The Heidelberg Retinal Tomograph or HRT is a safe, non-invasive confocal scanning laser imaging device that can be used to obtain three-dimensional images of the optic nerve head and retina in the posterior segment. The HRT software analyzes height changes or differences of the optic nerve head and is becoming an essential piece of equipment in diagnosing early glaucoma and monitoring the progression of glaucoma (as well as evaluating macular holes or edema).
The HRT works by focusing a confocal diode laser beam with mirrors on the retina and the nerve head. It records the perfectly focused reflected light of the laser beam at over 65,000 points. This process is very rapid and requires only 1.6 seconds to acquire all of the needed images. It stores 32 two-dimensional reflectance patterns and then combines them in a “layer-by-layer” fashion to make a three-dimensional image of the optic nerve head. This makes a topographical map of each patient’s nerve head showing both height and depression with an accuracy of 20 microns at each of the points. The field of view can be adjusted to 10 X 10, 15 X 15, or 20 X 20 degrees and the patient does not need to be dilated.
The HRT software is specially designed to analyze the data and produce a stereometric map, detecting subtle changes in height and distances of the retina and optic nerve head. The HRT analysis provides disc area, cup and rim area, cup and rim volume, mean and maximum cup depth, three-dimensional shape of the cup, and the mean thickness of the retinal nerve fiber layer around the optic nerve head. The latest software versions of HRT use different analysis functions to classify a patient as normal or glaucomatous.
The HRT provides an extensive description of the optic nerve head–which can greatly contribute to the diagnosis of glaucoma and is an effective tool for following the progression of glaucoma. Analysis of the topographic maps of the retina can also be used to assess depth or elevation of the macula as well as for follow-up of various conditions, including macular edema and/or holes.
The Heidelberg Retinal Tomograph (HRT) is a proven, essential tool for detecting and managing glaucoma, especially for assisting in the identification of pre-perimetric disease and tracking progression. The Ancillary Study to the Ocular Hypertension Treatment Study (OHTS) demonstrated that optic disc analysis detected glaucoma conversion in 55% of cases, before any detectable loss of visual function. The HRT has proved to be a robust predictor of glaucoma. OHTS also concluded that the HRT recognized temporal superior defects which later developed into confirmed glaucoma in 40% of cases – looking only at baseline measurements – then confirmed the diagnosis with an average of 5 years of follow-up. Equally impressive was that 93% of all HRT cases flagged as within normal limits at baseline remained within normal limits during the same time period.
The HRT is now the gold standard for imaging the optic nerve. Eye Associates of North Bay uses the Heidelberg Retina Tomograph in its continuous effort to provide quality care to its patients.