LASER-SCANNING TOMOGRAPHY OF LOCALIZED NERVE-FIBER LAYER DEFECTS

Aims-Retinal nerve fibre layer photography is a well established metho d to qualitatively document early structural changes which might be in duced by primary open angle glaucoma. The aim was to analyse localised retinal nerve fibre layer (RNFL) defects in a new quantitative way wi th respect to surface topography, defect width, and surface reflectivi ty by means of the technique of confocal scanning laser tomography. Me thods-12 eyes of 12 patients with a localised RNFL defect documented i n RNFL photographs and a normal appearance of the optic disc were enro lled in the study. Using confocal laser scanning tomography (Heidelber g retina tomograph, HRT) a series of 32 optical section images from di fferent focal planes of the retina at the site of the RNFL defects wer e obtained. The optical section images, the reflectivity images, and t he topographic images were analysed regarding the visibility of the RN FL defects. The mean surface height and the reflectance at the sites o f the RNFL damage were measured and compared with the adjacent apparen tly normal retina. The width of the RNFL defect at 1 mm distance from the disc border was evaluated. Results-RNFL defects could be detected in nine of 12 reflectivity images (75%). Single optical section images displayed the RNFL defects in 12 of 12 eyes. The defect width ranged from 0.11 to 1.0 mm. In six of 12 eyes a surface depression (34 (SD 5) mu m; range 21-47 mu m) was present. The reflectance ratio ranged fro m 0.68 to 0.94 at the site of the RNFL defect. In eyes with a glaucoma tous scotoma in a 6 degrees grid visual field (VF), the defect width w as at least 0.25 mm. Surface depression and low reflectance ratio were found irrespective of the presence of a scotoma in the 6 degrees grid VF. Conclusion-The majority of localised RNFL defects can be detected in reflectivity images fi om laser scanning tomograms. Localised RNFL defects may be differentiated according to surface topography into th ose with and those without a measurable surface depression. A small bu t deep RNFL defect is not necessarily associated with a scotoma in rou tine 6 degrees grid VF static perimetry.