View visitor information during the COVID-19 pandemic »

Hospital  >  Departments  >  Ophthalmology & Vision Sciences  >  Welcome to Ophthalmology & Vision Sciences

Patient Education: Diseases Conditions Treatments & Procedures

Heidelberg Retinal Tomograph (HRT)


HRT is the commonly used term for a machine called the Heidelberg Retinal Tomograph. This is a powerful digital imaging system that is used to analyze the optic nerve as a part of glaucoma care. The HRT uses reflection of light from the back of the eye to image the structures of the back of the eye 32 times in a couple of seconds. It then builds up a picture of the surface topography essentially producing a 3-D picture. In glaucoma care, the image is centred on the optic nerve. The optic nerve is part of the eye that is damaged by glaucoma.

The image produced provides a record of the appearance of the optic nerve at the time of the test. However, there are significant advantages to the HRT system over a diagram made by the doctor, or even a regular photograph of the optic nerve. The first is that the image is compared to a database of normal eyes, and the software whether the measurements are within the normal range or not. The other, the more important, analysis that is provided by the machine is a progression analysis. The HRT will evaluate all subsequent images and compare them to the first. If there is a change, the analysis program will show red pixels when the change is worse and green pixels if the change is for the better. These changes may be more subtle than the ophthalmologist's eye can pick up in the early stages and provide early warning that the glaucoma is progressing.

If my HRT is abnormal does that mean I have glaucoma?

No. There is a very wide range of normal in the appearance of the optic nerve. Many people fall outside the range that the software considers normal, but do not have glaucoma. They are considered at higher risk than normal, and repeat evaluations may be recommended more frequently than for people with a normal image, but they do not have the disease. The true diagnosis of glaucoma is made when there is progression or change of the abnormality.