Refractive development in children with Down's syndrome: a population based, longitudinal study.

Abstract

Aims--To study the refractive development in children with Down's syndrome longitudinally.

Methods--An unselected population of 60 children with Down's syndrome was followed with repeated retinoscopies in cycloplegia for 2 years or more (follow up 55 (SD 23) months). Accommodation was assessed with dynamic retinoscopy.

Results--From longitudinal spherical equivalent values of the right eye, three main categories of refraction were defined: stable hypermetropia ([less than]1.5 D difference between the first and last visit) (n=34), increasing hypermetropia ("hypermetropic shift"; [greater than or equal to] 1.5 D difference) (n=11), and decreasing hypermetropia/development of myopia ("myopic shift"; [greater than or equal to] 1.5 D difference) (n=9). Patients with anisometropia (n=6) were evaluated separately. In the stable hypermetropia group three sublevels were chosen: low ([less than or equal to]+2.0 D at the last visit), moderate (+2.25 to + 4.0 D), and high ([greater than]+4.0 D). An accommodation weakness was found in 55% of the children. Accommodation weakness was significantly less frequent in the stable, low grade hypermetropia group (22%) than in all the other groups (p=0.008). The frequency of astigmatism [greater than or equal to]l.0 D at the last visit was 57%, the direction of axis being predominantly "with the rule." All the eyes with oblique astigmatism had a side specific direction of axis; the right eyes belonging to the 135[degrees] axis group and the left eyes to the 45[degrees] axis group.

Conclusion--A stable, low grade hypermetropia was significantly correlated with a normal accommodation. Accommodation weakness may be of aetiological importance to the high frequency of refractive errors encountered in patients with Down's syndrome. A striking right-left specificity in the oblique astigmatic eyes suggests that mechanical factors on the cornea from the upward slanting palpebral fissures may be a major aetiological factor in the astigmatism.

(Br J Ophthalmol 2001;85:714--719)

The increased frequency of refractive errors in individuals with Down's syndrome has been documented by many authors. [1-9] However, most studies have been based on selected populations. [1-6] In addition, all reports so far have been cross sectional studies.

Hoping to elucidate new aspects of this issue, we have studied the refractive development in an unselected Down's syndrome childhood population by repeated examinations during the past 10 years. To our knowledge, this is the first longitudinal study on refractive errors in children with Down's syndrome.

Subjects and methods

STUDY POPULATION

Seventy seven children with Down's syndrome born during the years 1988--99 in Hordaland County, Norway (population 416 000, annual births 6000), were referred from Vestlund Habilitation Resource Center to our department for an ophthalmological examination. This centre coordinates the habilitation of all Down's syndrome children in the county. To ensure a population based study design, the files of the regional laboratory for cytogenetics were examined. In this way we found 16 dropouts. Thus, the total number of patients with Down's syndrome born in our county during these years was 93, giving a mean annual incidence of 1.25 per 1000 live births (range 0.63--2.12).

Among the 16 dropouts, four had died and three had moved to other parts of the country. The other nine children were invited for an eye examination, which six of them attended. Valid data on previous refraction by other ophthalmologists could be obtained, and they were included in the study. Another six children moved to our region during the study period and were included in the study with successive examinations. Thus, 89 children with Down's syndrome born in the years 1988-99 were examined. Among these, 40 had their first examination during the first year of life (mean age at examination 7.1 (SD 3.0) months, range 3-12). Cross sectional data from these 40 infants will be presented separately.

Patients with follow up time [less than]2 years (n=29) were excluded from the longitudinal study. The group of children with Down's syndrome thus followed for 2 years with repeated eye examinations consisted of 60 children (30 girls and 30 boys). Mean follow up time was 55 (SD 23) months (range 24-115). With very few exceptions, all the examinations were done by one of the authors (OHH). In the whole longitudinal study group the mean age at the first examination was 21 (SD 14) months (range 3-61).

Informed consent was obtained from the parents, and the study was approved by the regional committee for medical research ethics.

REFRACTIVE MEASUREMENTS

Retinoscopy in cycloplegia was performed using cyclopentolate 1% eye drops twice 30 minutes before the examination. Astigmatism was recorded as minus cylinders. The axis of astigmatism was classified as follows: 180 (SD 15)[degrees] ("180[degrees] meridian" or "with the rule"), 90 (SD 15)[degrees] ("90[degrees] meridian" or "against the rule"), 16-74[degrees] ("45[degrees] meridian"), and 106-164[degrees] ("135[degrees] meridian").

To evaluate the axis of oblique astigmatism in a mentally normal population, we used the preoperative refractive data from the excimer laser clinic in our department. Only patients referred for primary, uncomplicated …