Myopic arcs are the most common fundus change in myopic eyes. The smallest are not easily visible, and the largest can reach the size of the optic disc. Some surround the optic disc, or even reach the macula. If the myopic arc does not invade the macula, it will have little effect on vision; if it does, vision (including near vision) will be significantly reduced. When diagnosing whether a patient has myopic arc, care should be taken to distinguish between myopic arc and ocular toxoplasmosis and age-related macular degeneration. Ocular toxoplasmosis Highly myopic macular degeneration is not difficult to diagnose based on its history of highly myopic eyes with typical leopard-like fundus and typical degenerative changes of the optic disc myopic arc and macula. However, sometimes it should be distinguished from ocular toxoplasmosis, especially the resting stage or congenital. Although ocular toxoplasmosis is a form of uveitis, there is often no anterior inflammation and only lesions of the posterior uvea, which are also located in the posterior pole. In the resting phase or congenital form, it may only present as old atrophic circular lesions in the macula, which may be surrounded by hyperpigmentation, similar to the atrophic lesions of high myopia. However, patients with toxoplasmosis have a history of exposure to animals such as cats and dogs, and additional skin tests and serological tests are available to demonstrate this. Finally, diagnostic treatment is also available. Ocular toxoplasmosis can be significantly treated with sulfonamide, minocycline, and clindamycin in combination with hormonal therapy. Age-related macular degeneration In the elderly, highly myopic macular lesions manifesting as organic scarring with choroidal neovascularization are to be differentiated from age-related macular degeneration. Generally the choroidal neovascular membrane is smaller and subcentral in the former, while the latter is often associated with fundus arteriosclerosis or hypertensive changes. And in addition to disc scarring, there may be changes of early age-related disc lesions, such as single or fused vitreous warts, pigment epithelial plasmacytosis or hemorrhagic detachment, and other changes. Through the observation of the myopic arc of the optic disc, it is possible to distinguish whether the myopic eye is axial or refractive myopia, and to make a preliminary judgment and evaluation of the refractive index of axial myopia, which has its clinical significance as a means of examination before astigmatism and can be considered an objective and simple examination method. Recently, some people have used fundus stereophotography and computer image processing to study the changes in the myopic arc and concluded that the width of the myopic arc is significantly correlated with the degree of myopia. Thus, further study of the changes in the myopic arc with new techniques may be useful in evaluating whether myopia is developing and in differential diagnosis.