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X-linked retinoschisis (XLRS) is the most common cause of juvenile-onset macular degeneration in male patients. XLRS is a bilateral, recessively inherited vitreoretinal degeneration characterized clinically by stellate, spoke-like foveal schisis, vitreous veils, peripheral retinoschisis and decreased b/a-wave ratio of the electroretinogram.1

The F-10 (Nidek, Gamagori, Japan) is a new, commercially available scanning laser ophthalmoscope (SLO) that is equipped with four laser sources emitting blue, green, red and infrared light. The light returning from the fundus to the SLO consists of direct back-reflected light and multiple scattered light rays.2 The dark-field mode uses an aperture with a central stop (ring-shaped aperture) that can collect reflections from the scattered light from the retinal tissue. This property allows it to obtain images of deeper retinal structure with infrared light.

The newly developed retro-mode is a modification of the dark-field mode, and it uses a laterally oriented oval-shaped opening with a central stop. With the conventional ring-shaped aperture, the fundus camera receives light from multiple directions. In contrast, the retro-mode collects scattered light from only one direction through the laterally oriented opening, and rays from other directions are blocked.2–4 This blocking of the reflection from the other directions creates a highlighted shadow-like image. Because the detector in the camera receives light from a limited angle in the retro-mode, light from a limited angle casts shadows as if viewing the translucent retinal tissue with laterally projected light. Thus, the retro-mode provides clearer pseudo-three-dimensional images than the conventional dark-field mode.3,4 It has been reported that the retro-mode with infrared light can clearly delineate cystoid spaces of cystoid macular oedema2 and invisible sites of subthreshold micropulse laser application as dark spots.4Figure 1 shows the retro-mode images from a normal subject.

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Figure 1. Colour fundus photographs and scanning laser ophthalmoscopic (SLO) images in the retro-mode from a 25-year-old normal woman. Images in the left column show images of the right eye and right column of the left eye. The best-corrected visual acuity was 1.0 in both eyes. (a, b) Ring reflex is observed in the macula. (c, d) Images obtained by the SLO in the retro-mode show no remarkable change except for mottling of the background reflex.

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Most recently, Tanaka et al.3 reported that the retro-mode images had a characteristic fingerprint pattern at the area corresponding to the macular retinoschisis in highly myopic eyes. This fingerprint pattern consisted of radiating retinal striae centered on the fovea and many light dots or linear reflexes around the radiating striae. The radiating retinal striae were imaged as well-defined thin lines and did not have a cystoid appearance. The site of these alterations corresponded to that of the macular retinoschisis obtained by multiple optical coherence tomography (OCT) scans. The authors concluded that the retro-mode could be used to determine the presence and extent of a macular retinoschisis.

In eyes with XLRS, it is occasionally difficult to detect a foveal schisis ophthalmoscopically. We report a case of XLRS with stellate spoke-like foveal schisis that was not clearly detected by ophthalmoscopy and in colour fundus photographs. However, the foveal schisis was clearly delineated in the SLO retro-mode images.

A 21-year-old man diagnosed with XLRS was examined. His vision had been subnormal since the age of 6 years when he failed a school visual screening test. His younger brother was also diagnosed with XLRS. His best-corrected visual acuity was 0.7 Oculus Dexter (OD) and 0.3 Oculus Sinister (OS). A peripheral retinoschisis was not found, but vitreous veils were seen in both eyes. The b/a-wave ratio of the electroretinogram elicited by a bright white flash was reduced. Stellate spoke-like foveal schisis was indistinct ophthalmoscopically and in the colour fundus photographs (Fig. 2a,b). However, the images obtained by the SLO in the retro-mode clearly delineated the stellate spoke-like foveal schisis (Fig. 2c,d). The spectral-domain OCT images showed tissue pillars connecting the schisis cavities, giving the images a ladder-like appearance (Fig. 2e,f).

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Figure 2. Colour fundus photographs, scanning laser ophthalmoscopic (SLO) images in the retro-mode and spectral-domain optical coherence tomographic (OCT) images from a 21-year-old man with foveal schisis due to X-linked retinoschisis. Images in the left column show images of the right eye and right column of the left eye. The best-corrected visual acuity was 0.7 in the right eye and 0.3 in the left eye. (a, b) Stellate spoke-like foveal schisis is indistinct in the colour fundus photographs. (c, d) Images obtained by the SLO in the retro-mode clearly delineate the stellate spoke-like foveal schisis (white arrows). (e, f) OCT images show tissue pillars connecting the schisis cavities, giving the images a ladder-like appearance. The central foveal area is more elevated than the parafoveal retina.

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The images which we obtained from our XLRS patient with the SLO in the retro-mode had radiating retinal striae centred on the fovea. These striae were indistinct ophthalmoscopically and not seen in the colour fundus photographs. Tanaka et al.3 stated that they could not determine the mechanism causing these radiating retinal striae to correspond to macular retinoschisis on the retro-mode images.

OCT is a valuable way to diagnose XLRS. Younger patients frequently show tissue pillars connecting the borders of the schisis cavities, giving the OCT image a ladder-like appearance. Although OCT can provide valuable information on the morphologic features of foveal schisis, it is often difficult to detect the entire extent of the schisis.3 The foveal schisis occurs predominantly in the inner nuclear layer but it can also be found in different layers of the neurosensory retina, that is, the outer nuclear layer/outer plexiform layer and occasionally in the retinal nerve fiber layer.5 Therefore, even an en-face OCT image may not show all the schisis cavities in one image. With the SLO in the retro-mode, all of the schisis cavities can be detected in one image regardless of the location of schisis cavity because the scattered light passes through all retinal layers.

In conclusion, combining the SLO retro-mode images with those obtained by OCT should provide valuable information on the pathophysiological features of foveal schisis.

References

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  2. References
  • 1
    Gregori NZ, Berrocal AM, Gregori G et al. Macular spectral-domain optical coherence tomography in patients with X linked retinoschisis. Br J Ophthalmol 2009; 93: 3738.
  • 2
    Yamamoto M, Mizukami S, Tsujikawa A, Miyoshi N, Yoshimura N. Visualization of cystoid macular oedema using a scanning laser ophthalmoscope in the retro-mode. Clin Experiment Ophthalmol 2010; 38: 2736.
  • 3
    Tanaka Y, Shimada N, Ohno-Matsui K et al. Retromode retinal imaging of macular retinoschisis in highly myopic eyes. Am J Ophthalmol 2010; 149: 63540.
  • 4
    Ohkoshi K, Tsuiki E, Kitaoka T, Yamaguchi T. Visualization of subthreshold micropulse diode laser photocoagulation by scanning laser ophthalmoscopy in the retro mode. Am J Ophthalmol 2010; 150: 85662.
  • 5
    Yu J, Ni Y, Keane PA, Jiang C, Wang W, Xu G. Foveomacular schisis in juvenile X-linked retinoschisis: an optical coherence tomography study. Am J Ophthalmol 2010; 149: 9738.