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Department of Ophthalmology, Asahikawa Medical College, Asahikawa, Japan
Keywords: optical coherence tomography; retinoschisis
Juvenile X linked retinoschisis is a congenital X linked recessive retinal disorder, the characteristic funduscopic findings of which are a silver-grey retinal reflex, foveal retinoschisis, and peripheral retinoschisis. Electroretinograms (ERGs) typically record a reduced b-wave amplitude with relative preservation of the a-wave amplitude. Visual acuity (VA) usually deteriorates slowly until the patient is about 20 years of age, stabilises around 0.20.5, and sometimes deteriorates further because of macular degeneration.1–4
Podoleanu and associates developed a novel integration of scanning laser ophthalmoscopy (SLO) and optic coherence tomography (OCT)—three dimensional optical coherence tomography (3-D OCT).5 Using transverse scanning, typical for SLO, the instrument simultaneously produces SLO and interferometric OCT images.6 We can obtain both cross sectional scans (B-scans) as with conventional OCT and transverse scans (C-scans) using 3-D OCT. This is the first report of 3-D OCT findings in juvenile X linked retinoschisis.
Case report
A 7 year old boy presented with VA of 0.5 and 0.6 in the right and left eyes, respectively. Funduscopy showed a silver-grey retinal reflex and cartwheel-like macular degeneration bilaterally. Peripheral retinoschisis was absent. ERGs were recorded and dark adaptation testing was performed. Single flash ERG showed decreased b-wave amplitude, which was consistent with the diagnosis. Dark adaptation revealed a decreased curve overall.
The B-scan findings of 3-D OCT (fig 1) showed the retina split into four distinct planes. Two wide hyporeflective spaces split the retina. Anteroposterior or oblique linear columns were seen across the superficial wide hyporeflective space, forming a bridge that was not found in the fovea. These columns are considered to be Muller cells by OCT and histological studies.3,7,8
Figure 1 B-scans of 3-D OCT. Two wide hyporeflective spaces split the retina. Anteroposterior or oblique linear columns form a bridge across a superficial wide hyporeflective space. In the same layer, there is a large cystoid space in the fovea (line N). This layer is probably the outer plexiform layer. Deeper cleavage is seen in the parafoveal area but not in the fovea (line P). This layer is probably the outer nuclear layer. Small cystoid spaces (arrowhead) are seen in the superficial parafoveal retina that split the retina (line M). This layer is probably the nerve fibre layer or the ganglion cell layer.
There was a large cystoid space in the fovea connected to the superficial wide hyporeflective parafoveal space. A deeper wide hyporeflective space was in the parafoveal retina but disappeared in the fovea. Small cystoid spaces in the superficial parafoveal retina split the retina. Retinal cleavage involving the fovea was found in the outer plexiform layer. Superficial retinal cleavage was most likely in the nerve fibre layer or the ganglion cell layer. The deep retinal cleavage was in or just around the outer nuclear layer. C-scan findings of 3-D OCT showed the extent of the cleavage planes and the hyporeflective spaces (fig 2). Of particular note, the C-scans showed many columns in a large space (schisis). This is in contrast with the B-scans that showed the spaces between the columns to be cystic spaces. The C-scans provided a better understanding of this pathology.
Figure 2 C-scans of 3-D OCT. C-scans M, N, and P correspond to the same depth of the B-scans (fig 1) in lines M, N, and P. *The location of the fovea. (M) A large cystic space is seen in the fovea and the retina, which includes the small cystic spaces. The small spaces found in the B-scan are confirmed in the C-scan. (N) This space is equivalent to a superficial schisis and shows the space in the fovea and the columns around it. In B-scan images, the spaces between the columns are hypothesised to be cystic space; however, in C-scan images, these spaces are not cystic, and many columns can be seen in a large space (schisis). (P) This is equivalent to the deeper schisis and shows the hyperreflective area (no schisis) in the fovea and the large space (schisis) around the fovea.
Comment
Recently, conventional OCT findings of foveal schisis were reported1,7 to be in the outer plexiform layer and adjacent nuclear layers. Histopathologically, foveal schisis was reported to occur in the outer plexiform layer,2 although peripheral retinoschisis was found in the nerve fibre layer and ganglion cell layer.3
3-D OCT demonstrated that schisis can occur in any retinal layers in juvenile X linked retinoschisis. We obtained cross sectional and transverse images of the retinoschisis with near histological precision that showed the details of the inner retinal structures and the extent of the schisis. 3-D OCT is useful to evaluate, non-invasively, the retinal pathology and follow patients with juvenile X linked retinoschisis.
References
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