Updates On Optic Disc And Nerve Fiber Layer Imaging In Glaucoma

Abstract

Glaucoma is a slowly progressive optic neuropathy results from accelerated loss of retinal ganglion cells (RGCs) and their axons, leading to retinal nerve fiber layer (RNFL) attenuation and optic neuropathy. Glaucomatous damage is characterized by specific pattern of damage to the optic nerve head (ONH) and visual field loss Therefore, identification of early glaucomatous changes not only can help clinicians in confirming the initial diagnosis but also, more importantly, can alert them that further treatment may be required to prevent visual impairment due to glaucoma. Although optic disk stereophotography represents the standard for documentation of glaucomatous structural damage in practice and research trials, advances in computerized imaging technology provide useful measures that assist the clinician in glaucoma diagnosis and monitoring and offer considerable opportunity for use as efficacy endpoints in clinical trials, the imaging technologies are powerful tools that may assist the clinician in the early diagnosis of glaucoma. They provide more objective documentation and precision for diagnosis and progression detection. Furthermore, these technologies facilitate earlier detection of functional loss and enhance assessment of structure-function correspondence. Glaucoma progresses slowly and it is important to detect real change due to disease that is beyond normal age loss and short-term and long-term fluctuations. Advanced ophthalmic imaging devices provide objective quantitative measures of neuroretinal rim, RNFL thickness and ONH to¬pography with high repeatability and low variability. One of the challeng¬ing aspects of ocular imaging is improving signal-to-noise ratio, and detecting real structural change due to disease that is beyond the normal variability. Different imaging technologies use different algorithms for this purpose. Several reports have indicated that these technologies are capable of identifying glaucomatous damage at an early stage. Imaging instruments offer the advantage of providing large amount of reproducible data that can be used to develop analysis strategies for detecting change over time. Each instrument is in a different stage of development with important software improvements anticipated, particularly for detecting change overtime. Several imaging technologies have included progression analysis packages that compile several visit dates into trend based analysis designed to assist the clinician in monitoring glaucoma progression. It is essential the clinicians understand the strengths and limitations of each instrument and interpret the data accordingly. Moreover, it is important to use good quality images in conjunction with a complete clinical examination and assessment of visual function for patient management decisions. Therefore, the clinician who successfully integrates imaging in practice complements their clinical evaluation with adjunctive diagnostic testing.