Refraction and the axial length of the eyeball in patients with the optic disc drusen

Introduction
The aim of the study was to demonstrate the relationship between the optic disc drusen (ODD) and the axial length of the eyeball as well as refractive error.

Material and methods
We examined prospectively 40 patients with ODD, 18 men and 22 women, age range from 34 to 69 years. All subjects underwent full ophthalmic examination, visual field testing and color-coded duplex sonography of the ocular vessels. Refraction was determined with an autorefractometer (Topcon RM-8000B) and further refined subjectively. Spherical equivalent refraction was calculated as the spherical dioptre plus one half of the cylindrical dioptre. Axial lengths were measured with a Sonomed ultrasound scanner model E-Z Scan AB5500.

Results
Clinical signs were observed in 65% of the eyes with drusen, among them, 38% had symptoms of visual acuity loss and all had visual fields defects. There were 21 eyes (18 eyes with and 3 without drusen), with a recorded refractive error. Significant differences in hyperopia were observed between the eyes with and without drusen (p = 0.048). The rate of occurrence of myopia did not differ significantly between affected and unaffected eyes (p = 0.06). The mean spherical equivalent refraction and axial dimensions of the eye differed significantly among the groups of eyes with and without drusen (p<0.05). Significant differences in mean values of peak-systolic and end-diastolic velocities (p<0.001) as well as in the resistivity index (p = 0.047) were observed between eyes with and without drusen.

Conclusions
The optic disc drusen are often associated with shorter and hyperopic eyes. This anatomical conditions and vascular factors may contribute to pathogenesis of drusen.