Issue link: http://retinalphysician.epubxp.com/i/783300
39 R E T I N A L P H Y S I C I A N | N O V E M B E R / D E C E M B E R 2 0 1 6 39 R E T I N A L P H Y S I C I A N . C O M | J A N U A R Y / F E B R U A R Y 2 0 1 7 entire shape of the eye (Figure 4). e 3D MRI technique is well suited to examine the eye shape over a wide area that can encompass even a large posterior staphyloma from any angle. e author used 3D MRI and reported posterior out- pouching of the globe, suggesting staphyloma was observed in 50.5% of the eyes with mean axial length of 30.0 mm. 4 More recently, the author used a combination of 3D MRI and Optos in Japanese and Spanish patients and reported a similar prevalence (55% of the eyes with mean axial length of 30.5 mm). 9 ese data also showed that even among very long eyes (axial length of 30 mm) about a half of them do not have posterior staphylomas; they were simply elongated in an anteroposterior direction. 9 e most predominant type was wide macular staphy- loma (74% of eyes with staphyloma), followed by narrow macular staphyloma (15% of eyes with staphyloma). WIDEFIELDS: FUNDUS IMAGING AND OCT Despite the usefulness of 3D MRI, it is still difficult to per- form in a large population of patients in routine clinical settings. It also remains difficult to perform 3D MRI due to availability and cost. As a surrogate, the author and col- leagues 4,9 used widefield fundus imaging by the Optos system and analyzed the presence of staphyloma by examining pig- mentary abnormalities along the upper edge of staphyloma. However, the disadvantage of widefield imaging lies in a lack of 3D information. To solve these issues, we are conducting ongoing stud- ies using a prototype ultra-widefield OCT by Canon Inc. (Tokyo) in our institute. In the near future, this technique will become a cost-effective and more available tool to evalu- ate the presence and types of staphyloma. Different from 3D MRI, widefield OCT can also visualize how the retina and optic nerve are damaged by eye deformity (Figure 5). is is important because it can demonstrate the exact cause of vision-threatening complications in pathologic myopia. CHARACTERISTICS OF POSTERIOR STAPHYLOMA Prevalence Because detection methods differ among various studies, making a direct comparison to discern the prevalence of staphyloma is difficult. e prevalence of staphyloma tends to increase with an increase of axial length in general. Curtin 10 used stereoscopic funduscopy and reported that the staphy- loma was present in 4.8% of the eyes with axial length of 27.5 mm to 28.4 mm. Its prevalence increased to 32.9% in the eyes with axial length between 29.5 mm to 30.4 mm. CLASSIFICATION Curtin's Classification Based on stereoscopic fundus observations, Curtin 1 classified posterior staphylomas in eyes with pathologic myopia into 10 types (Figure 6). Types I to V were considered primary staphylomas and types VI to X were combined staphylomas. is is the most frequently used classification; however, it is Figure 2. Fundus photo with staphyloma (both 50 degree and Optos). A. A 50-degree photo of right fundus shows diffuse chorioretinal atrophy, however, the presence of staphyloma is not obvious. B. Widefield fundus image by Optos clearly shows the border of wide staphyloma (outlined by arrowheads). Figure 3. Steepened scleral curvature by OCT, which is confused with staphyloma. Swept-source OCT image across the fovea and the optic nerve shows the scleral curvature is steepened. However, there is no outpouching of the limited area of posterior sclera, suggesting posterior staphyloma. Figure 4. 3D MRI images of the globe. A. 3D im- ages are created by volume rendering based on T2-weighed image of MRI. en, the images of the eye are extracted. B and C. 3D MRI images of an emmetropic eye. e emmetropic eye is spherical and symmetric in the images viewed from the inferior (B) and nasal (C) positions. D through F. 3D images of the eye with pathologic myopia and posterior staphyloma. Outpouching of the posterior segment, suggesting staphyloma is observed in the images viewed from inferior (D), nasal (E), and back positions. (F).