Correlation Between Choroidal Thickness and Myopia Using Swept Source OCT

It has evolved over the past decade as one of the most important ancillary tests in ophthalmic practice. It is a noninvasive imaging technique and provides high resolution, cross-sectional images of the retina, the retinal nerve fiber layer and the optic nerve head. With axial resolution in the 5-7 μm range, it provides close to an in-vivo 'optical biopsy' of the retina. Optical coherence tomography employs light from a broadband light source, which is divided into a reference and a sample beam, to obtain a reflectivity versus depth profile of the retina. The light waves that are back scattered from the retina, interfere with the reference beam, and this interference pattern is used to measure the light echoes versus the depth profile of the tissue in vivo. Recently, a new type of optical coherence tomography instrument, called a swept source optical coherence tomography, was introduced. The Swept source optical coherence tomography uses a tunable laser (swept-source) as a light source with a longer wavelength that allows the light to penetrate deeper into tissues than the conventional spectral domain optical coherence tomography instruments. This, then, enabled the imaging of the choroid. Because choroidal abnormalities such as vascular hyperpermeability, vascular changes, loss and thinning are critical to the onset and progression of many ocular diseases, ophthalmologists and researchers are shifting their interest to the choroidal abnormalities. Being a major vascular layer of the eye , choroid plays an important role in ocular health, and is involved in the pathogenesis of many intraocular diseases such as age-related macular degeneration , polypoidal choroidal vasculopathy , central serous chorioretinopathy and myopic macular degeneration. Accurate measurement of choroidal thickness in vivo is an essential step in monitoring disease onset and progression that lead to choroidal thinning. Based on histologic study, choroidal thickness ranges from 170 to 220 um. These disorders show the need for understanding the choroidal structure in ocular diseases and the importance of having database of choroidal thickness.