Tomographic reconstruction of the retina using a confocal scanning laser ophthalmoscope

Modern technologies for retinal scanning and imaging: an introduction for the biomedical engineer

This review article is meant to help biomedical engineers and nonphysical scientists better understand the principles of, and the main trends in modern scanning and imaging modalities used in ophthalmology. It is intended to ease the communication between physicists, medical doctors and engineers, and hopefully encourage “classical” biomedical engineers to generate new ideas and to initiate projects in an area which has traditionally been dominated by optical physics. Most of the methods involved are applicable to other areas of biomedical optics and optoelectronics, such as microscopic imaging, spectroscopy, spectral imaging, opto-acoustic tomography, fluorescence imaging etc., all of which are with potential biomedical application. Although all described methods are novel and important, the emphasis of this review has been placed on three technologies introduced in the 1990’s and still undergoing vigorous development: Confocal Scanning Laser Ophthalmoscopy, Optical Coherence Tomography, and polarization-sensitive retinal scanning.

Exploring retinal and functional markers of diabetic neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most debilitating complications of diabetes. DPN is a major cause of foot ulceration and lower limb amputation. Early diagnosis and management are key factors in reducing morbidity and mortality. Current techniques for clinical assessment of DPN are relatively insensitive for detecting early disease or involve invasive procedures such as skin biopsies. There is a need for less painful, non-invasive, safe evaluation methods. Eye-care professionals already play an important role in the management of diabetic retinopathy but recent studies have indicated that the eye may also be an important site for the diagnosis and monitoring of neuropathy. Corneal nerve morphology is a promising marker of diabetic neuropathy occurring elsewhere in the body. Emerging evidence tentatively suggests that retinal anatomical markers and a range of functional visual indicators could similarly provide useful information regarding neural damage in diabetes, although this line of research is less well established. This review outlines the growing body of evidence supporting a potential diagnostic role for retinal structure and visual functional markers in the diagnosis and monitoring of peripheral neuropathy in diabetes.

Surface reconstruction from retinal laser images

The aim of This work is to describe techniques that lead to surface extraction of the retinal structure. Based on the tomographic data from the confocal scanning laser ophthalmoscope (CSLO) we perform some necessary preprocessing steps to correct the nonuniform illumination and to suppress the noise. Then we extract the surface and perform some postprocessing operations before visualization. First results of ongoing research are presented and also the suggestions for future research are proposed.

A reference standard for the measurement of macular oedema

Macular oedema is associated with several conditions that lead to blindness. Accurate measurement of macular thickness is important in order to follow disease progression and evaluate treatments. Four techniques are examined to determine the best reference standard for the detection and quantification of macular oedema: ultrasound, optical coherence tomography, the retinal thickness analyser, and the scanning laser ophthalmoscope. The three optical techniques have the highest resolution and sensitivity, in particular optical coherence tomography. Ultrasound can be useful where dense opacities preclude optical imaging.

The scanning laser ophthalmoscope--a review of its role in bioscience and medicine

The scanning laser ophthalmoscope (SLO) offers the potential for retinal imaging that is complementary both to that of the fundus camera and also the newly developing technique of optical coherence tomography (OCT). It has the ability to produce rapid images at low light levels using light of specific wavelengths. This permits temporal studies of fluorescent-labelled cells which offer a unique insight into inflammatory processes in the eye. The facility to image with several different wavelengths simultaneously offers the potential for spectral imaging of retinal tissue with the aim of revealing those early changes in tissue perfusion that indicate the onset of retinal disease, so increasing the probability of successful therapy.

Characterization of leakage activity in exudative chorioretinal disease with three-dimensional confocal angiography

PURPOSE

A novel angiographic technique providing topographic imaging of chorioretinal fluorescence is applied to the characterization of leakage dynamics in exudative chorioretinopathy. The three-dimensional imaging is evaluated with respect to results with conventional two-dimensional fluorescence angiography.

DESIGN

Prospective observational case series.

PARTICIPANTS

Thirty eyes of 30 patients with different exudative maculopathies (pigment epithelium detachment, branch retinal vein occlusion, central serous chorioretinopathy, each n = 10) and 11 eyes of 10 patients with clinically normal appearance.

METHODS

Depth-resolved fluorescence angiography using a confocal scanning laser system was performed after complete ophthalmologic examination. The axial distribution of fluorescein and indocyanine green fluorescence at each x/y position within a tomographic scan of 32 images was analyzed. The chorioretinal fluorescence topography was reconstructed by localizing a defined threshold value of fluorescence and displayed as topographic relief. Qualitative description and quantitative measurements of exudation or structural alterations were performed topographically and conventionally.

MAIN OUTCOME MEASURES

Qualitative and quantitative analysis of structural or exudative changes in time course in topographic illustration compared with conventional angiography.

RESULTS

Clinically physiologic eyes were presented topographically as a smooth concave surface of fluorescence with defined illustration of retinal vascular structures and the optic disc. Retinal vascular pathologic conditions induce a precisely demarcated pattern of intraretinal edema with a characteristic temporal evolution. In central serous retinopathy the underlying pathologic condition was identified as a perfusion defect, which was subsequently filled with a peak of exudation with differences in the time of maximum in fluorescein/indocyanine green angiography. Pigment epithelium detachment appeared as a high and well defined elevation, with the origin of exudation within the base of the detachment. Differences in the time of maximum prominence were found in indocyanine green angiography within the pigment epithelium detachment group.

CONCLUSIONS

Confocal topographic angiography allows for the first time precise three-dimensional functional imaging of fundus alterations caused by leakage or barrier dysfunction. Compared with conventional angiography, depth-resolved angiographic imaging is less impaired by masking phenomena or low fluorescence intensity, which improves the diagnostic yield of angiography. The characterization and quantification of leakage activity is a promising tool in the assessment of exudative maculopathy.

True colour imaging of the fundus using a scanning laser ophthalmoscope

Currently retinal imaging is performed with the fundus camera. This has a number of limitations, in particular the high level of illuminations required for imaging. The scanning laser ophthalmoscope (SLO) has been proposed as an alternative imaging device but to date one of its main limitations has been that it gives only monochromatic images. In this paper we describe an SLO which uses low power red, green and blue lasers to image the human fundus. Using three lasers simultaneously to produce a colour image will increase the fundus exposure by a factor of three. To overcome this problem, a technique has been developed for multiplexing the lasers so that each point on the retina is imaged by the three lasers pulsed rapidly in sequence. The total exposure is thus kept to the same level as for a single laser and total imaging time is not increased. An example is shown of the image from a patient with diabetic retinopathy.