Optical coherence tomography (OCT) was first introduced into clinical practice in the mid-1990s, with the earliest scientific reports describing its use in retinal disease published around 1995.1,2 Since then, OCT has become instrumental in the diagnosis, management, and follow-up of most retinal diseases.3 However, only more recently, has OCT emerged as an important tool for the assessment of rhegmatogenous retinal detachment (RRD). Although many structural changes have been described on OCT, their clinical and pathophysiological relevance are still being elucidated. OUTER RETINAL CORRUGATIONS Among the many OCT findings described in the setting of retinal detachment, one of the most important is the presence of outer retinal corrugations (ORCs). ORCs were first reported by Hagimura et al. in 2000 and are undulations restricted to the outer retina.4 In this study, ORCs were found to be more prevalent in detachments of greater height, a relationship whose mechanistic basis has only recently been better understood. As OCT technology improved, multiple groups expanded upon these observations and in the past few years ORCs have evolved from being a descriptive OCT finding to a key clinical biomarker of RRD pathophysiology. Using OCT scans, Muni et al. were able to investigate on the pathophysiology and biomechanics of the detached retina and developed mechanical models to explain the formation of ORCs.5 The presence of corrugations is now recognized as a marker of rapidly progressive (“dysregulated”) detachments. This observation was made possible by assessing many cases of RRD with and without ORCs. ORCs are absent in small, localized RRDs, irrespective of their time of development Figure 1. Similarly, they are not observed in cases of displaced subretinal fluid or residual subretinal fluid observed in non-drainage procedures Figure 2. In cases treated with pneumatic retinopexy (PnR) or non-drainage scleral buckle, ORCs have been shown to resolve once the causative retinal break stops recruiting subretinal fluid.5 Sequential OCT imaging performed hourly after PnR demonstrated that, as the retina slowly re-approaches the retinal pigment epithelium (RPE), ORCs gradually resolve despite persistent thickening of the bacillary layer prior to complete reattachment Figure 3.6 This year, Mah et al. expanded on these findings, demonstrating that the presence of ORCs is highly predictive of an open retinal break.7 This observation has important clinical implications in the postoperative setting, particularly in eyes with residual subretinal fluid following RRD repair.Figure 1: (a) Wide-field fundus image after laser retinopexy in an eye with an acute localized rhegmatogenous retinal detachment. (b, d, and f) Swept-source optical coherence tomography scan locations with corresponding images (c, e, and g) showing peripheral cross-sectional scans near the horseshoe tears with the absence of outer retinal corrugations, even after an extended period of follow-up, after the barricade laser retinopexyFigure 2: (a) Wide-field fundus image showing rhegmatogenous retinal detachment at postoperative day one with the swept-source optical coherence tomography (SS-OCT) scan location indicated by the white arrowhead. (b) Ultra-widefield guided SS-OCT scan of the previous image showing inferotemporal residual displaced subretinal fluid, after pneumatic retinopexy, without any signs of outer retinal corrugations despite the persistence of vertical ellipsoid zone thickeningFigure 3: (a) Wide-field fundus image showing rhegmatogenous retinal detachment at baseline with a horseshoe tear in the superotemporal quadrant. (b) Baseline swept-source optical coherence tomography scan showing outer retinal corrugations (arrowheads) that improved over two time points in the postoperative period, despite persistent vertical thickening of the ellipsoid zone (c and d)ORCs are also absent in serous or exudative detachments Figure 4. In a prospective multicenter study, ORCs were identified as a negative predictive factor for exudative retinal detachments, with none of the affected eyes demonstrating corrugations.8 Another clinical scenario in which ORCs are absent is slowly progressive or subclinical (“regulated”) RRDs Figure 5, which often occur in myopic or young patients with shallow detachments and an attached posterior hyaloid.9 Even in acute detachments, ORCs are typically absent if the detachment has been present for <48 h.5Figure 4: (a) Wide-field fundus image showing an exudative retinal detachment in the macula of a patient diagnosed with Vogt–Koyanagi–Harada. (b) Swept-source optical coherence tomography cross-sectional scan of the macula showing the absence of outer retinal corrugations, despite vertical ellipsoid zone thickeningFigure 5: (a) Wide-field fundus image showing chronic rhegmatogenous retinal detachment (RRD) at baseline with the swept-source optical coherence tomography (SS-OCT) scan location indicated by the white arrowhead. (b) Vertical SS-OCT scan, indicated in the previous image, without any signs of outer retinal corrugations despite the persistence of vertical ellipsoid thickening. This patient presented with a nasal macula-on RRD from 1 to 7 o’clock with two months of symptoms. (c) Wide-field fundus image showing chronic RRD at baseline with SS-OCT scan location indicated by the white arrowhead. (d) Macular SS-OCT cross-sectional scan without any signs of outer retinal corrugations, despite the persistence of vertical ellipsoid thickening. This patient presented with a shallow inferior macula-off RRD from 2 to 9 o’clock, with 2 to 3 months of symptomsFinally, ORCs are consistently absent at the fovea Figure 6, which is hypothesized to occur from the unique anatomy and morphology of the central Müller cells and the surrounding foveal cones.5 In this region, a distinct abnormality is observed in approximately 25% of RRDs: Bacillary layer detachment (BALAD) Figure 7. BALAD is thought to arise from the inability of this region to form ORCs. The expansion of the outer retina following an RRD creates mechanical stress within the foveal bouquet. Because of the structural constraints of the fovea, this stress cannot be accommodated by corrugation and instead may manifest as BALAD.10Figure 6: (a and b) Baseline SS-OCT scans showing two different eyes with macula-off rhegmatogenous retinal detachment and foveal sparing of outer retinal corrugations (white arrowheads)Figure 7: Optical coherence tomography foveal scans in fovea-off rhegmatogenous retinal detachments depicting the spectrum of structural abnormalities in the fovea: (a) Early minimal non-exudative bacillary layer detachment (BALAD) (arrowhead); (b) Larger BALAD bounded by the external limiting membrane (ELM) and residual inner segments anteriorly and by the ellipsoid zone and residual outer segments (OS) posteriorly, forming a bridge of photoreceptor remnants (arrowhead); (c) BALAD with cleavage planes at the lateral aspects of the foveal bouquet, extending from the outer nuclear layer through the ELM, into the myoid zone. This is visualized as oblique/vertical hyporeflective lines contiguous with the BALAD cavity (arrows). (d) Loss of the Müller cell cone (star) resulting in inner lamellar hole with residual bridge of ellipsoid and OS remnants (arrowhead)Collectively, these clinical observations, together with OCT imaging across a broad spectrum of RRDs, led to the formulation of a mechanistic hypothesis for ORC development. Mathematical modeling demonstrated that ORC formation requires: (1) An acute and progressive exposure of the subretinal space to liquefied vitreous (2) that persists for at least 2 days, and (3) overwhelms the capacity of the RPE to regulate the subretinal space, leading to an extensive detachment.11 Rapidly progressive RRDs result in dysregulation of the subretinal space, with clinical variability largely determined by the rate of inflow and volume of liquefied vitreous entering the subretinal space. This concept is referred to as the “dysregulation theory.” In rapidly progressive detachments, a continuous influx of fluid into the subretinal space results in diffusion-driven hydration of the outer retina. This hydration leads to a lateral expansion and the generation of compressive forces. This also results in a reduction in the elastic modulus of the outer retina relative to the inner retina, effectively softening the tissue and allowing it to be more deformable. Because this lateral expansion occurs within a constrained anatomical space, mechanical instability develops, leading to buckling strain and the formation of compensatory ORCs. Over time, these corrugations progress, increasing in amplitude and thickness.5,11,12 Not only do the ORCs represent a critical pathophysiological component of RRD but they can also affect structural outcomes. Dell’Omo et al. were the first to demonstrate that outer retinal folds (ORFs) may develop postoperatively from preexisting corrugations Figure 8.13 ORFs are partial-thickness folds of the outer retina that manifest on OCT as localized alterations in inner and outer segment reflectivity and typically resolve spontaneously over several months.14 Subsequent studies demonstrated that ORFs have significant clinical implications, as their presence is associated with worse postoperative visual outcomes.15Figure 8: (a) Baseline swept-source optical coherence tomography (SS-OCT) scan showing rhegmatogenous retinal detachment with outer retinal corrugations (white arrowheads). (b) Outer retinal fold (ORF) formation at the site of previous outer retinal corrugations on postoperative SS-OCT (white arrows), that can be better visualized as hyperreflective lines on the en face scan (black arrowheads) using a customized slab (c). The black line demonstrates the cross-sectional scan location of 1B that passes through three ORFsMORPHOLOGIC STAGES OF RETINAL DETACHMENT Although ORCs represent a hallmark OCT feature of RRD, several additional retinal changes precede and follow their development in “dysregulated” detachments. In 2023 Martins Melo et al. comprehensively characterized the sequential morphologic changes that the outer retina undergoes following an RRD.16 With the assistance of swept-source ultrawide-field OCT, the group obtained sequential scans along the most probable direction of RRD progression across multiple cases. The scans were evaluated from the causative retinal break to the posterior edge of the detachment, including the junction between attached and detached retina. This allowed for a clear assessment of the directionality of the RRD progression as well as subsequent validation of the relative duration of these structural changes. Regions closer to the posterior edge represented more acute changes, whereas areas near the retinal break exhibit more longstanding, advanced-stage abnormalities. The stages were characterized based on multiple cases and were categorized into five main stages Figures 9 and 10: Stage 1 is the separation of the neurosensory retina from the RPE with no apparent changes to the bacillary layer. This is rapidly followed by Stage 2, where there is a thickening of the bacillary layer with loss of distinction between the ellipsoid zone (EZ) and interdigitation zone (IDZ). Stage 3 is marked by the formation of ORCs, initially low amplitude (≤50 µm; Stage 3A), progressing to high amplitude ORCs in Stage 3B. Over time, these ORCs lose definition in Stage 4. In some cases, “fused ORCs” start to form with photoreceptor-photoreceptor apposition when ORCs are of higher amplitude. This occurs with concurrent thickening of the bacillary layer and increased hyperreflective dots. Finally, Stage 5 is characterized by patchy or complete loss of photoreceptor segments and thinning of the outer retina.16Figure 9: Baseline swept-source optical coherence tomography foveal scans demonstrating the sequential morphological changes following rhegmatogenous retinal detachment (RRD) with five reproducible stages observed in the parafoveal region. (a) Stage 1 at the junction of the attached and detached retina at the most posterior leading edge of the RRD (arrowhead), defined as a separation of the neurosensory retina from the retinal pigment epithelium, with no apparent changes in the photoreceptor layer. (b) Stage 2 corresponds to a thickening of the photoreceptor layer (arrowhead) that occurs soon after stage 1. (c) Stage 3a in which there are low-frequency outer retinal corrugations (ORCs), progressing to high-frequency ORCs in stage 3b (d); in both images, the different stages are indicated with arrowheads. (e) Stage 4 is characterized by progressive loss of definition of the ORCs, with concurrent thickening of the photoreceptor layer (arrowhead) with/without hyperreflective dots. (f) Stage 5 is characterized by patchy, then complete loss of photoreceptors, which is observed as a moth-eaten appearance of the outer retina (arrowhead) that later progresses to more significant gaps devoid of photoreceptor inner and outer segments (star), corresponding to the final stage of outer retinal degeneration following RRDFigure 10: Baseline swept-source optical coherence tomography scans demonstrating the sequential morphological changes following rhegmatogenous retinal detachment (RRD) with five reproducible stages observed in the mid-periphery. (a) Stage 1 at the junction of the attached and detached retina at the most posterior leading edge of the RRD (arrowhead), defined as a separation of the neurosensory retina from the retinal pigment epithelium, with no apparent changes in the photoreceptor layer. (b) Stage 2 corresponds to a thickening of the photoreceptor layer (arrowhead) that occurs soon after stage 1. (c) Stage 3a in which there are low-frequency outer retinal corrugations (ORCs), progressing to high-frequency ORCs in stage 3b (d); in both images, the different stages are indicated with arrowheads. (e) Stage 4 is characterized by progressive loss of definition of the ORCs, with concurrent thickening of the photoreceptor layer with/without hyperreflective dots. In stage 4, the loss of outer retinal structure is observed as less defined ORCs, which appear either as a homogenous block of tissue if the ORCs are low amplitude (arrow) or as “folds” in the retina with photoreceptor-photoreceptor apposition if the ORCs are high amplitude (arrowheads). (f) Stage 5 is characterized by patchy, then complete loss of photoreceptors, which is observed as a moth-eaten appearance of the outer retina that later progresses to more significant gaps devoid of photoreceptor inner and outer segments (arrowhead), corresponding to the final stage of outer retinal degeneration following RRDIncreasing morphologic stage of RRD is associated not only with worse visual acuity during the first postoperative year, but also with worse photoreceptor integrity on OCT Figures 11 and 12.17,18 Moreover, the morphologic stages of RRD remained an independent predictor of visual and structural recovery even after controlling for duration of vision loss, time to surgery, foveal detachment height, and surgical technique. This remained true even among early stages, where patients with stages 1, 2, and 3A in fovea-involving RRDs had better visual acuity at 1 year than stage 3B, underscoring, once again, the importance of ORCs as a biomarker of structural damage.17Figure 11: Longitudinal progression of LogMAR best-corrected visual acuity at 3, 6, and 12 months per presenting morphologic stage of rhegmatogenous retinal detachmentFigure 12: Baseline morphologic rhegmatogenous retinal detachment stage was assessed at presentation. Postoperative ellipsoid zone (EZ) integrity was assessed as either continuous or discontinuous at 3, 6, and 12 months. Baseline morphologic stage was associated with postoperative EZ integrity (P < 0.00001). Here we show the percentage of patients with discontinuous EZ at 3-, 6-, and 12-month postoperatively. EZ: Ellipsoid zoneBACILLARY LAYER DETACHMENT AND RELATED FOVEAL ABNORMALITIES The fovea represents a notable exception to the typical morphologic progression of RRD. This phenomenon is attributed to the unique cellular architecture of the foveal pit. During embryogenesis, centrifugal displacement of inner retinal layers results in dense central cone packing surrounded by large Müller glia, which form the Müller cell cone (MCC).19 Electron microscopy studies have further demonstrated a distinct population of Müller cells in the fovea that terminate at the outer plexiform layer, in addition to those spanning from the internal limiting membrane to the external limiting membrane (ELM).20 Owing to its unique anatomy, the fovea not only lacks ORCs, but exhibits unique abnormalities of clinical relevance. While corrugations develop in the para- and perifoveal regions in dysregulated RRDs to for the outer retinal the anatomical constraints of the fovea it from However, the hydration may stress within the foveal bouquet, leading to 25% of patients present with BALAD at abnormalities may the of the BALAD from changes or complete of the resulting in a BALAD lamellar hole [Figure This is particularly as of in RRD are associated with BALAD lamellar BALAD develops, several tissue changes may to further instability and loss of the In a large study, Martins Melo et al. demonstrated a spectrum of OCT changes progressing from BALAD to hole (1) of within the layer to central Müller into the BALAD cavity [Figure (2) central outer nuclear layer thinning [Figure (3) loss of the with tissue remnants at the foveal [Figure progressive thinning complete of the tissue that the posterior of the BALAD lamellar hole resulting in a [Figure optical coherence tomography foveal scans of fovea-off rhegmatogenous retinal detachment demonstrating the of a bacillary layer detachment lamellar hole with a residual posterior bridge of photoreceptor inner and outer segment remnants (a) retinal a bridge of photoreceptor remnants (arrow) can still be on day 7 which on day 12 progressing to a hole and the of the hole with increased Optical coherence tomography foveal scans in cases of fovea-off rhegmatogenous retinal detachment demonstrating foveal bacillary layer detachment (BALAD) with hyporeflective cleavage planes (arrowheads) extending from the layer plexiform through the external limiting into the cavity by the In some patients (a and these changes were observed to the location of the junction between the Müller cell cone and at the foveal Optical coherence tomography foveal scans in fovea-off rhegmatogenous retinal detachments demonstrating foveal bacillary layer detachment (BALAD) with significant thinning of the central outer nuclear layer to the BALAD cavity (star), where the central of is In some patients (a and the to be with only a hyperreflective bridge of tissue the foveal In one patient a hyporeflective (arrowhead) was also at the junction of the Müller cell cone and layer at the foveal Optical coherence tomography foveal scans in cases of fovea-off rhegmatogenous retinal detachment demonstrating bacillary layer detachment, lamellar with a residual posterior hyperreflective of photoreceptor inner and outer and cases had residual tissue remnants of reflectivity at the inner of the foveal contiguous with the outer nuclear layer, remnants of the Müller cell Optical coherence tomography foveal scans in cases of fovea-off rhegmatogenous retinal detachment demonstrating bacillary layer detachment with a residual posterior hyperreflective of photoreceptor inner segments and outer segment The of these had retinal layers with a complete absence of the Müller cell cone and central outer nuclear layer. we in the parafoveal outer retina with the morphologic stage of (a) Stage high-frequency and outer retinal (b) Stage 4, loss of of the ORCs with multiple hyperreflective (c) Stage loss of outer retinal observed as moth-eaten appearance of the photoreceptor inner and outer with a residual posterior hyperreflective The residual posterior of the hole and more from to Martins Melo et al. described the morphologic stages of RRD, one of the was the presence of any signs of as defined by the However, development postoperatively may in many detachments, and its earliest particularly those to et al. were the first to the after from eyes with retinal in which the retina not be to RPE despite of Subsequent studies have shown that retinal changes, by leading to of retinal and In a published in Melo et to the earliest OCT associated with with a on the The group identified two distinct with OCT In eyes categorized as with retinal SS-OCT a of changes. The key OCT finding in these patients of ORCs with photoreceptor apposition within and between corrugations, “fused ORCs” and marked retinal thickening [Figure cases demonstrated associated with loss of of the retinal and of the outer retina, extensive structural [Figures and a clinical these were patients had dysregulated or rapidly progressive imaging demonstrating a macula-off rhegmatogenous retinal detachment as retinal and increased the corresponding swept-source optical coherence tomography scans we a bacillary layer with a high of outer retinal corrugations with photoreceptor-photoreceptor apposition within and between corrugations, forming ORCs imaging demonstrating a macula-off rhegmatogenous retinal detachment as retinal fold or the corresponding swept-source optical coherence tomography scans, we retinal changes that from outer retinal corrugations outer retinal corrugations loss of ORC definition with photoreceptor-photoreceptor apposition within and between corrugations, forming ORCs and outer retinal thickening with ORCs ORCs are present in (c) (arrowheads). ORCs may leading to loss of of the outer retinal (white in imaging demonstrating a macula-off rhegmatogenous retinal detachment as retinal the corresponding swept-source optical coherence tomography scans we multiple outer retinal corrugations with photoreceptor-photoreceptor apposition between corrugations indicated by the white is also a component (arrowhead) associated with retinal loss of of the outer and inner retinal (star) and a of the outer retinal the eyes categorized as with subretinal had subretinal hyperreflective on the OCT with associated outer retinal thinning and patchy or complete loss of photoreceptor segments [Figure In a few cases, BALAD and ORFs were observed being by the dense subretinal [Figure patients not present with ORCs on OCT and the corresponding subretinal to from the fundus these patients typically had slowly progressive RRDs, often with an attached posterior imaging demonstrating shallow fovea-involving rhegmatogenous retinal detachment as the corresponding swept-source optical coherence tomography scans we a hyperreflective membrane (arrowheads) from the retinal pigment epithelium along the outer retinal with associated retinal thinning with patchy loss of the bacillary layer and imaging demonstrating shallow fovea-involving rhegmatogenous retinal detachment (RRD) as swept-source optical coherence tomography scans to show a hyperreflective membrane (white arrowheads) along the of the neurosensory retina, in with the of the outer This membrane to along the outer retina, folds of the bacillary layer and leading to a of the outer retinal as observed in higher scans and these OCT that the progression of ORCs and resulting photoreceptor apposition may be associated with retinal to the In their study, Melo et al. early OCT signs of postoperative development in detachments, and they found ORCs at were an independent predictor of postoperative This remained significant even when controlling for as reattachment of retinal detachment, and baseline STAGES OF RETINAL Finally, as the retina undergoes sequential changes during its detachment, it also exhibits stages during et al. evaluated eyes PnR using OCT imaging obtained at following and hourly the reattachment This assessment of retinal reattachment in five Stage 1 of subretinal fluid as the neurosensory retina the Stage 2 is marked by reduction of and of ORCs. In Stage 3, the retina with the followed by Stage 4, characterized by the of the photoreceptor inner and outer Finally, Stage 5 recovery of photoreceptor from the to the EZ the progression through Stage 2 has been associated with postoperative whereas progression through Stage 3 is associated with persistent fluid In OCT has the of RRD by in of the structural and changes that occur in a detachment. OCT from and BALAD to RRD stages with retinal and the of RRD. these imaging allowing not only for more but also for better The use of OCT in the assessment of RRD is a critical more surgical of cases, and of structural and visual outcomes.
Melo et al. (Thu,) studied this question.