A C T A 0 P H T H A L M 0 L O G I C A 70 (1992) 111-114

Keratoconus in the mentally retarded

Olav H. Haugen

Department of Ophthalmology, University of Bergen, Norway

Abstract. Among 212 institutionalized mentally re- tarded, there were 16 patients with keratoconus (7.5%). Eight of the keratoconus cases were unilateral. The possible role of eye rubbing as well as other etiological factors are discussed.

Key words: keratoconus - mental retardation - Down’s syndrome.

There is a well known association between kerato- conus and mental retardation. While the pre- valence of keratoconus in a normal population is about 1/1000, several authors have reported a pre- valence of 5-15% among the mentally retarded. In particular, the increased frequency of keratoconus among patients with Down’s syndrome has been well documented since the first report by Rados (1948). The exact cause of this increased pre- valence of keratoconus in mentally retarded people is not known. Genetic alterations leading to structural or biochemical changes in the cornea, and extensive eye rubbing are the two main hypo- theses. In this paper the prevalence of keratoconus in an institution for mentally retarded people is re- ported together with other ophthalmological fea- tures among this group of patients.

Material and Methods

During March-April 1989 212 persons (92 females and 120 males) were examined. This comprised all the inhabitants of the institution. The mean age of the patients was 46 years (range 15-90). The causes of mental retardation are listed in Table 1. Prior to examination, the staff at the institution answered a

questionnaire for each patient, giving their im- pression of the patients’ visual function and inter- est in ‘visual’ activities, such as TV, cartoons and newspapers. All the patients underwent an exam- ination including the position and motility of the eyes, a thorough inspection of the anterior seg- ment, indirect ophthalmoscopy and retinoscopy in cycloplegia. Different tests were used to assess the visual acuity (Table 2).

The diagnosis of keratoconus was based upon inspection of the cornea with focal illumination, slit-lamp examination (whenever possible), the presence of an abnormal red reflex indicative of keratoconus and retinoscopy in cycloplegia (ir- regular astigmatism). All examinations were car- ried out at the institution by the author. Kerato- metry was not available.

The keratoconus patients were examined with regard to structural changes of the iris, especially translucency, using paraxial illumination through the dilated pupil with the slit-lamp. Diascleral transillumination was not possible to perform.

Six years prior to this study, patient no. 1 (Table 3) underwent a penetrating keratoplasty in the right eye. The corneal transplant remained trans- parent for 4 years, thereafter it was thickened and gradually opacified, probably due to trauma. None of the other keratoconus patients had undergone corneal surgery.

To evaluate the possible role of eye rubbing in the etiology of keratoconus, a quantification of the eye rubbing was estimated by the institution staff both in the keratoconw patients and in a control group. Mantel-Haenszel’s test was applied for stat- istical analyses.

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Diagnosis patients Visual acuity test

Down’s syndrome Neonatal asphyxia CNS-infection in infancy Hydrocephalus Prematurity Microcephalus Head trauma Metabolic disease

- Felling‘s disease - Galactosemia - Cretinism - Spielmeyer-Vogt’s disease

Intracranial haemorrhage Prenatal infection Identified clinical syndromes Kernicterus Unknown

No. of patients

30 15 9 6 5 5 4 4

1 1 1 1

3 3 2 1

125

Patient no.

Total 212

Kerato- Ability Staff’s general conus to impression Visual Visual Therapeutic

unilateral/ commu- of visual tests2 acuityg measurements Sex Age Diagnosis

bilateral nicate’ function

I

Chart tests (Snellen, 0sterberg) 104 57

Fixation pattern/follow movements 17

Unable to test 34

Total 212

Non-symbol test (smarties at 1 m, ‘hundreds-and- thousands’)

(hand-doll)

Results

Prevalence of keratoconus Keratoconus was found in 16 (6 males and 10 fe- males) of the 212 inhabitants (7.5%). Clinical infor- mation about these patients is summarized in Table 3. The keratoconus was unilateral in 8 pa-

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16

F 60 M 41 M 30 M 51 M 36 F 31 F 82 M 32 F 50 M 69 M 46 M 46 M 52 F 32 F 74 F 47

Unknown Unknown Unknown Down Unknown Down

Down Unknown Unknown Unknown Down Down Unknown Down Unknown

*

bilateral bilateral bilateral bilateral bilateral unilateral unilateral bilateral unilateral unilateral bilateral bilateral unilateral unilateral unilateral unilateral

1 2 3 3 3 3 2 2 3 3 2 2 3 1 3 1

impaired normal impaired normal normal impaired impaired impaired normal uncertain impaired impaired impaired normal impaired normal

1 1 2 4 3 2 1 1 2 4 2 1 3 1 3 1

2 1 2 0 0 2 1 2 2 0 2 2 3 1 4 1

none glasses epikeratophakia O.S.

none keratoplasty 0.d. glasses glasses epikeratophakia 0.d. none none epikeratophakia O.S.

none none none ** none

’ 1 =normal language, 2 =single words/signs, 3 =no language. ‘ 1 =chart test (Snellen or asterberg), 2 = non-symbol tests (smarties, ‘hundred-and-thousands’),

3=fixation pattern, follow movements using a hand doll, 4=unable to evaluate. 1 = 2 6/18, 2 = 6/24-6/60, 3 = 6/60 - cf. 1 m, 4 = cf. 1 m - cf. ad oc., 5 =light perception, 6 = amaurosis, 0 =impossible to classify. * Intracranial haemorrhage. ** Considered for cataract extraction, but refuse.

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tients, bilateral in 8. Six of the patients had Down’s syndrome. Hence, the prevalence of keratoconus among the 30 patients at the institution with Down’s syndrome was 20%. Ten of the 182 mentally retarded without Down’s syndrome (5.5%) had ker- atoconus. One of these patients had a history of in- tracranial haemorrhage at the age of one year, while the causes of mental retardation in the re- maining 9 patients were unknown. A chromosome analysis of all the non-Down’s syndrome keratoco- nus patients showed a normal karyotype. Table 4 shows the refraction of the fellow eye in the unilat- eral cases.

Patient no.

Keratoconus Refraction eye (R/L) of the fellow eye

6 7 9

10 13 14 15 16

Normal (Yo)

0”-4.5+5 0”-3.0--8 Emmetropia 60”- 1 .O- 1 .0 impossible due to cataract+l.O +1.0 impossible due to cataract 160“-1.0

Often Very often ( 0 4 (Yo)

Structural changes of the iris One of the keratoconus patients without Down’s syndrome had a bilateral speckling of the iris col- our. Three of the 6 keratoconus patients with Down’s syndrome had Brush field spots. Apart from these changes, the iris appeared normal in the keratoconus patients as judged with focal il- lumination and/or slit-lamp examination. In 6 pa- tients it was possible to examine for translucency of the iris, but with negative result.

Eye rubbing Table 5 shows that the keratoconus patients really did rub their eyes more often than the other men- tally retarded, both among patients with and with- out Down’s syndrome (P= 0.008 in both groups).

Treatment Four of the bilateral keratoconus patients were operated. Epikeratophakia was performed in three cases, while a penetrating keratoplasty was done in the fourth patient.

Discussion The prevalence of keratoconus among patients with Down’s syndrome has usually been reported to be 2-15% (Skeller & 0ster 1951; Cullen & Butler 1963; Levy 1984; Shapiro & France 1985; Riise 1986; Prokesova et al. 1990). Thus, the prevalence of 20% in our material is high compared with ear- lier reports. However, Jacobson (1988) has re- ported an exceptionally high prevalence of kerato- conus (30%) among 50 patients with Down’s syn- drome, but of the above mentioned authors, only Jacobson performed keratometry in a number of her patients. This fact could in part explain the high figure of keratoconus in her material.

Our study also revealed a remarkably high pre- valence (5.5%) of keratoconus among the mentally retarded without Down’s syndrome. This could in- dicate a common, but yet unknown cause for the mental retardation and the corneal defect.

Table 5. Frequency of eye rubbing in 46 mentally retarded patients.

8 Acta Ophthal. 70.1 113

It is interesting that pathology of the iris and the pupil has been reported in association with kerato- conus (Urrets-Zavalia 1963; Bertelsen & Seim 1974; Davies & Ruben 1975; Baumann & Insler 1985). Embryologically, the corneal endothelium, the cor- neal stroma and the iris stroma are derived from the same tissue, namely, the neural crest cells. Thus, it is not surprising that iris pathology may be encountered in keratoconus patients. In our ma- terial 6 of the 16 patients with keratoconus cooper- ated sufficiently to be examined for translucency of the iris, but this phenomenon could not be dem- onstrated.

Keratoconus is usually a bilateral disorder. With the exception of Walsh (1981), the prevalence of unilateral cases is generally estimated to be 10-15Yo (Amsler 1961; Ihalainen 1986). In contrast, 50% of the keratoconus cases in the present material were unilateral. In six of these unilateral cases the re- fractive state of the fellow eye could be assessed by retinoscopy, thus ensuring that these cases were truely unilateral. Eye rubbing occurred signifi- cantly more frequently in the keratoconus group than among the other mentally retarded patients. This may indicate an etiological significance of eye rubbing in the development of keratoconus in pa- tients both with and without Down’s syndrome. However, as commonly experienced during kera- toplastic surgery, the consistency and mechanical properties in the conical cornea in patients with Down’s syndrome, as well as in a number of other mentally retarded, appear to differ from those present in a ‘normal’ keratoconus cornea. Hence, the cornea of the mentally retarded patients is probably more vulnerable to mechanical trauma. Therfore, there is obviously not one single causal factor in the pathogenesis of keratoconus, but both genetic and environmental factors are probably of importance.

Acknowledgment

This study was carried out with financial support from Riksforeningen mot blindhet og svaksyn.

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Received on May 27th, 1991.

Author’s address:

Olav H. Haugen, Department of Ophthalmology, University of Bergen, N-5021 Bergen, Norway.

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