IMAGING TECHNOLOGY

Imaging technologies and optical coherence tomography (OCT) in particular, have helped to improve the diagnosis and management of cystoid macular oedema (CME) in daily clinical practice, according to Gisbert Richard MD. “CME remains the most important complication we can expect to encounter after cataract surgery with an incidence of between five per cent to seven per cent in uncomplicated cases and up to 28 per cent for complicated cases such as diabetic patients without retinopathy,” he told delegates at the XXXI ESCRS Congress in Amsterdam.

Prof Richard noted that there are a lot of different parameters to be taken on board in the clinical evaluation of macular oedema, including the extent and distribution of the oedema in the macular area. “Do we have central foveal involvement, and what about fluorescein leakage? Are there intraretinal cysts, as this is a very important prognostic factor. What about signs of ischemia with broken perifoveolar capillary arcade and/or areas of capillary closure? The presence or absence of vitreous traction needs to be borne in mind, as well as any increase in retinal thickness, cysts in the retina and chronicity of the oedema,” he said. Amsler grid testing is a very good qualitative method for screening for early macular oedema, said Prof Richard. While fluorescein angiography is not needed for evaluation of the oedema it can help to provide more precise information about the focal loss of capillaries, he added.

It is OCT, however, which shines in the evaluation of macular oedema. “OCT has major advantages such as high-resolution measurements and cross-sectional images of the retina. It gives us reproducible retinal thickness measurements in normal eyes and eyes with diabetic macular oedema. The technology is noninvasive, well tolerated, fast and easy to perform. The scans are minimally influenced by media opacities, it involves a short learning curve for the clinician and it is easily understandable by patients with no medical background,” he said. Limitations of OCT include patient-related factors such as poor visual acuity and eccentric, erratic or unstable fixation, and also operator-related factors such as misidentification of artefacts or correct positioning of the callipers when manually obtaining retinal thickness measurements, said Prof Richard.

“We need to remember that OCT provides information on morphologic features but it is not capable of distinguishing the origin of macular fluid or assessing macular perfusion. Information obtained by fluorescein angiography about the source of leakage and presence of macular ischemia cannot be replaced by OCT,” Prof Richard said. The very latest generation of OCT permits much higher resolution, greater control of artefacts, option of volumetry, 3-D imaging and correlation with fluorescein angiography, he added. Information derived from the OCT scans should always be supplemented with other examinations, he concluded.