Change or trend analysis is another tool to apply in the management of patients with ocular conditions that may affect the optic nerve, the retinal nerve fiber layer and the ganglion cell complex. It must be remembered that this is not the absolute tool for the decision making process but rather another tool in the management armamentarium.
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The power of spectral domain OCT (DIGITAL IMAGING) is incredibly impressive. Spectral Domain Optical Coherence Technology (SDOCT) has redefined the diagnosis and management of ocular disorders. However, the clinician interpreting the data must understand that anatomical characteristics can confound the resulting scans allowing for potential misinterpretation. Disc size and morphology is critical in the consideration of anatomical variations and how they impact on results and interpretation.
The Power of Focal Loss Volume (FLV%) and Global Loss Volume (GLV%) in the Diagnosis and Management of Glaucoma as Measured by Visual Field Progression
The analysis of the Ganglion Cell Complex is a measure of thinning of the inner retinal layers…the neurological representation of the retina. There are a number of ways to assess the Ganglion Cell Complex (GCC) thickness metric available on SD-OCT devices. Overall average thickness may be depressed in a number of conditions including normal tension glaucoma, primary open angle glaucoma, retinal arterial occlusive disease, type 1 diabetic retinopathy, sleep apnea, and the dementias. There may be isolated pockets of thinning in the GCC in other conditions such as normal tension glaucoma and ischemic optic neuropathy. Asymmetry, which is critical to all differential diagnosis, is highlighted by most SDOCT instruments.
More attention is now being directed at other quantifiable aspects of this Ganglion Cell Complex feature including the metrics focal loss volume percentage and global loss volume percentage. The only devices currently approved to calculate Focal Loss Volume Percentage (FLV%) and Global Loss Volume Percentage (GLV%) are those manufactured by Optovue, Inc Fremont CA. The FLV% and GLV% concept is illustrated in the following graphic. FLV% demonstrates “the potholes in the topography of the Ganglion Cell Complex” and GLV% shows an “overall thinning of the topography of the Ganglion Cell Complex.” Both the FLV% and GLV% are now revealing potential in assistance in differential diagnosis and management of ocular disease.
AN INTRODUCTION TO A NOVEL TECHNOLOGY
The vitreoretinal interface (VRI) contains a diverse mix of extracellular molecules, including collagen, laminin, and fibronectin, that facilitate the adhesion between the vitreous cortex and the innermost retinal layer (the internal limiting membrane—ILM).
Recent imaging advances in optical coherence tomography (spectral domain; SD-OCT) have advanced the accuracy with which diseases of the VRI are diagnosed and managed. Even though patients may be totally asymptomatic, issues such as vitreomacular adhesion and vitreomacular traction may be present. While many do not warrant consultation for possible intervention, the primary-care practitioner will nonetheless uncover the “sleeping condition” with spectral domain optical coherence tomography (SD-OCT) and will need to make decisions.