Astigmatism in patients with idiopathic congenital nystagmus.

PURPOSE

To evaluate the association between astigmatism and idiopathic congenital nystagmus (ICN) in infantile nystagmus syndrome (INS).

MATERIALS AND METHODS

We analysed refractive errors in a cohort of 488 consecutive patients with ICN (group A) and further compared the results obtained with those of 488 age-matched controls with no nystagmus (group B). Only the worst eye was considered for statistical analysis. All patients were stratified into the following age groups: 1 to 4 years (age group 1); 5 to 12 years (age group 2); and 13 years to 57 years (age group 3) (mean age: 29).

RESULTS

Three hundred and seventy patients (69.7 %) in group A and 269 patients (55,12 %) in group B had refractive errors. The types of refractive errors observed were: myopia, hyperopia (>0.50 dioptres) and astigmatism (>1.25 dioptres). Results in group A were as follows: 319 patients (65.37 %) were astigmatic, 34 (6.97 %) were hyperopic, and 17 (3.48 %) were myopic. Mean right-eye astigmatism was 2.72 dioptres, and mean left-eye astigmatism was 2.69 dioptres. Results in group B were as follows: 56 (11.47 %) were astigmatic, 165 (33.81) were hyperopic, and 48 (9.84) were myopic. Mean right-eye astigmatism was 2.05 dioptres, and mean left-eye astigmatism was 2.37 dioptres. The prevalence of astigmatism is greater, in the entire sample, for subjects from age groups 2 and 3 (p<0.005). It shows a tendency to increase with age for patients of group A and in age group 3 (p=0.009).

CONCLUSIONS

Astigmatism is more common in patients with ICN than in the general population (65.37 % vs 11.47 %) (p<0.001). Astigmatism increases with age, with a very high statistical significance in patients 13 years old and above (age group 3) when nystagmus is also present. Thus, nystagmus appears to be a predisposing factor for both the presence of astigmatism and the development with the age of high values of this refractive error. This findings should be taken into due account when considering visual dysfunctions in nystagmic patients.