Structural Grading of Foveal Hypoplasia Using Spectral-Domain ...

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Figure 2. A, Optical coherence tomography scan showing a normal fovea with description of the normal foveal elements. Optical coherence tomography scans showing the spectrum of foveal hypoplasia seen in various conditions, including: (B, C) albinism, (D, E) associated with PAX6 mutations, (F, G) isolated cases, and (H, I) an atypical form of foveal hypoplasia seen in achromatopsia. A hyporeflective zone (cavitation) is also seen (I) that is a sign of cone photoreceptor degeneration. Both foveal hypoplasia and fovea plana were seen in all disorders except the achromatopsia, which results in an atypical form of foveal hypoplasia with a shallower pit, incursion of the plexiform layers, and disruption of the inner segment (IS)/outer segment (OS) junction. INL inner nuclear layer; NFL nerve fiber layer; ONL outer nuclear layer. morphologic OCT scan, and (3) it can be applied to most disorders associated with foveal hypoplasia. The study also showed that achromatopsia can be associated with foveal hypoplasia, although it is associated with atypical features such as IS/OS disruption and ONL thinning, which are signs of photoreceptor degeneration, reduced retinal thickness (RT), and a deeper foveal pit in comparison with the typical forms of foveal hypoplasia. From a developmental perspective, each grade suggests developmental arrest of the 3 key events to varying degrees, as shown in Figure 1. All patients with foveal hypoplasia in this study had incursion of the plexiform layer posterior to 1656 Ophthalmology Volume 118, Number 8, August 2011 the foveola, suggesting that pit formation was incomplete in all patients. A partial displacement of the inner retinal layers results in a rudimentary pit, as encountered with grade 1 foveal hypoplasia and atypical foveal hypoplasia. This process has failed to occur in grades 2, 3, and 4 of foveal hypoplasia. Lengthening of the OS is a sign of cone photoreceptor specialization, and this occurs to some extent in grades 1 and 2, but not grades 3 and 4. Lengthening of the OS can occur in the absence of a foveal pit, as seen in grade 2 foveal hypoplasia, and also as suggested by Marmor et al. 7 However, no cases where a foveal pit was present with no OS lengthening (i.e., all patients with a foveal pit had OS
Thomas et al Structural Grading of Foveal Hypoplasia Figure 3. A, Illustration showing the unique features of a normal fovea detectable on optical coherence tomography. B, Illustration of typical and atypical grades of foveal (this is a CE) hypoplasia. All grades of foveal hypoplasia had incursion of inner retinal layers. Atypical foveal hypoplasia also had incursion of the inner retinal layers. Grade 1 foveal hypoplasia is associated with a shallow foveal pit, outer nuclear layer (ONL) widening, and outer segment (OS) lengthening relative to the parafoveal ONL and OS length, respectively. In Grade 2 foveal hypoplasia, all features of grade 1 are present except the presence of a foveal pit. Grade 3 foveal hypoplasia consists of all features of grade 2 foveal hypoplasia except the widening of the cone outer segment. Grade 4 foveal hypoplasia represents all the features seen in grade 3 except there is no widening of the ONL at the fovea. Finally, an atypical form of foveal hypoplasia also is described in which there is a shallower pit with disruption of the inner segment/outer segment (IS/OS) junction, possibly a sign of photoreceptor degeneration. The atypical form of foveal hypoplasia is seen with achromatopsia, whereas grades 1 through 4 are seen with albinism, PAX-6 mutations, and isolated cases. ELM external limiting membrane; GCL ganglion cell layer; INL inner nuclear layer; IPL inner plexiform layer; OPL outer plexiform layer; RNFL retinal nerve fibre layer; RPE retinal pigment epithelium. 1657
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