HEIDELBERG HRA 2, Operation Manual

Page: 7 / 50

3
1 Introduction
1.1 Intended use
The Heidelberg Retina Angiograph 2 is a diagnostic device for the human eye.
Intended use is for the examination of the retina by laser scanning either with or without contrast
agent, resp. fluorescence agent). The purpose of the angiography testing is to assist in the diagno-
sis of eye diseases. The diagnostic result shall provide help to the physician for adequate therapy.
1.2 The Heidelberg Retina Angiograph 2
The Heidelberg Retina Angiograph 2 is a confocal laser scanning system for digital fluorescein
and indocyanine green angiography. Fluorescein and indocyanine green angiography can be per-
formed either separately or simultaneously.
For acquisition of the digital confocal images, a laser beam with a wavelength suitable to excite
the fluorescent dye is focused on the retina. The laser
beam is deflected periodically by means of oscillating
mirrors to sequentially scan a two-dimensional sec-
tion of the retina. The intensity of the emitted fluo-
rescent light at each point is measured with a light
sensitive detector. In a confocal optical system, light
emitted outside of the adjusted focal plane is sup-
pressed. This suppression increases with the distance
from the focal plane, and results in a high contrast
image. Furthermore (especially during indocyanine
green angiography), the confocal optical system al-
lows the user to acquire three-dimensional images
layer by layer, which is comparable to laser scanning
tomography.
The laser sources contained in the Heidelberg Retina
Angiograph 2 emit laser light of three different wave-
lengths: for fluorescein angiography, the blue line of
a solid state laser (488 nm) is used to excite the fluo-
rescein. A barrier filter at 500 nm edge wavelength
separates excitation and fluorescent light. The same
wavelength (but without barrier filter) is used to create red free reflectance images. For indocya-
nine green angiography, a diode laser at 795 nm wavelength is used to excite the dye, while a bar-
rier filter at 810 nm edge wavelength separates excitation and fluorescent light. A second diode
laser at 830 nm wavelength serves to produce infrared reflectance images.
Several image acquisition modes are provided, i.e. pure fluorescein angiography, pure indocya-
nine green angiography, and simultaneous fluorescein / indocyanine green angiography. In the
simultaneous mode, each image line is scanned twice. During the first scan, fluorescein is excited
and its fluorescence is measured; during the subsequent second scan, indocyanine green is excited
and its fluorescence is measured. In every acquisition mode, individual images, time resolved im-
age sequences, or a focal series of images (layered, three-dimensional images) can be acquired.
The images are immediately digitized with a resolution between 384 x 384 and 1536 x 1536 pix-
els. The digitized images are stored in the computer's main memory and then saved on the com-
puter's hard disk. The size of the field of view can be set to 15 x 15 degrees, 20 x 20 degrees, or
30 x 30 degrees.