Purpose Optic nerve drusen (OND) are acellular, calcified, laminated concretions of unknown etiology that form within the substance of the optic nerve head. OND may be visible on ophthalmoscopic exam (“visible drusen”), but some optic nerves harbor drusen that are not visible on ophthalmoscopy (“buried drusen”). Buried OND are best detected by ultrasonography. Peripheral visual field defects can be detected in 71-75% of eyes with OND and field loss may be sufficiently severe to cause significant visual disability. Some authors have contended that eyes with buried OND may have visual field defects that are more severe than eyes with visible OND. The purpose of this investigation was to study visual field defects and retinal nerve fiber layer (RNFL) damage in eyes with buried OND.
Methods This study was approved by the University of Utah and University of Minnesota Institutional Review Boards. All subjects underwent automated perimetry using the Humphrey Visual Field Analyzer. Visual field defects were defined in a manner similar to that used for the Normal Tension Glaucoma Study. Some eyes underwent optical coherence tomography (OCT) to evaluate the RNFL. OCT was performed on dilated eyes with a Zeiss Stratus 3000.
Results We evaluated 50 eyes from 35 subjects with buried OND. There were 12 males and 23 females. Ages ranged from 10 to 71 years old. Of these 50 eyes, only 3 eyes had visual field defects. The defects in these eyes were very mild, with a mean defect of -4.92 db. No subjects were symptomatic and no subjects had a loss of central visual acuity. None of the 17 eyes examined with OCT had any significant RNFL defects.
Conclusions Although the pathogenesis of visual field loss in OND is unknown, most authors believe that OND cause visual loss by damaging the ganglion cell axons. It is possible that buried OND are not only too small or too deep within the optic nerve to be visible, but also too small to cause detectable ganglion cell damage. Although the majority of patients with visible OND have visual field defects, our data suggest that if a patient with a visual field defect has buried OND, another source for the visual field defect should be sought.
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