental and visual disabilities concluded that there is still a gap in the evidence on treating children with vision and neurodevelopmental disorders. However, the study has put forward some considerations that all children with neurodevelopmental disabilities should have their eyes checked for near and distance. It is also postulated that it is unclear whether other interventions such as environmental modification and vision training are successful in these children as there is lack of sufficient evidence. Furthermore, a study conducted by Das et al19 has provided us strong evidence that children with special needs require vision assessments. There are no studies in the literature whether improved visual function has any effect on other skills such as cognitive and motor. Further studies that take these variables into account will need to be undertaken to determine the relationship.
Conclusion
The present study confirms previous findings and contributes additional evidence that suggests children with ID have high prevalence of oculo-visual disorders. Our study also concludes that there is a considerably high prevalence of VI and very low accessibility of ophthalmic care to children with ID in Nepal. There is a pressing need to raise awareness among parents and paediatric professionals regarding the presence of oculo-visual disorders in children with ID. We believe that preparation and immediate implementation of an appropriate vision screening guidelines for younger children along with special considerations for children with ID could presumably reduce the prevalence of oculo-visual disorders in all younger children of Nepal.
References
Footnotes
Competing interests None declared.
Patient consent Consent obtained from the parents.
Ethics approval The study was approved by the Institutional Review Board, Institute of Medicine, Tribhuvan University, Kathmandu, Nepal.
Provenance and peer review Not commissioned; externally peer reviewed.