Dr. Prashant Srivastava is an experienced and one of the most trusted glaucoma specialist in Kolkata. He has done more than Ten Thousand glaucoma surgeries during his illustrious career. This section will tell us more about glaucoma from the glaucoma surgeon himself.
Glaucoma is a leading cause of blindness and vision-related morbidity. It is estimated that over Fifty Eight million people will have open-angle glaucoma by the year 2020, with Ten per Cent bilaterally blind. In 2010, it was estimated that there are approximately 11.2 million persons aged forty years and older with glaucoma in India. Since the disease is silent and irreversible, it essential to diagnosed the disease at the earliest so that the risk of visual impairment and related morbidity can be minimized.
The diagnosis of glaucoma
Both functional and structural tests are needed to diagnose the disease but few studies have demonstrated that there may be disagreement between structural and functional tests. Though in most of the patients structural changes precedes functional loss, in few patient functional loss is more marked than structural changes.
Standard automated perimetry
The assessment of visual function with standard automated perimetry is the gold standard of glaucoma diagnosis and monitoring Glaucoma may first be detected due to a visual field abnormality. Due to the logarithmic scale, significant neural losses are likely to correspond to relatively small changes in SAP sensitivity at early stages of disease compared to relatively large changes in later disease.
Therefore the ability to diagnose the early disease is less as compared to advanced disease. To overcome this difficulty other functional tests like frequency-doubling technology (FDT), short-wavelength automated perimetry (SWAP), and flicker-defined form (FDF) perimetry have been developed. These tests aim to target specific aspects of visual function, such as movement perception, contrast sensitivity, and colour vision.
SWAP uses a narrow-band blue-light stimulus and yellow-background illumination to emphasize the response characteristics of the blue–yellow pathway. Medeiros et al examined the effect of disease severity on the diagnostic performance of matrix FDT perimetry and SAP and found FDT may have better accuracy in early disease.
Structural changes can be by clinical examination and optic disc stereophotographs. Patients with progressive optic disc changes were found to be almost Twenty Six times more likely to develop a visual field defect compared to those in whom no change in disk appearance was detected. However, to the large variations in normal disc appearance and their subjective interpretation diagnosis sometimes becomes difficult .To overcome this new methods to assess structural changes like optical coherence tomography (OCT), scanning laser polarimetry, and confocal scanning laser ophthalmoscopy (CSLO) have been developed . These tests provide objective and quantitative measurements of such parameters as RNFL thickness or neuroretinal rim area. They also include normative databases that allow eyes to be categorized as normal, borderline, or outside normal limits.
Spectral domain OCT has much better reliability and repeatability due to reduced scan-acquisition times, greatly enhanced resolution, and improved layer segmentation. Newer studies are showing that SDOCT RNFL loss over time can also be used to predict the risk of future development of visual field loss in eyes with suspected glaucoma.
Leung et al found RNFL measurements obtained using SDOCT had excellent ability to detect glaucoma, with global RNFL thickness having a sensitivity of Ninety One point Six per Cent for a specificity of Eighty Seven point Six per Cent and an AUC of Zero point Ninety Six point Eight (0.96.8)
Combining structural and functional tests
The combination of structural and functional measures will provide better diagnostic ability than any isolated test. Therefore for detection of early glaucoma, new strategies are being developed to combine
data from structure and functional changes. Future software may allow incorporation of risk factors and clinical examination findings into these calculations. Including information regarding risk factors, such as intraocular pressure, central corneal thickness, and the presence or absence of disc haemorrhages, is likely to improve diagnostic accuracy and may allow early disease detection.
The underlying pathological feature of glaucomatous optic neuropathy is loss of RG Cs1; therefore, were it possible to directly measure RGC loss, this might offer the best method to detect early glaucomatous damage. Although direct quantification of RGCs is not yet possible in vivo, Harwerth et al have described empirical formulas that allow RGC counts to be estimated from perimetric threshold-sensitivity values.
The ability to estimate RGC counts from OCT and SAP for the first time provides a common and intuitive measure for expressing the results of structural and functional tests. This has the potential to improve our understanding of the relationship between structural and functional tests in glaucoma, with important implications for early detection of disease.
As the quality of life may get affected with even mild loss of the visual field, therefore we need to correlate both structural and functional tests to beat the glaucoma early so that our patients can enjoy life long vision.
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