Analysis of the Profile of the Peripapillary Nerve Fiber Layer with the Heidelberg Retina Tomograph

Abstract

Abstract: : Purpose: Using the Heidelberg Retina Tomograph (HRT) many strategies have been developed for the evaluation of glaucomatous optic discs. However little attention has been paid to the analysis the peripapillary retina. This study determines if the topography of the peripapillary nerve fiber layer changes during the course of glaucoma. Methods: 40 eyes of 35 patients were investigated with the HRT. Normal and glaucomatous eyes were differentiated by static perimetry, IOP and discriminant function of the HRT software. Age and refraction were equally distributed among both groups. For analysis a circle with a diameter 4 mm was drawn around the optic disc and the profile of the retinal nerve fiber layer (RNFL) was evaluated. In addition the mean retinal height was measured and used as reference plane. Volumes below the reference plane were determined. In order to exclude the influence of the increased cupping in glaucoma patients cup volumes as determined by the standard HRT strategy were deducted. The resulting values were tested for significance by standard t-test. Results: Normal RNFL profiles showed a small elevation next to the optic disc. In contrast glaucomatous RNFL profiles are characterized by continous shallow slopes. Volume measurements below the reference plane in the control group showed a mean of 0.334 ± 0.165 mm³. Among glaucoma patients volume measurements were significantly increased (p<0.0001) to 1.419 ± 0.498 mm³. Conclusions: In glaucoma patients the profile of the peripapillary RNFL is significantly altered and characterized by a loss of the peripapillary elevation. The resulting strategy of quantification allows a clear detection of a glaucomatous configuration. Furthermore the strategy of using a defined circle is independent from the widely used standard reference plane and less dependent on the observer than the current technique of contour line drawing.

Keywords: imaging/image analysis: clinical • nerve fiber layer • optic disc