Retinoschisis (RS), a generally benign condition, is characterized by splitting of layers in the neurosensory retina, typically with elevation of the inner layers in the peripheral part of the retina.1 It is not to be confused with retinal detachment (RD), in which the entire retina separates from the underlying retinal pigmented epithelium. Although clinical observation is sufficient for most cases of RS, early diagnosis and treatment are warranted in RD, a condition that most often requires surgery, in order to prevent permanent visual loss.1–3 Several clinical features can help differentiate RS from RD, such as a more transparent, less mobile, and less wrinkled surface than is seen in full-thickness RD. However, in many cases, especially long-standing RD, clinical features are not enough to distinguish RS from RD.
Spectral-domain optical coherence tomography (SD-OCT) is considered the gold standard for diagnosing RS, as it produces high-resolution imaging of the various retinal layers in which the split in the outer plexiform layer can be visualized.4,5 In contrast, RD will appear on SD-OCT as a separation of the neurosensory retina from the retinal pigment epithelium (RPE). The main limitation of OCT is the limited ability to visualize peripheral lesions, which requires both an experienced technician and a cooperative patient. Even under optimal conditions when retinal lesions anterior to the equator can be detected on OCT, the image quality and resolution may not be sufficient for differential diagnosis.6
Ultrasonography (US) has been found helpful in the diagnosis of RS, even detecting RS that was not identified by OCT.7 On US B-scan, RS usually appears as a smooth, thin, sharply demarcated, dome-shaped, or relatively flat nonmobile membrane. RS differs from RD in its more focal, smooth and thin character, its lack of mobility and its bilaterality.8 However, these signs can be easily missed.
Agarwal et al. applied a novel technique that enhances ultrasonographic images by using a high-resolution US B-scan probe (20 MHz) placed directly on the cornea (open eyelid). Although this method identifies the various retinal layers, enabling precise differentiation of RS from RD,6 it not only requires special equipment not commonly available and a very skilled technician, but it also does not permit imaging of the pars plana area, where RS usually originates. Ultrasound biomicroscopy (UBM) is a noninvasive, painless imaging tool9 used mainly in the diagnosis of anterior segment disorders but has proven useful for visualization of the pars plana and peripheral retina.10 Mannino et al. used UBM to study a case of degenerative RS and described several morphologic features, with emphasis on the relationship between pars plana cysts, cystoid degeneration, and peripheral RS,11 Recent advances in UBM capabilities have significantly improved the visualization of ocular structures with less difficulty. We describe our experience with the bag/balloon UBM imaging technique to identify and describe new features of RS that may be useful in diagnosing the condition.
Patients and Methods
This retrospective study was conducted in the ophthalmology department of a large municipal medical center following approval from the institutional review board in accordance with the tenets of the Declaration of Helsinki. Clinical data and UBM, US B-scan, and SD-OCT images were collected from the medical records of subjects diagnosed with RS and RD from August 2014 through August 2017 who had undergone UBM exam prior to any intervention and met the following criteria: RD cases with clearly visible retinal hole or tear confirmed surgically, and RS cases that exhibited no progression for at least 6 months following diagnosis. Excluded were cases with ocular comorbidity that might affect the diagnosis or imaging interpretation, cases in which it was not possible to ascertain definite diagnosis by clinical examination and/or OCT imaging, and cases with low-quality UBM scans that precluded definitive diagnosis. When involvement was bilateral, one eye was randomly chosen for analysis. All images (UBM, US B-scan, and SD-OCT) were obtained on the same day.
SD-OCT images were obtained with the Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany). The US B-mode and UBM examinations were performed using the Aviso S (Quantel Medical, Clermont-Ferrand, France) at 10 MHz and 50 MHz, respectively. US B-scan was performed in contact with the conjunctiva based on a technique previously described.12 UBM was performed with the bag/balloon technique as described in our previous paper,13 using vertical, horizontal, transverse, and longitudinal scans for each quadrant. This method allowed visualization of the anterior retina up to the equator.
All images (eg, UBM, US B-scan, and SD-OCT) were obtained on the same day. Images were analyzed by two independent, masked observers (MN and AL). On SD-OCT, individual retinal layers were assessed to locate the plane of separation of the retina. RS was defined as a split at the level of the outer plexiform layer (OPL) that separated it from the inner nuclear layer and/or the outer nuclear layer, with or without the presence of bridging pillars.4,5 RD was identified as the separation of the neurosensory retina from the retinal pigment epithelium (RPE).4 Clinical fundus examination combined with SD-OCT was considered the gold standard for the diagnosis of RS and RD. US B-scan images were divided into three groups according to the structure of the lesion: elevated, flat, membranous; dome-shaped; and irregular (Figure 1). The presence of intraretinal cysts was also recorded. UBM images were evaluated for the presence of intraretinal pillars, retinal layers split, and intraretinal cysts (Figure 2). Visualization of retinal tears was also noted.
Sample images for ultrasonography B-scan retinal structures categorized as flat, membranous-shaped (a), dome-shaped (b), and irregular membranous-shaped (c).
Sample images of ultrasound biomicroscopy retinal structures: Retinal layers split (a), intraretinal pillars (b), and intraretinal cysts (c).
The 48 eyes of 48 cases that met the inclusion criteria included 25 diagnosed as RS and 23 as RD. Mean age was 55.9 years ± 17.6 years, and the majority of cases were male (75%). Age at diagnosis was similar in the two groups. There were significantly more females in the RS group (P = .019; odds ratio = 7.0; 95% confidence interval, 1.3–36.7).
Diagnosis of RS was confirmed by OCT in 16 (64%) cases; the image was unavailable in four (16%) cases, and the area in question was too peripheral in five cases (20%) to enable visualization by OCT. On US B-scan images (Figure 3), the RS cases had dome-shaped and flat membrane-shaped cases in nearly equal rates, and there were no cases with irregular structure. In comparison, the RD cases had equal rates of irregular structure and flat-membranous shape. Intraretinal cysts were detected in five (20%) RS cases and in none of the RD cases. According to UBM (Figure 4), “retinal layers split” was the most common finding in the RS group (72%), followed by intraretinal pillars (64%) and intraretinal cysts (36%). No such findings were observed in the RD group. Retinal tears were detected by UBM only in five RD cases (21.7%). Differences were found to be statistically significant overall (P < .001); however, in a subgroup analysis of cases with membranous shape according to the US B-scan, only retinal layers split and intraretinal pillars remained significant. Figure 5 displays multi-imaging case samples of a retinoschisis and retinal detachment for comparison.
Rates of ultrasonography (US) B-scan findings in retinoschisis (RS) and retinal detachment (RD).
Rates of ultrasound biomicroscopy (UBM) findings in retinoschisis (RS) and retinal detachment (RD).
Comparison of multi-imaging sample cases of retinoschisis (a–d) and retinal detachment (e–h) showing infrared (a, e), optical coherence tomography (OCT) (b, f), ultrasonography B-scan (c, g), and ultrasound biomicroscopy (UBM) (d, h) images. The UBM image of the retinoschisis case (d) shows both splitting of the retinal layers (arrow) and intraretinal pillars (arrowheads), whereas the UBM of the retinal detachment case displays a single detached layer. These findings correlate well with the OCT image.
We describe several morphologic findings unique to RS that can help differentiate it from RD. Although both RD and RS have distinctive clinical features, some cases can be highly challenging even to the most experienced clinician. Several tests are available for further attempts to differentiate between the two entities, including indirect ophthalmoscopic perimetry to identify an absolute scotoma,14 laser photocoagulation,15 and examination with scleral indentation,16 but their sensitivity is not sufficient to accurately identify or rule out RS.4,5,17 The advent of SD-OCT made it possible to obtain quality scans that can help detect RS with high levels of accuracy. Previously described differences between RS and RD by UBM imaging include the presence of a single thin layered echo in RS as opposed to a thicker bi-layered echo in RD.10,11 Retinal cysts and microcysts were also reported. However, the detection of distinctive features in those studies was limited by the extreme discomfort caused to the patient by the open-shell technique, in addition to the difficulty of the tool to visualize areas posterior to the limbus. Conclusive differentiation between RS and RD by UBM was further limited in these reports by the absence of an RD group for comparison.
The high-resolution bag/balloon UBM technique, described here for what appears to be the first time for the differential diagnosis of RS and RD, yielded three UBM features unique to RS: splitting of the retinal layers, intraretinal pillars, and intraretinal cysts. The first two were the most frequent findings, detected in 18 (72%) and 16 (64%) cases, respectively. These newly described findings are reminiscent of the appearance of the retina on OCT, which illustrates the pathological separation between retinal layers that occurs in RS. Neither of the three features was found in any of the RD cases, pointing to the effectiveness of UBM to differentiate between the two conditions. Intraretinal cysts were also uniquely visualized in RS, but only in a relatively small number of cases (n = 9; 36%).
The superiority of the bag/balloon UBM technique to OCT and US B-scan images is underscored by our findings with the latter two methods. OCT confirmed the diagnosis of RS in 16 of the 25 cases: images showed splitting of the neurosensory retina in all 16, in agreement with previous studies.17,18 However, OCT imaging was not possible in one-fifth of the cases due to the anterior location of the pathology. US B-scans did detect distinctive sonographic features of RS, including dome-shaped retina and intraretinal cysts, but nearly half of the cases lacked both features, precluding definitively distinguishing them from RD. Although diagnosis of RS was possible by clinical examination in these cases, it is evident that one cannot rely solely on OCT and US to make the diagnosis of RS.
Limitations of the study must be mentioned. Although we present the largest series to date of UBM imaging in RS cases and the first to be assessed by the modern balloon technique, larger sample size is needed to determine the prevalence and predictive value of UBM findings in RS. In addition, although all images were acquired in the customary fashion, the retrospective nature of the study precluded having control over the sonographic technique. Nevertheless, the fact that none of the features found in the RS cases were observed in any of the RD cases supports the contention that they are pathognomonic for RS. It must also be noted that the technical expertise required to detect the distinctive features described herein with the method can be difficult, especially for an inexperienced operator.
Despite these limitations, our findings document that UBM is a noninvasive, safe, and well-tolerated diagnostic tool can assist in diagnosis of RS. Its utility is most important in cases of undetermined diagnosis, especially those in which imaging by SD-OCT is not possible or the images are not of sufficient quality. The complete lack of similar findings in RD cases further strengthens the reliability of USB in diagnosis of RS. Further studies are needed to examine whether retinal layer splitting, intraretinal pillars, and intraretinal cysts occur in peripheral retinal degenerations other than RS, and to determine their predictive value.
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