Evidence-Based Overview of Ophthalmic Disorders in Deaf Children.

Introduction

Deaf children are heavily dependent on their sense of vision to develop efficient communication skills and to explore the world around them. Any ophthalmic disorder may thus negatively impact on this process, especially if it is unrecognized in the early years of life when language acquisition is so critically important. These disorders may be correctable (such as myopia) or treatable (such as cataract), and their early identification is of the utmost importance to optimize language development (spoken, sign, or both) and develop social cognition. Deaf children may not complain about ophthalmic problems, which may thus remain undiagnosed for long periods of time. Those children with noncorrectable and nontreatable visual disorders, such as retinitis pigmentosa in Usher syndrome, require multiple environmental adaptations and appropriate support services and information. Access to relevant information and the acquisition of appropriate communication skills before the visual impairment becomes severe are crucially important for these children if they are to develop effective communication strategies. The work of overcoming the combination of vision and hearing loss needs to start early and has to continue throughout life. Children, adolescents, and adults need information on and access to rehabilitation programs that meet their needs and that are reworked as their personal situations change.

Individuals with hearing and visual problems are often poorly served because many professionals fail to understand the compounding impact of a dual sensory deficit. Deafblindness is not just the sum of deafness and blindness; it is a unique and entirely different condition. Therefore, professionals in the field of deafness need to familiarize themselves with the challenges presented by visual impairment; likewise, professionals in the field of visual impairment need to understand the impact of hearing loss.

From an international perspective, the dual sensory disorders have received little research attention. The research can be characterized by heterogeneity in subject population, methodology, and scientific ambition. This typically manifests itself in case studies, whether it concerns research on communication methods or behavior modification studies. Larger studies may exist but they are typically descriptive and not causally oriented. The lack of well-designed studies with clear objectives and strict criteria may have a significant negative effect on all areas of services provided to deaf and blind children.

Prevalence of ophthalmic disorders in Deaf children

Several studies reported the prevalence of ophthalmic disorders in deaf children. Most of them assessed deaf children in residential or day schools and they included children of all ages and causes. Some of the studies have reported all ophthalmic disorders together, whereas other studies have separated them into individual categories. There is wide variation in the tests used and in the definition of what constitutes an ophthalmic disorder. Most of the studies conclude that there is a very high prevalence of such conditions in deaf children.

These high rates of ocular abnormality in deaf children may be attributable to the following:

1. The sensory retina, the retinal pigment epithelium, and the neural portion of the optic nerve develop from neural ectoderm. This development starts during the fourth embryonic week. Elements of the inner ear (such as the labyrinth and the cochlea) develop from surface ectoderm during the same embryonic period. Any adverse environmental influences may thus cause developmental abnormalities affecting both the eye and the ear. Such environmental factors include toxic agents, drugs, infections (such as rubella virus, cytomegalovirus, and toxoplasma), and irradiation. When such injurious factors affect the fetus during the early embryonic period, major and sometimes multiple congenital lesions may result, because this is the most critical period for organogenesis.
2. Genetic factors may also play a part in the development of these abnormalities. Chromosomal abnormalities and gene mutations may profoundly affect the development of the eye and ear.
3. Prematurity, complications attributable to multiple births, anoxia, and infectious diseases (such as meningitis) may be injurious to both the eye and the ear, resulting in deafness and visual impairment.

How does the severity of the hearing loss Influence the ophthalmic disorder?

A study in 1992 found that children and young adults (age range, 6-22 yr) with deafness greater than 80 dB (Group A) had an overall higher prevalence of refractive errors compared with Group B children with deafness less than 80 dB and an overall higher prevalence of ocular abnormality, although these differences did not reach statistical significance.

However, there was a statistically significant increase in the prevalence of retinal abnormality in Group A compared with Group B. Most of this increase can be attributed to retinopathy consistent with rubella. The prevalence of this retinopathy in Group A was 13.4% compared to 6.1% in Group B. Of particular importance is the fact that over 50% of patients who had retinopathy consistent with rubella had not been identified as having a hearing loss attributable to rubella before the ophthalmic examination. Thus, ophthalmic examination may provide an invaluable pointer to the cause of deafness.

Prevalence of ophthalmic disorders and Deafness in children who have cognitive or learning difficulties

In studies of people with cognitive or learning difficulties living in institutions and in the community, the prevalences of visual and hearing impairments are found to be higher than in the general population. This is not surprising, because many cases of congenital and acquired childhood hearing and visual impairments, such as perinatal asphyxia, intrauterine infections, inborn errors of metabolism, meningitis, and brain tumors, may also cause cerebral damage.

Although adequate functioning of hearing and vision is important for psychomotor, cognitive, social, and emotional development, the diagnosis of visual or hearing impairment often remains unrecognized in individuals with learning difficulties. Delayed identification and management of visual and hearing impairments may influence an individual's ability to adapt to family and community life, may cause behavioral problems, and adversely influence cognitive development.

Therefore, early intervention and treatment are of paramount importance. Correction of refractive errors has been found to bring significant improvement even in motor behaviors. It is worth noting that visual impairment is seldom spontaneously mentioned by individuals with learning difficulties and deafness.

How does the cause of deafness influence the type of ophthalmic condition?

Although many studies have attempted to correlate the cause of deafness and the prevalence of ophthalmic problems in deaf children, very few had sample sizes adequate for valid conclusions. Armitage et al. did not find any significant difference in visual impairment between children with congenital and acquired deafness. However, the number of children with acquired deafness was too small (13 children) to allow for definite conclusions. The small number of children with acquired deafblindness is a common finding in the literature, especially after the introduction of rubella vaccination in the early 1970s. In 8% of congenitally deaf children, eye examination confirmed the suspected cause of deafness and, in a further 8%, actually identified the cause, which had not previously been suspected.

Rubella

Woodruff in 1986 studied 460 deaf children and assessed the differential effects of various causes of deafness on the prevalence of eye disorders. Congenital rubella caused blindness resulting from cataract and retinal abnormality affecting up to 64% of children. It also induced choroidal neovascularization, hemorrhage, and sudden loss of vision as late as 13 years of age. Congenital rubella was found to cause far more systemic and ocular damage than any other single cause of deafness and had the highest rate of astigmatism (up to 44% of affected children) when compared with congenital deafness, rhesus incompatibility, premature birth, meningitis, neonatal sepsis, and idiopathic deafness. With regard to myopia and hyperopia, the mean spherical refractive error in congenital rubella does not differ significantly from the other causes of deafness; however, meningitis had the highest mean spherical error, with a predilection for hyperopia rather than myopia.

Children deafened by rubella may develop late-onset conditions such as glaucoma (which usually remains symptom free until significant damage to the ophthalmic nerve has occurred), which suggests that serial assessments over time are necessary. Today in developed countries, congenital rubella is a relatively infrequent cause of deafness and ophthalmic disorders in children. This is attributable to the introduction in the early 1970s of systemic vaccination against rubella, which virtually eliminated the disease. In the 1960s, approximately one in five cases of sensorineural deafness was caused by congenital rubella. As many as 300 children per year were born with congenital deafness in the United Kingdom in the nonepidemic years, a figure that was far exceeded in the epidemic years. In 2001, only three cases of congenital rubella were reported in England, Scotland, and Wales. Increased global traveling and migration may adversely affect these figures in the future. Countries with compulsory vaccination and very high rates of compliance are protected, as between 85% and 88% of the population need to be immune to stop the spread of rubella.

EACH CHILD WITH AN OPHTHALMIC AND HEARING PROBLEM IS UNIQUE

The features that make a child with hearing and vision loss unique is the variation of vision and hearing problems (degree, field of vision/tunnel vision or peripheral or central scotomas, onset of hearing and vision problem, progressive or of acute onset). Acceptance in particular communities will be determined by the specific characteristics of each child. For example, a person who is blind and then becomes deaf may not be accepted by the deaf community. Besides, many deafblind children suffer from additional physical, emotional, and cognitive disorders. Fortnum and Davis, in a large, retrospective, epidemiologic study, found a prevalence of 39% of additional disorders in children with hearing loss of 40 dB or greater in their better hearing ear.

Each child's emotional needs within the family, school, or local environment may vary enormously, as may the degree of acceptance and integration. It is therefore evident that the possible combination of variables is large and makes every child unique and indicates that screening, management, education, and support should be flexible and tailored to the specific child's needs.

It is essential that each child is comprehensively assessed to achieve an accurate assessment of hearing and visual acuity. Every element of sensory potential must be recognized and exploited to the child's advantage. The smallest differential in sensory ability between two individuals may make all the difference between their levels of functioning. Therefore, precise assessment of these children and tailored correction of rehabilitation strategies are of major importance in improving their quality of life and helping them reach their full potential.

Close cooperation across various professionals is vitally important, whether this concerns the provision of spectacles, hearing aids, surgical procedures, cochlear implants, balance rehabilitation, or psychological support. This is particularly important during the school years, when access to a very challenging and varied educational curriculum is so important to realizing a child's full potential.

CONCLUSIONS AND RECOMMENDATIONS

1. The overall quality of evidence in the literature concerning deaf children and their ophthalmic problems is very low and this highlights the need for well-designed studies exploring epidemiology, assessment methods, screening, outcomes, and management. Moreover, studies are needed to explore the ways professionals should work with deafblind children and their families.

2. There is a high prevalence of ophthalmic problems in deaf children. Approximately 40 to 60% of them have one or more ophthalmic problems that may remain undetected for years.

3. Ophthalmic problems in deaf children have a serious impact in the acquisition of communication skills, as deaf children rely partly or totally on their sense of vision to explore their world.

4. Screening of ophthalmic problems in hearing children remains a topic of debate, as cost-effectiveness has been seriously questioned.

5. Concerns regarding the effectiveness of screening for ophthalmic problems in deaf children are less valid because the prevalence of ophthalmic problems in these children is high and the importance of vision to their development of communication skills.

6. Specialist ophthalmic examination should be carried out as soon as the diagnosis of deafness is confirmed irrespective of age and may need to be repeated at intervals after diagnosis.

7. Families should be informed about the nature of the screening process in discussion with the relevant professionals. Appropriate information should be available in a range of formats and in different community languages.

8. Professionals administering the tests should be familiar with the needs of deaf children with ophthalmic problems and should be sensitive to the communication needs of the child, especially when undertaking behavioral testing where their collaboration is needed. Provision of family friendly services is of paramount importance.

9. Although orthoptists can perform the majority of psychophysical tests (e.g., visual and stereo acuity tests, ocular motility tests), a comprehensive ophthalmologic assessment by slit-lamp biomicroscopy, streak retinoscopy, direct and indirect ophthalmoscopy, intraocular pressure measurement, and so forth, will be required. Electrophysiologic testing to help identification of Usher syndrome may be required.

10. Serial hearing assessments of children with dual sensory deficits are needed to monitor hearing thresholds, to optimize hearing aid use, and to ensure timely referral for cochlear implantation for those who need it.