Thirty-three patients with type 2 IMT underwent complete ophthalmic examination, including slit lamp examination with indirect ophthalmoscopy, fluorescein angiography by confocal scanning laser ophthalmoscopy (cSLO; HRA2; Heidelberg Engineering, Heidelberg, Germany), fundus photography (FF450; Zeiss, Jena, Germany), and OCT imaging (Stratus OCT; Carl Zeiss Meditec, Jena, Germany).
CBR images at a wavelength of 488 nm (argon laser) were obtained using the HRA2. The confocal pinhole of our system had a diameter of 100 μm and a depth of focus (full width at half maximum) of 4.1 diopters (D), resulting in a drop of the detected reflectance signal of about twofold at approximately 2-D defocus. The appearance of a normal fundus in CBR imaging is shown in
Figure 1A . In eight patients, additional stereo images were obtained by rotating the camera without making any vertical adjustment or movement of the fixation device. Stereo images were viewed using a stereoscopic viewer (Stereo-Vu; PS Manufacturing, Portland, OR) that allows fusion of the two images into one stereoscopic image.
Macular pigment optical density (MPOD) was assessed using a modified confocal HRA classic (Heidelberg Engineering), as described.
20 21 Briefly, the instrument uses two argon excitation wavelengths at Λ
1 = 488 nm and Λ
2 = 514 nm, in conjunction with a barrier filter that blocks all wavelengths shorter than 560 nm. The system software generates an averaged autofluorescence image from two movies (each consisting of 16 images) acquired with each of the two excitation wavelengths. Macular pigment absorbs light in the short wavelength range, with a maximum at 460 nm. Therefore, the autofluorescence image at 488 nm shows a strong dependence on macular pigment density because the excitation wavelength at 488 nm is absorbed considerably more than at 514 nm. This results in reduced autofluorescence at 488 nm with increasing macular pigment density. Subtraction of the two averaged images results in an image representing the MPOD. A normal macular pigment distribution is shown in
Figure 1B .
Images were analyzed using image analysis software (Heidelberg Eye Explorer [HEE]; Heidelberg Engineering). Using anatomic landmarks such as retinal blood vessels, the software allows outlining a region of interest manually and overlying the outline with a second image of the same eye. The region of interest is defined by a white line in the respective figures, enabling comparison of the size of the area of interest.
The study adhered to the tenets of the Declaration of Helsinki, and it was approved by the local ethics committee of the University of Bonn. Informed consent was obtained from all patients.