The Ophthalmology Service of Créteil utilizes a technical platform incorporating numerous types of exams for clinical investigation. These techniques encompass retinal imaging and functional analysis including fluorescein angiography, Green Infracyanine angiography, optical coherence tomography (OCT), ocular ultrasound, visual field mapping and electrophysiology.
Fluorescein angiography is a critical exam used to diagnose retinal pathology and in particular Age-related Macular Degeneration. Fluorescein, a vital dye, is injected into the antecubital vein. The dye emits a fluorescent light when stimulated by light of a particular wavelength. Angiography is performed by imaging the retina while the dye is circulating in the retinal vessels.
Infracyanine Green Angiography
Infracyanine Green Angiography ICG utilizes a different dye, indocyanine or infracyanine green. ICG complements fluorescein angiography and allows exploration of the choroid, the vascular tissue beneath the retina. ICG is used in wet AMD as the technique permits the visualization of occult vessels, located under the retina. ICG is also utilized to diagnose the etiology of retinal inflammation.
Optical Coherence Tomography
OCT is an imaging modality that is rapid, painless and non-invasive in as much as it does not require an injection. OCT provides information that complements angiography.
In this technique, a beam of light using a laser source is beamed through the structures of the eye and a camera measures the time taken by the light echo to cross the ocular tissues, and be reflected back. It allows detailed analysis of the structures comprising the full thickness of the retina.
Ocular ultrasonography uses ultrasound to explore the intra-ocular structures whenever visualization of the fundus is impossible. This may be due to a cataract or vitreous hemorrhage which prevents accurate observation of the retina. Ultrasound is also used to select an appropriate implant to replace a lens prior to cataract surgery.
Two modes of ultrasound are used in ophthalmology.
- Mode «A» (amplitude mode) is the oldest. It consists of interpretation of the inflection of a line relative to a baseline. Every structure in the eye induces a peak or series of peaks corresponding to the «echo» of the structure.
- Mode «B» (brightness mode) is currently the most utilized mode. The ultrasound is not linear but rather is a two-dimensional section of the globe, permitting a more detailed analysis.
Visual Field Exam
The visual field exam is utilized in a number of pathologies. In Chronic glaucoma , this exam is especially important. Two types of visual field testing are performed: manual Goldmann perimetry and automated perimetry.
Electroretinography (or ERG) consists of a measurement of the electrical activity of retinal cells while the cells are stimulated with a light source. The trace obtained during the measurement records the responses of of cones and rods, the photoreceptors (visual cells) of the eye. This complementary exam is particularly important in the diagnosis of genetic diseases and retinal degeneration.