Heidelberg Engineering Technologies
A new era in imaging structures of the eye was born in 1991 with the introduction of a series of hybrid instruments from Heidelberg Engineering. Heidelberg Engineering combines medicine and physics to image the finest details of the eye; details thinner than a sheet of paper and smaller than a pinhead.
Precise measurement of these tiny eye structures has enabled clinicians to detect changes to the eye years in advance of recognizable disease. New anatomical structures are being discovered using our technologies and hopes have been raised for applying and understanding the role of new therapies to such devastating diseases such as age-related macular degeneration and diabetic retinopathy.
Years of development and long term clinical studies have proved the value of the company’s technology in recognizing and measuring eye disease. Below is a description of the technologies in the company’s product portfolio.
I. Tracking Laser Tomography
Heidelberg Engineering is the first company to introduce tracking laser tomography, a technology which enables aquiring real-time, simultaneous images while tracking eye movement. Utilizing our TruTrack™ image alignment software, instruments are designed to continuously monitor the position of the eye using a beam of light. With the Spectralis®, once eye tracking is engaged, the instrument tracks the motion of the eye and directs a second beam of light to its correct position, much like a missile tracking system.
This innovative technology combines the first dual-beam scanning instrument with simultaneous confocal SLO and spectral-domain OCT imaging. It uses the best high resolution cross-sectional images of the eye in conjunction with the best high resolution images of the retinal surface, providing precise location information and multiple imaging modalities on a single platform.
Not only can the technology record the precise location of pathology, it enables the Heidelberg Noise Reduction™ software to produce higher quality images, and it enables the Auto Rescan function to track change over time. Tracking change between office visits is critical to knowing if disease is progressing or if therapy is having the desired effect. Heidelberg Engineering offers the only instrument which can track locations on follow-up examinations without requiring the operator to find the scan location.
The ability to have eye tracking, retina recognition, and automatic rescan of the same location are key characteristics of this new hybrid technology known as tracking laser tomography.
II. Confocal Scanning Laser Tomography
Heidelberg Engineering’s technology base began with confocal scanning laser tomography. This technology uses laser light to illuminate tissue and capture high resolution images of the retina at high speed. Speed is important because the human eye is in constant motion. Even when a person concentrates on a fixed point, the eye is constantly making tiny involuntary movements, called saccades, in anticipation of locking onto a new point.
Because a laser image of the retina can be captured in 24 milliseconds, most motion artifact is eliminated using the same principle as stop-action photography. Prior to the development of laser imaging, such stop-action photographs could only be done with a camera and a high intensity flash. Laser imaging uses 1/100th of the amount of light of a camera flash to capture a map of the retina and retinal blood vessels. Using our proprietary TruTrack™ image alignment software, images can be precisely aligned and measured in 3-D.
II.a. Confocal Imaging
Confocal imaging is the process of shining light on an object, then capturing reflected light by passing the light through a pinhole. The pinhole blocks light not coming from the focal plane or layer of interest, and blocks scattered light which can “fog” the image. The result is focused, high resolution images without glare.
II. b. Tomography
Confocal imaging also enables high resolution images to be captured at varying depths in tissue by producing an optical slice or section. This technology is known as tomography. The Heidelberg Retina Tomograph (HRT) and Heidelberg Retina Angiograph (HRA) are designed to capture tomographic slices of the inside of the retina. The HRT uses the tomographic information to construct a topographic map of the surface of the eye to detect and measure changes due to diseases such as glaucoma. The instrument also uses tomographic slices through the retina to recognize edema and to recognize key retinal layers, such as the internal limiting membrane (ILM) and the retinal pigmented epithelium (RPE), for measuring retinal thickness.
Images captured by confocal scanning laser ophthalmoscopes are transverse images, (captured in the x and y axis), while looking “down” at the retinal surface. If one imagines the retina as a ream of paper, transverse tomographic images are similar to each of the sheets of paper in the stack. Each sheet of paper or tomogram, has a high resolution image of the blood vessel pattern of the eye. Because of this, it is possible to stack and align the image slices to create a three-dimensional model of the eye.
II. c. Advantages of Confocal SLO
The advantages of confocal scanning lasers are speed and location. Lasers can scan rapidly in the x-y axis, avoiding eye movement artifact. In addition, the images contain detailed mapping of the retinal structures (such as blood vessels) making it easy to compare it to the view a clinician sees through a standard ophthalmoscope. This helps enables identification of the exact location of the pathology and ensures a repeat scan in the same location at a subsequent exam.
III. Optical Coherence Tomography
Optical coherence tomography (OCT) is another way of looking at the eye using a laser-like light source known as a super luminescent diode (SLD). Compared to lasers which produce a single peak wavelength, an SLD produces a wider band of wavelengths around a peak, enabling information to be gathered simultaneously at multiple wavelengths.
The multiple wavelengths allow the rapid collection of data in the tissue depth (z-axis), which results in detailed cross-sectional images of the retina.
III. a. Time-Domain OCT
Using OCT, a beam of light is projected and split into two beams. One beam is sent into the tissue and one beam is sent to a moving reference mirror. The beam sent to the tissue is compared to the beam sent to the reference mirror and this enables exact measurement of the distance to the tissue. High resolution, cross-sectional images of the retina can be obtained; however, the transverse (x-y) scanning speed is slower, so the images are subject to motion artifact.
When applied to tissue, OCT allows a large amount of information to be collected in the depth direction (z-axis) enabling high resolution, cross-sectional images. If we picture the retina as a ream of paper, the OCT acts like an invisible paper cutter, slicing down through the stack of paper, creating a cross-sectional image of the layers of the paper.
This method of imaging has the advantage of providing detailed information on the layers of the retina, while having limited information the transverse direction. The technology has also been applied to the cornea for cross-sectional images of the front of the eye, known as the anterior chamber.
III. b. Spectral-Domain OCT
Spectral-domain OCT, also known as Fourier-domain OCT, is a significant improvement on time-domain OCT. Spectral-domain OCT eliminates the moving reference mirror found in time-domain, enabling scan rates up to 100 times faster. With spectral-domain OCT, all of the wavelengths of returning light are analyzed simultaneously, resulting in faster collection of more data. Faster scan rates are desirable to help limit motion artifact and to obtain more information in order to locate the position of the scan in the eye.
Heidelberg Engineering selected a long wavelength superluminescent diode (SLD) with a peak wavelength of 870 nm to enable the best penetration of infrared light through cloudy media, often found in aging patients due to cataracts and other signs of aging.
IV. TruTrack™ Image Alignment
TruTrack™ is the name of our proprietary software algorithm which recognizes and uses the retina and other eye structures to align images. It was first used in the HRT to align tomographic scans of the retina for reconstructing three-dimensional images of the optic nerve head. As the benefits of HRT in glaucoma developed, the software was applied to retinal imaging on the HRA platform and later to edema and thickness measurements on the HRT Retina Module.
The software uses sophisticated image recognition algorithms to identify key structures of the eye including blood vessels and image variations. Over 500 data points are identified and compared in order to match and align images.
With the introduction of the Spectralis® tracking laser tomograph, TruTrack™ technology enables real time eye tracking, Heidelberg Noise Reduction™ and Auto Rescan functions. The combination of our TruTrack™ image alignment software with confocal SLO and spectral-domain OCT is enabling a new level of detailed images and precision measurements which were not previously available.
V. Heidelberg Noise Reduction™
Heidelberg Noise Reduction™ uses our TruTrack™ software to produce high quality images. Applying our eye tracking technology, multiple images are obtained from the same location. These images are compared and combined, filtering random noise (sometimes called “speckle”) from the final image. This is similar in concept to the way that Dolby® Noise Reduction produces high fidelity sound in recordings.