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Prevalence of visual impairments in adults with cognitive and developmental disabilities in a sheltered workshop in Germany.

Abstract: Individuals with cognitive and developmental disabilities have a high probability of visual impairment. This study revealed the effects of deficits in the appropriate diagnosis of vision and medical treatment, as well as the lack of necessary refraction correction and support, specifically for adults with intellectual and developmental disabilities.


There have no been studies of the prevalence or type and severity of visual impairments (both blindness and low vision) in adults with cognitive disabilities in the Federal Republic of Germany to date. A literature review of research in Denmark, the Netherlands, and Great Britain points to a prevalence of 5% to 50% for this population (Evenhuis, Theunissen, Denkers, Verschuure, & Kemme, 2001; Van Splunder, Stilma, Bernsen, Arentz, & Evenhuis, 2003; Warburg, 2001) and leads to the assumption that a similar proportion of adults with cognitive and developmental disabilities in Germany would also have visual impairments that are often not diagnosed. A literature review also showed that people with Trisomy 21 have a high risk of ocular disorders (Down's Syndrome Medical Interest Group, 2005) and that the prevalence of individuals with a visual acuity of less than 20/40 (0.5) is increasing with age (Deremeik et al., 2007).

Undiagnosed visual impairments, untreated eye diseases, and insufficient correction of refractive errors may have direct medical consequences. Furthermore, there can be additional difficulties in the lives of individuals in this population because behavioral patterns are not appropriately interpreted and interventions specifically for visual impairments are not implemented. There is a danger that the goal of participation in social life and particularly in the employment sector will be limited in individuals with cognitive disabilities and undiagnosed visual impairment.

The study


Adults with cognitive and developmental disabilities in Germany work mainly in sheltered workshops for individuals with disabilities and live in small group homes or dormitories, with their families, or independently in the community. The study presented here evaluated the functional vision of 241 employees with cognitive disabilities in a sheltered workshop for individuals with cognitive and developmental disabilities in Glueckstadt, northern Germany. This workshop has two departments: the manufacturing and vocational training department for employees who need intermittent, limited, or extensive support (those with mild, moderate, or severe cognitive disabilities) and the day-support center, with services for individuals with extensive or pervasive needs (severe and pervasive cognitive disabilities). The 241 persons shared the characteristics of an almost complete sample in the two departments of the sheltered workshop; only those who worked outside the workshop in the community or who were ill for a long period of time were not included.

To estimate the degree of intellectual and developmental disability of the participants, we used the classification of the American Association on Intellectual Disabilities. This classification is based on the needs for support of the individual (Luckasson et al., 2002). For 53.5% of the employees, the cause of cognitive and developmental disabilities was unknown to the staff of the workshop. Early childhood brain damage was diagnosed for 14.5%; Trisomy 21 was the cause of intellectual disability for 12.9%; and other causes, such as "accident," "meningitis," or "brain tumor," were mentioned for 19.1%.


The evaluation of functional vision was conducted in a room of the sheltered workshop by the first author (a low vision specialist and special education teacher of children who are visually impaired at the State Resource Center for the Visually Impaired in Schleswig) from September 2006 until April 2008. Following this evaluation, all individuals whose distance visual acuity was less than 20/40 (0.5), as well as individuals with a distance visual acuity of more than 20/40 but who had near visual acuity at least two logarithm steps lower or whose contrast sensitivity was impaired, were advised to set up an appointment with an ophthalmologist. Following the ophthalmologic examinations, the results were given to the workshop. An acuity measurement was repeated for those with a new correction for distance or near vision or both.



The classifications of visual impairments for the participants was based on the classifications of the World Health Organization (2007). The classification was made on the basis of binocular distance visual acuity or distance visual acuity of the better eye. Persons were classified as blind if their acuity was less than 20/400 (.05). Persons were classified as having low vision if their acuity was greater than 20/400 (.05) but less than 20/60 (0.3).

To differentiate among those in the group with acuities above 20/60 (0.3), an additional reference value was introduced: Those whose acuity was actually higher than 20/60 (0.3) but less than 20/40 (0.5) were classified as having reduced vision. All those who had acuities of higher than 20/40 (0.5) were classified as sighted.


The functional vision evaluations consisted of structured observations of visual attention (in daylight and in a darkened room), visual motor functions (fixation, tracking movement, and convergence), color and shape perception, distance and near visual acuity, magnification needs, binocular vision, contrast sensitivity, glare sensitivity, and visual field (Arntzen Andrew, Groben, Henriksen, 2006). The data were entered by hand on structured sheets and then transcribed in SPSS (Version 15 for Windows) for further statistical processing. With the aid of descriptive statistics in SPSS, data on prevalence and distributions of data could be analyzed.

Distance visual acuity was--according to the degree of cognitive disability--tested binocularly with Lea numbers, Lea symbols, or Lea gratings. Preferential looking gratings measure grating acuity. These behavioral methods tend to overestimate visual acuity because they estimate acuity only in the horizontal meridian and because there is no requirement for interpretation and less "visual crowding." On the other hand, recognition acuity is measured with letters, numbers, or symbolic pictures. Considering the lack of alternatives and practicality, both categories of acuity were viewed as equal. Grating acuity was measured with persons with severe disabilities only if it was not possible to use optotypes. Since the attention of many individuals with cognitive disabilities diminishes during testing at long distances, distance measurements were taken at 3 meters (about 10 feet), rather than at 5 meters (about 16 feet).

Near visual acuity was tested binocularly with Lea line symbols at 40 centimeters (about 16 inches). For individuals with severe visual impairments, the testing distance was adjusted accordingly, and the acuity was converted.

Contrast sensitivity was tested, when possible, with the SZB-LCS-Test using Landolt rings. This test requires two visual acuity measurements, one using the high-contrast version and one using the low-contrast version. The low-contrast signs are on the back of the chart and are two lines bigger than the high-contrast signs. Persons without restrictions in contrast sensitivity will have a low contrast acuity that is about two lines poorer than their high-contrast acuity. The greater the loss of low-contrast acuity beyond two lines, the greater the person's loss of contrast sensitivity (Greer, 2004). In addition to this test, the Lea symbols low-contrast test and the Hiding Heidi Test were also used. All symbols of the Lea Symbol Test have the same size but vary in contrast. The Hiding Heidi Test is a nonverbal preferential looking test that can be applied well with individuals with severe disabilities. To compare the three tests, we introduced three levels of contrast sensitivity for gathering data:

Group 1: Normal contrast vision (the group corresponds to the level up to -2 in the SZB-LCS-Test; in the Hiding Heidi Test and with Lea symbols, normal contrast vision is present when the weakest contrast (1.2%) can still be recognized.

Group 2: Limited contrast vision (SZB-LCS-Test: -3 and -4; Hiding Heidi and Lea symbols: recognition threshold equal to or greater than 2.5%).

Group 3: Extremely limited contrast vision (SZB-LCS-Test: above -4; Hiding Heidi and Lea Symbols: recognition threshold equal to or greater than 10%).

An additional evaluation of the visual field was conducted with the Nef Funnel or the confrontation method only in cases in which the ophthalmologist's report gave reason to believe that there might be defective areas in the visual field. Measurement of the visual field (by Goldmann perimetry or computer perimetry), which is done in an ophthalmologist' s office, is relevant only if the person being examined cooperates well. The determination of the visual field with the Nef Funnel is suitable for locating absolute defective areas in the central visual field, but does not locate any relative or peripheral visual field limitations. With the confrontation method, a rough estimate of the visual field is possible, and defective areas in the periphery can be determined. However, scotoma or relative defects cannot be measured. The degree of cooperation during the evaluation was rated "excellent" (the evaluation could be completed in its entirety), "good" (the evaluation could be completed with the exception of one item), "average" (the evaluation could be completed with the exception of two items), and "poor" (more than two items could not be evaluated).

Communication with persons who could not speak was conducted with the support of sign language or by the association of like symbols. Persons with corrective eyeglasses wore their eyeglasses during the evaluation, with the exception of those who had lost or thrown away their eyeglasses or who never brought them to the workshop.



A total of 241 persons in the workshop were evaluated: 27 (11%) from the day-support center and 214 (89%) from the manufacturing department. Their support needs were distributed as follows: 13% had an intermittent need for support, 53% had a limited need, 22% had an extensive need, and 12% had a pervasive need. The cooperation of 78% of the individuals who were evaluated could be called "excellent." For 15%, the cooperation was "good"; for 4%, it was "average"; and for 3%, it was "poor."


For 234 of the 241 individuals, it was possible to obtain an acuity or an acuity equivalent for distance vision (with 218, it was possible to measure recognition acuity, and with 16, it was possible to measure grating acuity). For 7 individuals, the acuity could be measured neither with symbols nor with grating patterns because they reacted anxiously, aggressively, or with autoaggression to any kind of request.

For 22% of the 234 persons, distance visual acuity of 20/60 (0.3) or less was measured. There were 6 individuals who were blind in this group. For 19%, acuity was above 20/60 (0.3) but less than 20/40 (0.5), and for 59%, an acuity of more than 20/40 (0.5) could be measured. In summary, more than 40% of the individuals had distance visual acuity greater than 20/40 (0.5). The distribution of distance visual acuity is presented in Table 1. It shows that the probability of visual impairment increases in individuals who attend the day-support center and have severe and pervasive cognitive disabilities.


For 87% (209 persons) of the individuals, near visual acuity could be measured. Analogous to the dependence of near visual acuity on age, near visual acuities obtained in the sample were distributed differently within different age groups. Near visual acuity continuously diminished across the age groups up to 35 years, 36-45 years, and older than 45 years (see Table 2).

Correction of presbyopia and accommodation problems

For the 56 persons who were older than 45 years, near visual acuity could be measured. Of this group, 64% had no correction for near vision, although their near visual acuity was lower than their distance visual acuity, and 20% had a correction for near vision, either as bifocal or single-strength eyeglasses. The remaining 16% either had sufficiently good near vision acuity (in some cases achieved on the basis of myopia) or rejected a correction in any form.

Furthermore, many individuals who were younger than age 36 had near visual acuity that was lower than their distance visual acuity. Accommodation problems seem to occur often and at a young age in individuals with cognitive and developmental disabilities, since a large number of persons have eye conditions (such as hardening of the crystalline lens in individuals who are developing cataracts) that cause reduced accommodative abilities. Individuals with Trisomy 21 may also have insufficient accommodative abilities at a young age.

Improvement with new correction

Of the 99 persons who consulted an ophthalmologist following the evaluation, 16 were prescribed new corrective eyeglasses. For 56% of those with a modified correction, there was an improvement in distance visual acuity of at least one logarithmical step (or one line on the acuity chart); for 1 person, distance visual acuity improved seven logarithmical steps. For 81%, near visual acuity improved with the new correction by at least one logarithmical step; for 1 person, it improved by nine logarithmical steps.

Three percent of those who had distance visual acuity of less than 20/60 (0.3) at the beginning of the project had a visual acuity of more than 20/60 (0.3) with the new correction. In some cases, it was just a slight improvement from 20/60 to 15/60 (0.3 to 0.4), which is only one line on the acuity chart; in other cases, it was a considerable improvement of seven lines (20/80 to 20/16 or 0.25 to 1.25). The total number of individuals with visual impairments decreased from 22% to 19% from the beginning of the project to the end.

Distribution of visual impairments and eye diseases

Visual impairments (distance visual acuity of less than or equal to 20/60 or 0.3) occurred in the group with Trisomy 21 with the most prevalence (52%), followed by 38% in the group with early childhood brain damage, and 27% in the group with other causes. For those whose intellectual disability had an unknown cause, the proportion was 9% (see Table 3).

For the analysis of the prevalence of eye diseases, the reports of the ophthalmologists for 97 persons were used. For the statistics, only those eye diseases were reported that were mentioned at least twice. In some cases, the report did not mention a specific disorder that leads to a functional loss.

For 33% of the group (except persons with Trisomy 21), amblyopia was diagnosed. Also diagnosed were cataract, both surgically removed and not removed (19%); nystagmus (10%); keratoconus (1%); optic atrophy (6%); and glaucoma (4%). For those with Trisomy 21, the prevalence of various eye disorders was observed separately. Cataract and keratoconus occurred in this group particularly frequently. Although cataracts were diagnosed for 19% and keratoconus was diagnosed for 1% in the rest of the group, the proportion in the group with Trisomy 21 who had cataract was 58%, and the proportion with keratoconus was 17% (see Table 4).


Contrast sensitivity could be measured in 222 persons. For 28 individuals (13%), limited contrast sensitivity was diagnosed, and for 20 individuals (9%), extremely limited contrast sensitivity was diagnosed. Limitations in contrast sensitivity and diminished acuity frequently go together. In the group with distance visual acuity of 20/60 (0.3) or less, 21% had limited and 39% extremely limited contrast sensitivity. One must also pay particular attention to the group with visual acuity between 20/60 and 20/40 (0.3-0.5). In this group, 24% had limited and 5% had extremely limited contrast vision (see Table 5).



It is difficult to compare the findings of the present study with those of other investigations of adults with cognitive and developmental disabilities, since the definitions of vision loss that are applied vary. Woodhouse, Griffiths, and Gedling (2000) examined 154 persons in Wales and described their vision as "normal" if their distance visual acuity was higher than 20/32 (0.6). On the basis of this threshold value, they found lower-than-average acuities for 63% of the persons who were tested. In our study, the threshold value for limited vision was set at 20/40 (0.5) for distance visual acuity. The proportion of individuals who had acuities below this threshold value in our study amounted to 40% without a new correction at the beginning of the project and 37% without a new correction at the end.

In comparison with the investigation by Warburg (2001), in which 16% of 961 adults with cognitive disabilities in Denmark were visually impaired (less than 20/60 or 0.3), the proportion of individuals in our study was 19% (with a new correction). However, the proportion in our study was a little lower than that in Van Splunder et al.'s (2003) study, in which 21% in a group of 900 adults with cognitive disabilities in the Netherlands were visually impaired.

The results of our study confirm the results of Evenhuis et al. (2001) and Van Splunder et al. (2003), which stated that visual impairment occurs more frequently in persons with severe and most severe disabilities than in other groups. Furthermore, as in the study by Evenhuis, Mul, Lemaire, and de Wijs (1997), we found that the risk of visual impairment is higher for persons with Trisomy 21 and persons older than age 50.

The causes of vision loss apart from congenital and acquired visual impairments are untreated eye diseases and inadequate corrective eyeglasses. An additional problem is the refusal of some individuals to wear eyeglasses. Thus, the need for accompanying rehabilitation services is evident.


In Van Splunder et al.'s (2003) study, it was possible to measure near visual acuity for 51% of the persons who were evaluated using the Stycar test. In our study, Lea symbols were used successfully to obtain a near visual acuity for 86% of the participants. This finding can be seen as a further indication that Lea symbols are well suited not only for children, but for adults with cognitive and developmental disabilities.

The measurement of near visual acuity formed an important part of this study. In ophthalmological examinations for the general public older than age 45, the testing of near visual acuity is routine. The results of our study point out that the measurement of near visual acuity in older persons with cognitive and developmental disabilities should not be taken for granted. They also show that for many younger persons, the testing of near visual acuity is important. Of 81 individuals younger than 36 years, 31% had a near visual acuity lower than their distance visual acuity. Accommodation problems, which evidently occur frequently in many younger individuals with cognitive and developmental disabilities, can be assumed to be the reason for this result. Testing of near visual acuity should, therefore, be routinely incorporated into ophthalmological examinations for persons with cognitive disabilities regardless of their age.

It is speculated that the name "reading glasses" may lead to a situation in which eyeglasses for near vision are not prescribed because the person has not learned to read. For individuals with cognitive and developmental disabilities who cannot read, eyeglasses for near vision are still a prerequisite for many activities of daily living.

The treatment of eye diseases and the correction of ametropia were, in this study, the responsibility of the individuals' ophthalmologists. If eyeglasses for near vision were prescribed, they were usually another pair of eyeglasses (in addition to those for distance vision), rather than bifocals. Individuals with cognitive disabilities are often challenged with two pairs of eyeglasses, since they cannot always determine which ones should be used in which situation. Thus, one could observe that some individuals wore their near-vision glasses all day even if they had blurry vision in the distance. With specific instruction, many of these persons could be taught to wear and use bifocals.

On the other hand, the use of bifocals can be difficult for people with central scotomas and eccentric viewing. These persons must turn their eye to position the visual image on the part of the intact retina closest to the macula. Doing so can be easier and more effective when using two pairs of single-strength eyeglasses, since a larger area for viewing is needed, and the area for distance and near vision in bifocals may be too small. Nevertheless, it should not be taken for granted that individuals with cognitive disabilities know how to use two pairs of eyeglasses without specific instruction.

The visual impairment of 54% of the persons in our study was unknown to the staff of the sheltered workshop at the beginning of the project. Unrecognized visual impairments result in a loss of independence, competence, and quality of life for the persons concerned.


This study showed that a great number of adults with cognitive and developmental disabilities have reduced visual acuity and visual impairments. At the same time, the probability of receiving adequate treatment and the proper refractive correction is obviously lower for them than for the general population. It is also evident that vision assessment is possible in the majority of adults with cognitive and developmental disabilities.

Only through thorough interdisciplinary cooperation among ophthalmologists, optometrists, opticians, low vision specialists, and the staff of the sheltered workshop can a lasting improvement be made in the living situations of the individuals concerned. Furthermore, the implementation of selected interventions specific to visual impairment (see Degenhardt, 2003) in everyday routines should be a goal of future research. These interventions should be related to the general behavioral patterns of the staff in regard to individuals with visual impairments (for example, addressing them and announcing actions), to the setup of the individual workplace or the selection of the jobs to be carried out, and to the design and illumination of rooms (see, for example, Buser, 2006; Degenhardt & Hilgers, 2008; Henriksen, 2006). Conditions for learning individual skills specific to visual impairment must be made available, including learning how to handle eyeglasses (both bifocal and single strength) and other optical devices (such as a closed-circuit television) and training in orientation and mobility, daily living skills, and practical vocational skills.


Arntzen Andrew, T., Groben, F., & Henriksen, A. (2006). Assessment of functional vision in children with multiple disabilities. In A. Henriksen & C. Henriksen (Eds.), Focus MDVI--Development of expertise for teachers who do itinerant work for multiple disabled visually impaired children (Comenius Project of the European Community). Schleswig, Germany: State Resource Centre for the Visually Impaired.

Buser, F. (2006). Licht, Kontrast, Farbe: SZB Kurs [Light, contrast, color: SZB course]. Unpublished manuscript, St. Gallen, Switzerland: Schweizerischer Zentralverein fur das Blindenwesen [Swiss National Association for the Blind].

Degenhardt, S. (2003). Padagogische Intervention bei Beeintrachtigungen der visuellen Wahrnehmung [Educational intervention with impairments of vision]. In A. Leonhardt & F. B. Wember (Eds.), Grundfragen der Sonderpadagogik [Fundamental issues of special education] (pp. 376-398). Berlin: Weinheim.

Degenhardt, S., & Hilgers, F. (2008). Das funktionale Sehen--Diagnostik und Forderung aus blindenpadagogischer Perspektive [Functional vision--Diagnostic and support from the perspective of the education for the blind]. In H. Kaase & F. Serick (Eds.). Sechstes Symposium Licht und Gesundheit [Sixth Symposium on Light and Health] (pp. 70-82). Berlin, Germany: Technische Universitaet Berlin [Technical University of Berlin].

Deremeik, J., Bromann, A. T., Friedman, D., West, S. K., Massof, R., Park, W., et al. (2007). Low vision rehabilitation in a nursing home population: The SEEING Study. Journal of Visual Impairment & Blindness, 101, 701-714.

Down's Syndrome Medical Interest Group. (2005). Best medical surveillance essentials for people with Down's syndrome. Nottingham, England: Children's Centre. Retrieved from library/articles/guideline-vision-5.pdf

Evenbuis, H. M., Mul, M., Lemaire, E. K., & de Wijs, J. P. (1997). Diagnosis of sensory impairment in people with intellectual disability in general practice. Journal of Intellectual Disability Research, 41, 422-429.

Evenhuis, H. M., Theunissen, M., Denkers, I., Verschuure, H., & Kemme, H. (2001). Prevalence of visual and hearing impairment in a Dutch institutionalized population with intellectual disability. Journal of Intellectual Disability Research, 45, 457-464.

Greer, R. (2004). Evaluation methods and functional implications: Children and adults with visual impairments. In A. Hall-Lueck (Ed.), Functional vision: A practitioner's guide to evaluation and intervention (pp. 177-222). New York: AFB Press.

Henriksen, A. (2006). Using the results of the functional vision evaluation to structure the learning environment. In A. Henriksen & C. Henriksen (Eds.), Focus MDVI: Development of expertise for teachers who do itinerant work for multiple disabled visually impaired children (Comenius Project of the European Community) (pp. 54-68). Schleswig, Germany: State Resource Center for the Visually Impaired.

Luckasson, R., Borthwick-Duffy, S., Buntix, W. H. E., Coulter, D. L., Craig, E. M., Reeve, A., et al. (2002). Mental retardation: Definition, classification and systems of supports (10th ed.). Washington, DC: American Association on Mental Retardation.

Van Splunder, J., Stilma, J. S., Bernsen, R. M. D., Arentz, T. G. M. H. J., & Evenhuis, H. M. (2003). Refractive errors and visual impairment in 900 adults with intellectual disabilities in the Netherlands. Acta Ophthalmologica Scandinavica, 81, 123-130.

Warburg, M. (2001). Visual impairment in adult people with moderate, severe, and profound intellectual disability. Acta Ophthalmologica Scandinavica, 79, 450-454.

World Health Organization. (2007). ICD-10 International Statistical Classification of Diseases and Related Health Problems (10th revision, version for 2007). Geneva: Author. Retrieved from classifications/apps.icd/icdl0online

Woodhouse, J. M., Griffiths, C., & Gedling, A. (2000). The prevalence of ocular defects and the provision of eye care in adults with learning disabilities living in the community. Ophthalmology and Physiological Optics, 20, 79-89.

Anne Henriksen, M.Ed., low vision specialist and teacher of students who are visually impaired, State Resource Center for the Visually Impaired, Schleswig, Lutherstrasse 14, 24837 Schleswig, Germany; e-mail: <>. Sven Degenhardt, Ph.D., professor, Institute for Special Education, University of Hamburg, Sedanstrasse 19, 20146 Hamburg, Germany; e-mail: <>
Table 1
Percentage distribution of distance visual acuity in the two
departments of the workshop (N = 234).


Department <20/60 20/60-20/40 >20/40

Total 22 19 59
Manufacturing department (n = 211) 17 18 65
Day-support center (n = 23) 70 30 0

Table 2
Percentage distribution of near visual acuity by age (N = 209).

Age <20/60 20/60-20/40 20/40-20/20 >20/20

Up to 35 years (n = 82) 15 18 57 10
36-45 years (n = 71) 20 18 58 4
45 years and older 36 21 43 0
 (n = 56)

Table 3
Percentage distribution of visual acuity by causes of cognitive
disabilities (N = 234).

 Early childhood
 Trisomy 21 brain damage Other causes
Visual acuity (n = 31) (n = 35) (n = 46)

<20/60 52 38 27
20/60-20/40 19 37 24
20/40-20/20 29 25 40
>20/20 0 0 9

 Unknown causes
Visual acuity (n = 129)

<20/60 9
20/60-20/40 12
20/40-20/20 61
>20/20 18

Table 4
Percentage distribution of diagnosed eye
diseases: Trisomy 21 and the rest of the group
with ophthalmological reports (N = 97).

 Rest of the group Trisomy 21
Eye disease (n = 73) (n = 24)

Cataract 19 58
Amblyopia 33 29
Nystagmus 10 13
Keratoconus 1 17
Optic atrophy 6 0
Glaucoma 4 4

Table 5
Limitations of contrast sensitivity in the
different acuity groups (percentage; N = 222).


Visual acuity limited Limited Normal

<20/60 39 21 41
20/60-20/40 5 24 71
>20/40 0 8 92
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Article Details
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Author:Henriksen, Anne; Degenhardt, Sven
Publication:Journal of Visual Impairment & Blindness
Article Type:Report
Geographic Code:4EUGE
Date:Jul 1, 2009
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