Purpose
To examine the posterior anatomic structure of eyes with dome-shaped macula using enhanced depth imaging spectral-domain optical coherence tomography (EDI-OCT).
Design
Retrospective observational case series.
Methods
Patients with dome-shaped macula, a condition defined as convex elevation of the macula as compared with the surrounding staphylomatous region in a highly myopic eye, were identified through routine examinations using optical coherence tomography (OCT). EDI-OCT was used to examine their posterior anatomic changes. The scleral thickness was measured from the outer border of the choroid to the outer scleral border under the fovea and 3000 μm temporal to the fovea.
Results
The mean age of the 15 patients (23 eyes) was 59.3 (± 12.2) years, and the mean refractive error was -13.6 (± 5.0) diopters. The best-corrected visual acuity ranged from 20/15 to 20/800 (median: 20/30). Eight patients (53%) had dome-shaped macula bilaterally. The mean subfoveal scleral thickness in 23 eyes with dome-shaped macula was 570 (± 221) μm, and that in 25 eyes of 15 myopic patients with staphyloma but without dome-shaped macula was 281 (± 85) μm ( P < .001) even though both groups had similar myopic refractive error. The scleral thickness 3000 μm temporal to the fovea was not different in the 2 groups.
Conclusions
Dome-shaped macula is the result of a relative localized thickness variation of the sclera under the macula in highly myopic patients, and it cannot be categorized into any of the known types of staphyloma. This finding suggests the ocular expansion in myopia may be more complex than previously thought.
Dome-shaped macula was originally described by Gaucher and associates as a convex protrusion of macula within a staphyloma in highly myopic patients as diagnosed by optical coherence tomography (OCT). This had been an unexpected phenomenon of high myopia, because axial myopia usually involves lengthening and stretching of the eye. Gaucher and associates considered that the convexity of the macula could have been the result of thickening of the choroid in the macular area, although the authors could not demonstrate this by ultrasonography. Subsequently, scleral infolding through collapse of the posterior portion of the eye wall or vitreomacular traction were proposed as causes of dome-shaped macula.
Recently a method to obtain enhanced depth imaging optical coherence tomography (EDI-OCT) has been developed that enables the cross-sectional structure and thickness of the choroid to be evaluated. If dome-shaped macula is caused by thickened choroid as seen, for example, in central serous chorioretinopathy, then a thick choroid should be detected in the eyes with dome-shaped macula using EDI-OCT. In addition, it was noticed that the sclera and even anterior orbital tissue could be seen in some highly myopic patients with EDI-OCT. Here EDI-OCT is used to visualize posterior anatomic relationships in eyes with dome-shaped macula.
Patients and Methods
The diagnosis of dome-shaped macula was based on the presence of a convex elevation of the macula as per Gaucher and associates. Cases of dome-shaped macula were determined from medical record evaluation of myopic patients. The patients were seen either at the Vitreous-Retina-Macula Consultants of New York (New York, New York, USA) from September 1, 2008 through January 31, 2010 or at the Fukushima Medical University School of Medicine (Fukushima, Japan) from February 1, 2009 through December 31, 2009. The affected patients were evaluated with a complete ophthalmologic examination including best-corrected visual acuity, intraocular pressure, color photography, and EDI-OCT. Original refractive errors were identified for the eyes having undergone cataract or refractive surgery.
The OCT images were obtained using the Spectralis HRA+OCT (version 1.5.12.0, then later version 1.6.2.0; Heidelberg Engineering, Heidelberg, Germany). EDI-OCT was originally obtained by positioning a spectral-domain OCT device close enough to the eye to acquire an inverted image. Seven sections, each composed of 100 averaged scans, were obtained within a 5 × 30-degree rectangle to encompass the macula. More recently, the EDI-OCT feature was built into the Heidelberg software as a user-selectable feature. To perform EDI-OCT the EDI button is selected at the beginning of the scanning procedure. The horizontal section through the center of the fovea was used for the measurements of 1) thickness of the choroid, defined as the distance from the outer border of the hyperreflective line corresponding to the retinal pigment epithelium to the inner scleral border; and 2) thickness of sclera, defined as the distance between its inner and outer borders. When the contour of fovea is not clear, the image most likely to represent foveal scan is chosen. The sclera was identified in OCT images as a highly reflective multilaminar layer under the choroid. In 2 eyes in which the outer borders of sclera exceeded the posterior distance imaged within the EDI-OCT scan or were not clearly visible, the greatest thickness that could be measured was substituted. Highly myopic eyes without dome-shaped macula that underwent EDI-OCT were reviewed. Scleral thicknesses 3000 μm temporal to the fovea were measured in the eyes with and without dome-shaped macula, in which the sclera was scanned 3000 μm temporal to the foveal center. The data obtained were analyzed with frequency and descriptive statistics. The subfoveal scleral thickness was analyzed using the Mann-Whitney U test. A P value less than .05 was considered significant.
Results
There were 23 eyes with dome-shaped macula in 15 patients with high myopia, and they had a mean age of 59.3 (SD ± 12.2) years. Eight patients (53%) had bilateral dome-shaped macula; 10 patients (67%) were female. The corrected visual acuity ranged from 20/15 to 20/800 (median: 20/30). The mean refractive error was -13.6 (± 5.0) diopters (D) (range: -5.0 to -26.0 D, median: -12.5 and -14.8 D). The mean intraocular pressure of the eyes with dome-shaped macula was 15 (± 3) mm Hg. Eleven eyes had a history of choroidal neovascularization (CNV), with 6 being treated by photodynamic therapy and 5 with anti–vascular endothelial growth factor injection. One eye had both treatments and another had an untreated disciform scar. The mean refraction error of the highly myopic eyes without dome-shaped macula was -11.7 (± 5.5) D (range: -5 to -30 D), which was not significantly different from those with dome-shaped macula ( P = .228).
The mean subfoveal scleral thickness measured in the eyes with dome-shaped macula was 570 μm (SD ± 221 μm), and the thickness in 25 eyes with high myopia but without dome-shaped macula was 281 μm (± 85 μm) ( P < .001). Eyes with dome-shaped macula did not have any evident distortion of the images of the retina or choroid, making the possibility of image distortion or abnormalities of image processing as the cause of the observation unlikely. The mean subfoveal scleral thickness in the eyes with dome-shaped macula was not different in those with CNV and without (547 μm vs 587 μm; P = .668). Representative EDI-OCT images of myopic eyes without dome-shaped macula are shown, and these demonstrate concave contours of both inner and outer borders of the sclera ( Figure 1 ). Tissue posterior to the sclera, presumably orbital fat, was visible in 17 of 25 eyes (68%) without dome-shaped macula ( Figure 1 ). The mean scleral thickness 3000 μm temporal to the fovea was available for 14 eyes in those with dome-shaped macula and in 11 without. The main reasons for lack of information about the scleral thickness 3000 μm temporal to the fovea related to the curvature of the eye in highly myopic patients; spectral-domain OCTs have a limited vertical range in which they can image the eye without distortion or image folding. The scleral thickness 3000 μm temporal to the fovea was not different between the eyes with dome-shaped macula, 337 μm, and eyes without dome-shaped macula, 320 μm ( P = .707). Representative OCT images of the eyes with dome-shaped macula are shown ( Figures 2, 3 and 4 ). Note the many lamellae in the sclera within the regional thickening of the sclera as opposed to the small number of lamellae contained in the thinner peripheral sclera. This also argues against an abnormality of the imaging process as being the cause of the subfoveal thickening. The subfoveal choroidal thickness of the dome group was 58.1 ± 43.8 μm, which was slightly thicker than those eyes without dome-shaped macula (35.7 ± 32.0 μm) ( P = .048). Subretinal fluid was detected in 2 of 23 eyes (9%) and sub-RPE fluid in 1 eye with dome-shaped macula.
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