Dome-Shaped Macula

Imamura and associates reported interesting findings on sclera thickness variations in the macula of myopic eyes. We also agree that the location of ocular expansion (staphyloma) may be more complex than currently conceived. However, their attempt to derive the process of emmetropization from local mechanical eye growth in staphyloma needs to be elucidated further. Staphyloma is a fundamental feature of pathologic myopia and should be differentiated from physiologic myopic progression. In our opinion, the dome-shape macula may be a feature of a complicated staphyloma type or a variant of inferior staphyloma, particularly in mild myopic eyes. The margins of an inferior staphyloma often involves the macula area and causes macular complications such as retinal pigment epithelium (RPE) changes or serous retinal detachment (sRD). Interestingly, in the original dome-shape macula report by Gaucher and associates, all representative cases showed typical features of tilted disc syndrome, which is known frequently to accompany inferior staphyloma. Also, refractive errors in their cases were much less myopic than those of Imamura and associates.

In comparison with Gaucher and associates’ series, Imamura and associates included more elderly patients with higher degrees of myopia. Curtin reported that the incidence of complicate types of staphyloma increase with age and axial length. We consider the possibilities of these unique macular features in Imamura and associates’ series as being secondary features in complicated types of staphyloma. For instance, posterior pole plus macular (Curtin type VI), posterior pole plus peripapillary (type VII or IX), or posterior pole plus inferior staphyloma could show macular elevations in optical coherence tomography (OCT). Staphyloma is defined as an abnormal local protrusion of thin sclera. Considering that the sclera is thinnest at its peak protrusion area, thicker sclera in the macular area in such complicate types could be explicable. It is difficult to define a reference contour of the eye; therefore, extent or types of staphyloma are determined by their margin and slope. However, even this is difficult, especially in cases with large and shallow boundaries or complicated staphyloma. With limitations in scan range in current OCT technology, it is not possible to describe the overall contour of a staphyloma.

Concerning the origin of subretinal fluid, Imamura and associates suggested a fluid barrier mechanism caused by the thickened sclera. However, this may be related to changes along the margin of the staphyloma. Gaucher and associates found RPE atrophic changes in all cases, and mild myopic cases (related to inferior staphyloma) showed a higher incidence of sRD compared with highly myopic cases. In complicated staphyloma, such sole sRD is not a common feature, but usually is complicated with retinoschisis or macular hole. Also, interestingly, the presence of sRD were found to be not as common in Imamura and associates’ cases. Concerning the pathophysiologic features of such changes, we suggest that the term scleral compression maculopathy , which involves compressive changes of the choroid and choriocapillaris and resultant secondary RPE damages, previously described by Green, may be more relevant.

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Jan 16, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Dome-Shaped Macula

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