Retinal Thickness

The HRT provides retinal thickness measurements with absolute millimeter measurement.  Unlike the Edema Index, the Retinal Thickness function locates both the vitreo-retinal interface and the retinal pigmented epithelium (RPE). 

A beam of light scans the retina and two major signal peaks are detected.  The largest signal peak corresponds to the internal limiting membrane (ILM) and the second largest signal peak corresponds to the RPE.  The HRT then calculates the difference between the two peaks to arrive at the millimeter difference. 

The HRT scans a 15-degree area using 384 x 384 pixels or nearly 150,000 measured points across the measurement area.  Other technologies use cross-sectional imaging which only “samples” the area and interpolates the values between scan lines.  HRT data is not interpolated.