The ora serrata separates the retina from the pars plana (Fig 2-47). Its distance from the Schwalbe line is between 5.75 mm nasally and 6.50 mm temporally. In myopia, this distance is greater; in hyperopia, it is shorter. Externally, the ora serrata lies beneath the spiral of Tillaux (see Chapter 1, Fig 1-16).
Figure 2-46 Electron micrograph demonstrating the layers of the Bruch membrane. In the upper panel, note the melanin granules in the RPE. In the lower panel, numerous infoldings of the basal surface of the RPE are evident.
(Reproduced with permission from Spalton D, Hitchings R, Hunter P. Atlas of Clinical Ophthalmology. 3rd ed. Oxford: Elsevier/Mosby; 2005:400.)
Figure 2-47 Gross photograph of the ora serrata. The pars plana and pars plicata are also shown.
(Reproduced with permission from Spalton D, Hitchings R, Hunter P. Atlas of Clinical Ophthalmology. 3rd ed. Oxford: Elsevier/Mosby; 2005:259.)
Figure 2-48 Ora serrata. Note the malformed appearance of the peripheral retina and the cystic changes at the junction between the pars plana and the retina (hematoxylin-eosin stain ×32).
(Courtesy of Thomas A. Weingeist, PhD, MD.)
At the ora serrata, the diameter of the eye is 20 mm and the circumference is 63 mm; at the equator, the diameter is 24 mm and the circumference is 75 mm. Topographically, the margin of the ora serrata is relatively smooth temporally and serrated nasally. Retinal blood vessels end in loops before reaching the ora serrata.
The ora serrata is in a watershed zone between the anterior and posterior vascular systems, which may in part explain why peripheral retinal degeneration is relatively common. The peripheral retina in the region of the ora serrata is markedly attenuated. The photoreceptors are malformed, and the overlying retina frequently appears cystic in paraffin sections (Blessig-Iwanoff cysts; Fig 2-48).
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.