The introduction of optical coherence tomography (OCT) into clinical practice has changed methods of the ophthalmic clinical diagnosis and treatment.With the progression of new technology, OCT has obtained a true, non-invasive optical biopsy of the posterior segment.With advancements in OCT image processing software, more refined details of the posterior segment can be analysed, such as choroid.Recently, high-definition selective imaging processing software can reduce noise and construct the best possible image by evaluating all the pixel data.And decreased signal strength posterior to the retinal pigment epithelium (RPE) is compensated by this image enhancement software, which enables visualization of the border between choroidal tissue and sclera.Thus, choroidal thickness can be accurately measured by OCT.Choroidal thickness is affected by many factors, such as body position, age, intraocular pressure, ocular axial length, refractive error, systolic blood pressure, etc.The choroid is an important part of blood supply in the eyes, which plays a vital role in the pathophysiology of many diseases affecting the retina.Choroid is significantly correlated with many ophthalmic diseases, for example, ophthalmic diseases including diabetic retinopathy (DR), myopic maculopathy, age-related macular degeneration (AMD), retinitis pigmentosa, normal tension glaucoma (NTG), high myopia, idiopathic macular hole may cause thinning of the choroid; ophthalmic diseases including central serous chorioretinopathy (CSC), polypoid choroid vasculopathy (PCV), Vogt-Koyanagi-Harada syndrome (VKH), open angle glaucoma (OAG), angle-closure glaucoma (ACG), central retinal vein occlusion (CRVO), multiple evanescent white dot syndrome may cause thickening of choroid.This article reviews the characteristics of choroid thickness, the influencing factors of choroidal thickness and the changes of choroid thickness in ophthalmic diseases.

Choroidal thickness; Tomography, optical coherence; Influencing factors; Ophthalmic diseases