Mehmet Hakan Özdemir The Choroid and Optical Coherence Tomography

The choroid is a pigmented vascular tissue that was t histologically examined in the 17th century, and to date has been studied by various imaging methods. It extends from the ora serrata anteriorly to the optic nerve head posteriorly. According to histopathological examination, the choroid has a mean thickness of 0.15 mm anteriorly and 0.22 mm posteriorly; anatomically it forms the posterior portion of the uveal tract, which continues anteriorly with the ciliary body and the iris. From retina to sclera, the choroid comprises Bruch’s membrane, the choriocapillaris, the medium diameter choroidal vessels, and the large diameter choroidal vessels.1 A structurally and functionally healthy choroid is essential for retinal function. The central retinal artery nourishes the inner two-thirds of the choroid, whereas the choroidal vasculature nourishes the outer third. Abnormal choroidal circulation leads to retinal photoreceptor dysfunction and death.2 It has been shown that the choroid has a vital role in the pathophysiology of many diseases such as central serous retinopathy (CSR), agerelated macular degeneration (AMD), pathological myopia and Vogt-Koyanagi-Harada (VKH) disease.3,4,5,6 Thus, the clear and accurate identi ion of choroidal changes will allow the proper assessment of many posterior segment diseases. However, unlike the retina, choroidal structures are not found in distinct, ordered layers and they lack contrasting properties; therefore, for many years it was not possible to examine the choroid in as much detail as the retina.