Animal models of retinal detachment and reattachment: identifying cellular events that may affect visual recovery

Clinical therapeutics for proliferative vitreoretinopathy in retinal detachment

Proliferative vitreoretinopathy (PVR) is an abnormal and prolonged healing response to retinal injury (retinal detachment, post retinal detachment surgery) characterised by: pre/subretinal membrane formation; retinal gliosis and retinal shortening, retinal pigment epithelium cell proliferation; and increased glial (mainly Mu¨ller cells), fibroblast and inflammatory cell (macrophage, lymphocyte) activity, leading to tractional retinal holes/breaks and multiple costly eye operations suffered by patients. PVR can cause retinal re-detachment following primary surgical intervention for rhegmatogenous retinal detachment. Vitrectomy and scleral buckling surgery are the main approaches for treating PVR complications of retinal detachment. Patients require many operations to remove the scar tissue but vision results are suboptimal, and do not meet patient expectations. Over the past 40 years, this has been one of the greatest challenges for vitreoretinal surgeons and patients. Despite previous large clinical trials of multiple candidate drug therapeutics, no proven adjunctive treatment currently exists to either prevent, reduce, or treat PVR formation in retinal detachment. Both cellular proliferation and the intraocular inflammatory response are realistic targets for adjunctive treatments in PVR. The cellular components of PVR periretinal membranes (retinal pigment epithelial, glial, inflammatory and fibroblastic cells) proliferate and are thus targets for antiproliferative agents. In recent years, several new therapeutics have been tested, and we present an updated review of the clinical therapeutics for PVR in retinal detachment.

Chemically induced cone degeneration in the 13-lined ground squirrel

Animal models of retinal degeneration are critical for understanding disease and testing potential therapies. Inducing degeneration commonly involves the administration of chemicals that kill photoreceptors by disrupting metabolic pathways, signaling pathways, or protein synthesis. While chemically induced degeneration has been demonstrated in a variety of animals (mice, rats, rabbits, felines, 13-lined ground squirrels (13-LGS), pigs, chicks), few studies have used noninvasive high-resolution retinal imaging to monitor the in vivo cellular effects. Here, we used longitudinal scanning light ophthalmoscopy (SLO), optical coherence tomography, and adaptive optics SLO imaging in the euthermic, cone-dominant 13-LGS (46 animals, 52 eyes) to examine retinal structure following intravitreal injections of chemicals, which were previously shown to induce photoreceptor degeneration, throughout the active season of 2019 and 2020. We found that iodoacetic acid induced severe pan-retinal damage in all but one eye, which received the lowest concentration. While sodium nitroprusside successfully induced degeneration of the outer retinal layers, the results were variable, and damage was also observed in 50% of contralateral control eyes. Adenosine triphosphate and tunicamycin induced outer retinal specific damage with varying results, while eyes injected with thapsigargin did not show signs of degeneration. Given the variability of damage we observed, follow-up studies examining the possible physiological origins of this variability are critical. These additional studies should further advance the utility of chemically induced photoreceptor degeneration models in the cone-dominant 13-LGS.

Techniques for subretinal injections in animals

Subretinal injections are not commonly performed during clinical treatment of animals but are frequently used in laboratory animal models to assess therapeutic efficacy and safety of gene and cell therapy products. Veterinary ophthalmologists are often employed to perform the injections in the laboratory animal setting, due to knowledge of comparative ocular anatomy between species and familiarity with operating on non-human eyes. Understanding the different approaches used for subretinal injection in each species and potential complications that may be encountered is vital to achieving successful and reproducible results. This manuscript provides a summary of different approaches to subretinal injections in the most common animal model species, along with information from published literature and experience of the authors to educate novice or experienced surgeons tasked with performing these injections for the first time.

Proliferative vitreoretinopathy: a revised concept of retinal injury and response

Previous concepts for the pathogenesis of proliferative vitreoretinopathy (PVR) have focused on the central role of retinal pigment epithelium cells only, potentially contributing to the lack of clinical advances. More recent studies have demonstrated the essential role of retinal glial cells in the PVR healing response but failed to identify a consistent triggering mechanism.We propose a revised concept for the pathogenesis of PVR based on retinal injury and response. A posterior vitreous detachment (PVD) is invariably present in patients with rhegmatogenous retinal detachment and PVR. There is evidence to suggest that the shearing forces of acute PVD can cause mechanical injury to the inner retina and trigger a subsequent intraretinal glial healing response. That response is characterised by subclinical glial cell activation and proliferation that may then be amplified into full-blown PVR by coexisting pathology such as retinal breaks and detachment.Whether a PVD causes interface pathology depends on the plane of separation of the posterior vitreous and areas of increased vitreoretinal adhesions. If the vitreous separates in a plane or location that damages the inner retina then glial cell activation and proliferation are likely to develop. The severity of the subclinical inner retinal damage may then represent one of the missing links in our understanding of the pathogenesis of PVR and would explain many of the findings we encounter in clinical practice. Controlling the process of acute PVD and subsequent intraretinal response may be essential in the prevention and management of PVR.

Adaptive Optics Flood Illumination Ophthalmoscopy in Nonhuman Primates: Findings in Normal and Short-term Induced Detached Retinae

Objective

To describe adaptive optics flood illumination ophthalmoscopy (AO-FIO) of the photoreceptor layer in normal nonhuman primates (NHPs) and in the case of a short-term induced retinal detachment (RD).

Design

Longitudinal fundamental research study.

Subjects

Four NHPs were used to image normal retinae with AO-FIO (in comparison with 4 healthy humans); 2 NHPs were used to assess the effects of RD.

Intervention

The photoreceptor layer (cone mosaic metrics, including cone density, cone spacing, and cone regularity) was followed with AO-FIO imaging (rtx1, Imagine Eyes) during a surgically induced RD in 2 NHPs using a vehicle solution containing dimethyl sulfoxide, classically used as a chemical solvent. We also performed functional testing of the retina (full-field and multifocal electroretinogram [ERG]).

Main Outcome Measures

Correlation of cone mosaic metrics (cone density, spacing, and regularity) between normal retinae of NHPs and humans, and cone metrics, power spectrum, and ERG wave amplitudes after RD.

Results

Imaging features were very similar in terms of cone reflectivity, cell density, regularity, and spacing values, showing strong positive correlations between NHPs and humans. After RD, AO-FIO revealed several alterations of the cone mosaic slowly recovering during the 3 months after the reattachment, which were not detected functionally by ERG.

Conclusions

These results demonstrate by in vivo AO-FIO imaging the transient structural changes of photoreceptors after an RD in the primate retina. They also provide an interesting illustration of the AO-FIO potential for investigating photoreceptor toxicity during preclinical studies in NHPs with a high translatability to human studies.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Visual loss in surgical retinal disease: retinal imaging and photoreceptor cell counts

Vision loss after detachment of the neurosensory retina is a complex process which is not fully understood. Clinical factors have been identified which contribute to loss of macular function after retinal detachment and laboratory studies have played an important role in understanding the cellular and subcellular pathological processes which underlie the loss of visual function. As clinical imaging has advanced, multiple studies have focused on identifying and correlating clinicopathological features with visual outcomes in patients with rhegmatogenous retinal detachment. Optical coherence tomography, fundus autofluorescence, optical coherence tomography angiography and adaptive optics studies have contributed to the understanding of the anatomical changes in relation to clinical outcomes. A clear understanding of the macular pathology of retinal detachment is fundamental to develop strategies to improve outcomes in patients with rhegmatogenous retinal detachment and analogous retinal diseases where macular neurosensory retinal detachment is part of the pathology. This review assesses the evidence from experimental and pathological studies together with clinical imaging analyses (optical coherence tomography, fundus autofluorescence, optical coherence tomography angiography and adaptive optics) and the contribution of these studies to our understanding of visual outcomes.

Pathophysiology of Secondary Macular Hole in Rhegmatogenous Retinal Detachment

Purpose

To describe the pathophysiology of secondary macular hole (MH) in rhegmatogenous retinal detachment (RRD).

Methods

A retrospective cohort of 360 consecutive primary fovea-off RRDs presenting to St. Michael's Hospital, Toronto, from January 2012 to September 2022 were included. Preoperative OCT was assessed for bacillary layer detachment (BALAD) abnormalities. Histological sections of normal eyes were assessed to inform OCT interpretations. Primary outcome measure was the progression of BALAD to full-thickness MH (FTMH).

Results

Of the 360 patients, 22.5% (n = 81) had BALAD abnormalities at presentation. Eight percent (29/360) had associated MH, of which 79.3% (23/29) were a BALAD-lamellar hole and 20.7% (6/29) were FTMH. After reattachment, 62% of MHs persisted (18/29), of which 83% (15/18) had BALAD-lamellar holes that subsequently progressed to FTMH in a mean of 8.1 ± 3.2 days. BALAD-lamellar holes had significantly worse postoperative visual acuity (P < 0.001) when compared with other BALAD abnormalities (58/81) or with the rest of the cohort (279/360). OCT spectrum from BALAD to FTMH includes (1) cleavage planes extending from Henle fiber layer into the BALAD; (2) central outer nuclear layer thinning; (3) Müller cell cone loss with tissue remnants at the foveal walls; (4) retinal tissue operculum close to BALAD-MH; and (5) progressive thinning or degradation of the posterior band of BALAD-lamellar hole leading to FTMH. Histological specimens identified foveal regions of low mechanical stability.

Conclusions

BALAD plays a crucial role in the pathophysiology of MH in RRDs, which forms owing to sequential changes in four critical areas: RPE-photoreceptor interface, myoid zone, Henle fiber layer, and Müller cell cone with surrounding tissue. Timely management of fovea-off RRD with BALAD may be prudent to avoid the progression to BALAD-lamellar hole, subsequent FTMH, and worse functional outcomes.

Laser-Induced Porcine Model of Experimental Retinal Vein Occlusion: An Optimized Reproducible Approach

Retinal vein occlusion (RVO) is a frequent visually disabling condition. The management of RVO continues to challenge clinicians. Macular edema secondary to RVO is often recurrent, and patients typically require intravitreal injections for several years. Understanding molecular mechanisms in RVO is a key element in improving the treatment of the condition. Studying the molecular mechanisms in RVO at the retinal level is possible using animal models of experimental RVO. Most studies of experimental RVO have been sporadic, using only a few animals per experiment. Here, we report on 10 years of experience of the use of argon laser-induced experimental RVO in 108 porcine eyes from 65 animals, including 65 eyes with experimental branch retinal vein occlusion (BRVO) and 43 eyes with experimental central retinal vein occlusion (CRVO). Reproducibility and methods for evaluating and controlling ischemia in experimental RVO are reviewed. Methods for studying protein changes in RVO are discussed in detail, including proteomic analysis, Western blotting, and immunohistochemistry. Experimental RVO has brought significant insights into molecular changes in RVO. Testing intravitreal interventions in experimental RVO may be a significant step in developing personalized therapeutic approaches for patients with RVO.

Morphologic Stages of Rhegmatogenous Retinal Detachment Assessed Using Swept-Source OCT

PURPOSE

To describe the sequential morphologic changes after rhegmatogenous retinal detachment (RRD) utilizing a novel, objective, and clinically relevant staging system based on swept-source OCT (SS-OCT) and determine its association with the duration of fovea-off and postoperative visual acuity (VA).

DESIGN

Prospective cohort study.

SUBJECTS

Consecutive patients with primary fovea-involving RRD referred to St. Michael's Hospital, Toronto, Canada, from January 2020 to April 2022.

METHODS

All patients underwent SS-OCT and ultrawide-field SS-OCT at baseline. Primary RRDs with breaks above the 8- and 4-o'clock meridians were included. Patients with vision loss for ≥ 3 months, proliferative vitreoretinopathy grade C or worse, a demarcation line, previous vitrectomy, or other retinal pathology were excluded. The staging was based on an assessment of outer retinal morphology on successive SS-OCT scans from the peripheral break to the most posterior aspect of the RRD, following its direction of progression.

MAIN OUTCOME MEASURES

Sequential outer retinal morphologic changes observed using SS-OCT and associated VA at 3 months after surgery.

RESULTS

Forty-nine eyes were included. The mean age (standard deviation [SD]) was 61.2 (15.2) years. The mean presenting logarithm of the minimum angle of resolution (SD) acuity was 1.09 (0.75). All stages observed on a high-definition horizontal 51-line scan were reported. Outer retinal changes occurred in 5 stages: (1) separation of the neurosensory retina from the retinal pigment epithelium (42/49, 85.7%); (2) thickening of inner and outer segments of photoreceptors (45/49, 91.8%); (3) outer retinal corrugation formation: (3a) low-frequency (44/49, 93.6%) and (3b) high-frequency outer retinal corrugations (42/49, 85.7%); (4) loss of the definition of outer retinal corrugations, with concurrent thickening of inner and outer segments (26/49, 53.1%); and (5) patchy (moth-eaten) or complete loss of inner and outer segments (17/49, 34.7%). The mean duration of fovea-off by stage in the parafovea (SD) was 2 (1.4), 2.3 (1.2), 11.4 (8.1), and 12 (13.3) days for stages 3a, 3b, 4, and 5, respectively. There was a statistically significant association between increasing stage of RRD and longer duration of foveal involvement (P = 0.001) and, most importantly, between increasing stage and worse VA at 3 months after surgery (P = 0.011).

CONCLUSIONS

This novel staging system describes the sequential morphologic changes in RRD using SS-OCT. Increasing stage of RRD was associated with worse VA at 3 months after surgery.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Visual Outcomes in Macula-Involving Retinal Detachments Based on Time to Surgical Repair

BACKGROUND AND OBJECTIVE

To examine the relationship between duration of macular detachment and postoperative visual acuity in macula-involving rhegmatogenous retinal detachments.

PATIENTS AND METHODS

Retrospective review of patients who underwent surgical repair of macula-involving rhegmatogenous retinal detachments was conducted with Institutional Review Board approval. Primary outcome measure was postoperative best-corrected visual acuity (BCVA) as dependent on duration of macular detachment.

RESULTS

In eyes with duration of macular detachment less than or equal to 7 days, postoperative BCVA increased by 0.017 logarithm of the minimum angle of resolution (logMAR) units (P = .001), and the odds of achieving logMAR 0 decreased by a factor of 0.43 (95% CI, 0.21 to 0.87; P = .02) with each additional day of detachment. Eyes repaired within 3 days of macular detachment were more likely to have postoperative BCVA of logMAR 0 than eyes repaired 4 to 7 days after macular detachment (odds ratio, 2.32; 95% CI, 1.15 to 4.70; P = .02).

CONCLUSION

Increased duration of macular detachment is associated with progressive decline in postoperative visual acuity. [Ophthalmic Surg Lasers Imaging Retina 2022;53:439-444.].

Changes in circumpapillary retinal nerve fiber layer thickness after vitrectomy for rhegmatogenous retinal detachment

The study aimed to evaluate the long-term changes in circumpapillary retinal nerve fiber layer (RNFL) thickness after vitrectomy for rhegmatogenous retinal detachment (RRD) repair. A total of 33 eyes of 33 patients were enrolled. By using optical coherence tomography, the circumpapillary RNFL thickness was measured before surgery and 1, 3, 6 months and 1, 2, 3 years after surgery and compared with the preoperative value. The effect of duration, location, and extent of RRD on RNFL thickness change was evaluated. There was a significant increase of circumpapillary RNFL thickness at the 1-month, 3-month [except in the nasal superior sector (P = 0.627)], and only in the nasal inferior sector at 6-month (P = 0.010) follow-up compared with the baseline value (all Ps < 0.05). No significant differences were observed 1, 2, and 3 years after the surgery (P > 0.05). The duration, location, and extent of detachment did not reveal significant correlations with RNFL parameters (P > 0.05). Circumpapillary RNFL thickness in eyes with RRD after vitrectomy demonstrated a transient increase during the early postoperative period. This increase was not associated with duration, location, and extent of RRD. At 3 years following surgery, no RNFL thinning or thickening was observed.

Differences in Vascular Density between Detached and Nondetached Areas in Eyes with Rhegmatogenous Retinal Detachment

We examined the vessel density (VD) of the deep capillary plexus (DCP) and choriocapillaris plexus (CCP) by optical coherence tomography (OCT) angiography in eyes with rhegmatogenous retinal detachment, which had similar amounts of detached and nondetached areas in the macula region, and then determined the morphology by OCT until 6 months after surgery. A total of 13 eyes of 13 patients whose average age was 55.8 ± 12.3 years and were successfully treated were enrolled in this study. Throughout the postoperative period, the VD of the DCP in the detached area decreased significantly compared to that in the nondetached area. Conversely, there was no significant difference in the VD of the CCP between the detached and the nondetached areas. The ratio of VD of both the DCP and CCP in the detached area to the in the nondetached area did not show significant changes during the follow-up period of 6 months. The ratio of VD of the DCP in the detached area to that in the nondetached area correlated significantly with the ratio of the external limiting membrane−ellipsoid zone (r = 0.57, p < 0.001) and ellipsoid zone−retinal pigment epithelium (r = 0.39, p < 0.001) thickness in the detached area to that in the nondetached area. A well-preserved DCP blood flow could result in the restoration of the outer retina.

Evaluation of Subretinal fluid Drainage Techniques during Pars Plana Vitrectomy for Primary Rhegmatogenous Retinal Detachment - ELLIPSOID study

PURPOSE

To compare visual acuity and photoreceptor integrity following vitrectomy (PPV) with drainage from the peripheral retinal break(s) (PRB) vs. posterior retinotomy (PR) vs. perfluorocarbon liquid (PFCL) for macula-off rhegmatogenous retinal detachment (RRD).

DESIGN

Retrospective consecutive interventional comparative clinical study.

METHODS

300 consecutive patients (300 eyes) with primary macula-off RRD underwent 23-gauge PPV with SRF drainage through 1) PRB (n=100), 2) PR (n=100), or 3) with PFCL (n=100). Visual acuity and SD-OCT were performed preoperatively and at 3, 6, and 12 months postoperatively. Primary outcomes were visual acuity and discontinuity of the external limiting membrane, ELM; ellipsoid zone, EZ; interdigitation zone, IDZ; and retinal pigment epithelium, RPE at 1-year.

RESULTS

Baseline characteristics were similar. Single-operation reattachment rates were: PRB 86%; PR 85%; PFCL 83%,p=0.9. Mean(±SD) logMAR visual acuity at 1-year was greater with PRB and PR compared to PFCL (PRB=0.6±0.5;PR=0.7±0.6;PFCL=0.9±0.6,p=0.002). There was an association between drainage technique and discontinuity of the ELM (PRB 26%,PR 24%,PFCL 44%,p=0.001), EZ (PRB 29%,PR 31%,PFCL 49%,p<0.001) and IDZ (PRB 43%,PR 39%,PFCL 56%, p=0.004). There was an association between drainage technique and risk of cystoid macular edema (CME) (PRB 28%,PR 39%,PFCL 46%,p=0.003) and ERM (PRB 64%,PR 90%,PFCL 61%,P<0.001).

CONCLUSIONS

PFCL-assisted drainage is associated with worse visual acuity and greater risk of outer retinal band discontinuity and CME compared with PRB or PR. PR had a greater risk of ERM compared with PRB and PFCL. PRB had the best outcomes overall. Drainage technique may impact long-term anatomic and functional outcomes.

Retinal Displacement Following Rhegmatogenous Retinal Detachment: A Systematic Review and Meta-Analysis

Retinal displacement following rhegmatogenous retinal detachment (RRD) repair is an important consideration when assessing the integrity of reattachment, with potential implications on functional outcomes. There are limited data comparing various surgical techniques. We conducted a review of retinal displacement following RRD repair through October 2021, finding twenty-one studies encompassing 1258 unique eyes. Outcome measures included the frequency of retinal displacement, visual acuity, metamorphopsia, and displacement direction. A meta-analysis was performed with data reported as risk ratios or mean difference and 95% confidence intervals. Retinal displacement was found in 35±20% of RRD repairs. Scleral buckle (SB) without tamponade had the lowest rate of retinal displacement (9.60 [2.01-45.95], p=0.005), followed by pneumatic retinopexy (PnR) and finally pars plana vitrectomy (PPV). Silicone oil may reduce risk of displacement following PPV compared to gas (2.16 [1.22-3.83], p=0.009), as may immediate face-down positioning for 2 hours. Retinal displacement following PPV occurred in the downward direction in 92±14% of cases and does not appear to significantly impact visual acuity (0.05 [-0.21-0.31 p=0.70), although it may increase distortion. SB, PnR, PPV with silicone oil, and immediate face-down positioning are likely associated with less retinal displacement. Additional prospective studies are required to increase the certainty of these findings.

Functional and anatomical outcomes after successful repair of macula-off retinal detachment: a 12-month follow-up of the DOREFA study

PURPOSE

To report visual and anatomical outcomes and determine predictors of good visual acuity (VA) recovery after macula-off rhegmatogenous retinal detachment (RD).

METHODS

Prospective multicentre study including 115 eyes from 115 patients successfully operated on for RD, with assessment of VA and spectral-domain optical coherence tomography (SD-OCT) macular images at 1, 3, 6 and 12 months after surgery.

RESULTS

Over the follow-up period, VA significantly improved from median [IQR] 62 [46; 72] ETDRS letters at 1 month to 75 [67; 80] ETDRS letters at 12 months (p < 0.001) with a concomitant decreased number of eyes with any SD-OCT lesions (p < 0.001). The presence of subretinal fluid (SRF) significantly decreased (p < 0.001), as did the number of photoreceptor (PR) layer lesions (p = 0.04). At 12 months, lesions in the PR layer and poor VA recovery were significantly associated with a longer time to surgery (p = 0.007 and p < 0.001, respectively). The rate of patients without PR lesions increased from 40.9% at 1 month to 60.0% at 6 months and 73.9% at 12 months (p < 0.001). The incidence of epiretinal membrane (ERM) significantly increased (p < 0.001), while cystoid macular oedema (CME) remained stable over time. Visual acuity (VA) at 3 months postoperatively was a good reflection of final VA recovery (p < 0.001).

CONCLUSION

Visual acuity (VA) improved in parallel with the decreasing number of eyes with SD-OCT lesions after macula-off rhegmatogenous RD. A long time to surgery was the only preoperative factor associated with poor VA recovery after retinal detachment surgery.

Assessment of Vascular Changes in Patients after Pars Plana Vitrectomy Surgery Due to Macula-Off Rhegmatogenous Retinal Detachment

The aim of this study was to investigate the changes in the retinal capillary plexuses in patients after pars plana vitrectomy (PPV), which is used for the treatment of rhegmatogenous retinal detachment (RRD). In this study, we included the results of 114 patients who underwent PPV after total retinal detachment (RRD; retinal detachment group). It should be kept in mind that to qualify for the study group, there was a condition that retinal detachment be only present in one eye, allowing the fellow healthy eye to be used for the control group, and the study, therefore, did not include cases where retinal detachment occurred binocularly. Optical coherence tomography (OCT) and OCT-A images were taken at 9 ± 2 months (median 10 months) after the surgery, with the study conducted in the years 2017–2019. OCT was used to examine the external limiting membrane (ELM), central macular thickness (CMT) and retinal nerve fiber layer (RNFL), while OCT-angiography (OCT-A) was used to examine the extent of the foveal avascular zone (FAZ) in the deep and superficial capillary plexuses. Changes in the FAZ area of the superficial plexus (SCP) between the study and control groups were analyzed over 346 ± 50 days. In our study, we observed changes in the FAZ area between the RRD and control groups in the SCP (203.65 ± 31.69 μm² vs. 215.30 ± 35.82 μm²; p = 0.28733) and DCP (284.79 ± 35.82 µm² vs. 336.84 ± 32.23 µm²; p = 0.00924). Changes in the RNFL thickness between the study and control groups over 346 ± 50 days were as follows: 90.15 μm vs. 82.44 μm; p = 0.19773. Disruption of the external limiting membrane was observed in 78.95% (90 eyes) of the study group. In the control group, it was undamaged, and no integrity disorder was observed. In the RRD, changes occurred in the FAZ of both the SCP and the DCP, which reduced the extent of this zone, an effect that was more pronounced in DCPs. A better understanding of the anatomical and hemodynamic changes taking place in the retina after macula-off RRD might be helpful in answering the question as to why BCVA in these cases is “only” or “as much as” from 0.4 to 0.1, namely, that it might be related to changes in the neurosensory retina after macular peeling.

Insights into Growth Factors in Liver Carcinogenesis and Regeneration: An Ongoing Debate on Minimizing Cancer Recurrence after Liver Resection

Hepatocellular carcinoma has become a leading cause of cancer-associated mortality throughout the world, and is of great concern. Currently used chemotherapeutic drugs in the treatment of hepatocellular carcinoma lead to severe side effects, thus underscoring the need for further research to develop novel and safer therapies. Liver resection in cancer patients is routinely performed. After partial resection, liver regeneration is a perfectly calibrated response apparently sensed by the body’s required liver function. This process hinges on the effect of several growth factors, among other molecules. However, dysregulation of growth factor signals also leads to growth signaling autonomy and tumor progression, so control of growth factor expression may prevent tumor progression. This review describes the role of some of the main growth factors whose dysregulation promotes liver tumor progression, and are also key in regenerating the remaining liver following resection. We herein summarize and discuss studies focused on partial hepatectomy and liver carcinogenesis, referring to hepatocyte growth factor, insulin-like growth factor, and epidermal growth factor, as well as their suitability as targets in the treatment of hepatocellular carcinoma. Finally, and given that drugs remain one of the mainstay treatment options in liver carcinogenesis, we have reviewed the current pharmacological approaches approved for clinical use or research targeting these factors.

Real-Time In Vivo Assessment of Retinal Reattachment in Humans Using Swept-Source Optical Coherence Tomography

PURPOSE

To assess the in vivo physiology of retinal reattachment in humans using swept-source optical coherence tomography (SS-OCT) in real time.

DESIGN

Prospective case series.

METHODS

Fifteen consecutive patients with fovea-involving rhegmatogenous retinal detachment were undergoing pneumatic retinopexy. SS-OCT was performed at presentation and frequent intervals immediately after pneumatic retinopexy. The primary outcome was longitudinal assessment of early postoperative SS-OCT to establish stages of reattachment.

RESULTS

Most patients (93.3%, 14/15) achieved successful reattachment at the median follow-up duration of 13 weeks (interquartile range 7.5-18.0). Reattachment occurred in 5 specific stages: 1) redistribution of fluid and approach of the neurosensory retina toward the retinal pigment epithelium occurred in 100% (15/15); 2) reduction in cystoid macular edema and improvement of outer retinal corrugations was achieved in 100% (15/15); 3) initial contact of the neurosensory retina to the retinal pigment epithelium occurred completely in 66.7% (10/15); 4) deturgescence of the inner and outer segments of the photoreceptors occurred in 66.7% (10/15); and 5) recovery of photoreceptor integrity occurred in 3 specific substages: 5A) external limiting membrane recovery (10/15, 66.6%); 5B) ellipsoid zone recovery (9/15, 60%); and 5C) interdigitation zone/foveal bulge recovery (3/15, 20%). Twenty percent (3/15) had delayed progression through stage 2, characterized by formation of outer retinal folds. Similarly, 33.3% (5/15) developed residual subfoveal fluid blebs (delayed progression to stage 3).

CONCLUSIONS

This study characterizes the in vivo physiology of retinal reattachment in humans using high-resolution SS-OCT that occurs in 5 specific stages. Delayed progression through certain stages was characterized by postoperative anatomic abnormalities. Am J Ophthalmol 2021;221:•••-•••. © 2021 Elsevier Inc. All rights reserved.

Synaptic Remodeling in the Cone Pathway After Early Postnatal Horizontal Cell Ablation

The first synapse of the visual pathway is formed by photoreceptors, horizontal cells and bipolar cells. While ON bipolar cells invaginate into the photoreceptor terminal and form synaptic triads together with invaginating horizontal cell processes, OFF bipolar cells make flat contacts at the base of the terminal. When horizontal cells are ablated during retina development, no invaginating synapses are formed in rod photoreceptors. However, how cone photoreceptors and their synaptic connections with bipolar cells react to this insult, is unclear so far. To answer this question, we specifically ablated horizontal cells from the developing mouse retina. Following ablation around postnatal day 4 (P4)/P5, cones initially exhibited a normal morphology and formed flat contacts with OFF bipolar cells, but only few invaginating contacts with ON bipolar cells. From P15 on, synaptic remodeling became obvious with clustering of cone terminals and mislocalized cone somata in the OPL. Adult cones (P56) finally displayed highly branched axons with numerous terminals which contained ribbons and vesicular glutamate transporters. Furthermore, type 3a, 3b, and 4 OFF bipolar cell dendrites sprouted into the outer nuclear layer and even expressed glutamate receptors at the base of newly formed cone terminals. These results indicate that cones may be able to form new synapses with OFF bipolar cells in adult mice. In contrast, cone terminals lost their invaginating contacts with ON bipolar cells, highlighting the importance of horizontal cells for synapse maintenance. Taken together, our data demonstrate that early postnatal horizontal cell ablation leads to differential remodeling in the cone pathway: whereas synapses between cones and ON bipolar cells were lost, new putative synapses were established between cones and OFF bipolar cells. These results suggest that synapse formation and maintenance are regulated very differently between flat and invaginating contacts at cone terminals.

The urgency of surgical treatment for rhegmatogenous retinal detachment

The ideal timing of surgery in patients with rhegmatogenous retinal detachment has been discussed for decades. The study situation has improved in recent years so that recommendations can now be made. When the macula is detached, surgical treatment of the retinal detachment should be undertaken within a few days. When the macula is still attached, the near fovea and bullous superotemporal detachment should be classified as an emergency. When planning the operation environmental factors must also be considered, meaning that the performance of the intervention by an experienced surgical team is usually more important for the final result than the retinal condition alone. Influencing factors are discussed in this article and recommendations for dealing with these emergency patients are discussed.

Characteristics of patients with complete visual acuity recovery after vitrectomy for macula-off retinal detachment

PURPOSE

The purpose of this study is to investigate potential factors predicting complete recovery of visual acuity following surgery for macula off retinal detachment (RD).

PATIENTS AND METHODS

Retrospective review of patients operated for macula-off RD at Jules-Gonin Eye Hospital between January 2015 and December 2016. The study included patients with visual acuity recovery of 0 LogMAR. A control group of 83 patients with comparable baseline characteristics but partial recovery of visual acuity after vitrectomy for macula-off RD was used for statistical comparison analysis.

RESULTS

Seventy-four patients, 46 males (62%) and 28 females (38%), were included. Mean age was 65 years (standard deviation: 12). Median follow-up was 6 months (interquartile range: 3). Fifty patients (68%) were pseudophakic. Median pre-op best-corrected visual acuity (BCVA) was 2 LogMAR (interquartile range: 1.22). Forty-three of the patients (58%) had preoperative BCVA equivalent of count fingers or less. The majority of the patients (91%) had up to 3-day duration of macular detachment (MD) before surgery. In comparison only 18% of the group of patients with partial recovery of visual acuity after vitrectomy for macula-off RD had been operated within 3 days of MD (p < 0.0001). In 63% of the 40 cases in whom an optical coherence tomography (OCT) of the fovea could be interpreted, OCT image showed a retained foveal depression of the detached retina, whereas only 35% of the 46 control eyes with adequate OCT imaging showed a retained foveal depression (p = 0.01).

CONCLUSIONS

In our study, patients had significantly better chances of complete visual acuity recovery when operated within 3 days of MD in comparison to more delayed surgery. Additionally, preservation of the foveal depression of the detached retina appeared to be a common characteristic among patients demonstrating complete visual recovery.

Functional and Structural Outcomes at the Foveal Avascular Zone with Optical Coherence Tomography Following Macula off Retinal Detachment Repair

Background

Visual recovery following macula involving rhegmatogenous retinal detachment remains poorly understood. The aim of this work is to correlate the functional and the anatomical changes in retinal vasculature in the foveal avascular zone using optical coherence tomography angiography (OCTA) after successful retinal reattachment repair and correlate this data with retinal thickness and post-operative visual recovery.

Methods

A prospective, comparative observational study of 28 eyes of 14 patients with 14 eyes undergoing macula off retinal detachment repair with pars plana vitrectomy, endo-laser and silicone oil-based tamponade compared with 14 fellow healthy eyes at 1, 6 and 12 weeks post-operative period. The study was conducted at the Research Institute of Ophthalmology, Giza, Egypt between February 2018 and August 2018.

Results

The foveal avascular zone (FAZ) area in the patients group was not significantly different compared to the control group and was found to be negatively correlated with the central retinal thickness in both the study and control group. The superficial capillary plexus (SCP) area at the FAZ was significantly larger than the deep capillary plexus (DCP) area at the FAZ in both the study and control group over the follow-up period. The DCP area at the FAZ was significantly larger at the 3rd follow-up than the 1st follow-up. The SCP FAZ area was significantly larger than the DCP FAZ area in both the study and control group over the follow-up period. BCVA was found to be negatively correlated to the retinal thickness of the temporal 3 mm paracentral quadrant with no correlation with central foveal thickness (CFT) and the FAZ area.

Conclusion

Optical coherence tomography (OCT) and OCTA are valuable noninvasive imaging tools to monitor and predict the structural changes at the foveal avascular zone during the recovery phase after successful retinal reattachment involving macula.

A New Retinal Detachment Treatment Model for Evaluation of Vitreous Tamponades

Purpose: To develop a treatment model of rhegmatogenous retinal detachment (RRD) in which the effects of various vitreous tamponades can be explored. Methods: In a primary session, detachment was produced in the right eye of 24 rabbits using vitrectomy, posterior vitreous detachment, retinal break induction, and subretinal injection of viscoelastic solution. The following day, detachments were treated in 16 eyes using SF6 (n = 8) or Healaflow® (HF, a cross-linked hyaluronic acid hydrogel, n = 8) tamponade. Animals were followed for 1 month and thereafter examined macroscopically and morphologically in hematoxylin and eosin-stained sections. Results: Retinal detachment (RD) was successfully treated using repeated surgery. Two HF eyes developed progressive vitritis and were excluded from further evaluation. Enlargement of the initial retinal rupture with concomitant RD was seen in 4/8 SF6 eyes, while all 6 HF eyes displayed an attached retina. Attached areas showed a normal retinal morphology except for in 1 HF eye with extensive degeneration. Conclusions: The RRD repeat vitrectomy model offers a possibility to explore the efficacy and complications of novel potential vitreous tamponades. Gel-based Healaflow® displays excellent anatomic reattachment, however, vitritis and retinal degeneration in some cases warrants further investigation.

Inter- and Intra-individual Variations in Foveal Outer Nuclear Layer Thickness and Their Associations with Clinical Characteristics in a Healthy Chinese Population

Purpose

To evaluate foveal outer nuclear layer (ONL) thickness and the difference thereof between bilateral eyes and their possible associations with clinical characteristics in a healthy Chinese population.

Materials and Methods

Normal subjects were enrolled. Generalized linear models were used to assess the associations of foveal ONL thickness with sex, age, and spherical equivalents (SEs) and the associations of the difference in foveal ONL thickness between bilateral eyes with sex, age, and difference in SEs between bilateral eyes.

Results

Totally, 304 subjects were included. The average foveal ONL thickness was 103.19 ± 14.25 (range 70-151) μm in the right eye and 103.90 ± 14.63 (range 69-155) μm in the left eye. The mean difference in foveal ONL thickness between right and left eyes was -0.71 ± 4.36 (range -13 to +12) μm. Men had slightly greater foveal ONL thickness values in both right and left eyes compared with women (both P < 0.05); however, some women had a thicker foveal ONL than that of men (85/198 vs. 46/106 in the right eye; 79/198 vs. 52/106in the left eye). Age and SEs were not associated with foveal ONL thickness in either eye (all P > 0.05). Sex, age, and difference in SEs between bilateral eyes were not associated with the difference in foveal ONL thickness between bilateral eyes (all P > 0.05).

Conclusions

Foveal ONL thickness showed wide variation in a normal Chinese population but little difference between bilateral eyes. Both these parameters could not be adjusted by sex, age, SEs, or the SEs difference between bilateral eyes. Thus, in those diseases involving only one eye, the difference or ratio of foveal ONL thickness between the affected eye and normal fellow eye may reflect the actual degree of the disease, rather than the foveal ONL thickness in the affected eye alone.

Loss of retinal tension and permanent decrease in retinal function: a new porcine model of rhegmatogenous retinal detachment

PURPOSE

Permanent loss of visual function after rhegmatogenous retinal detachment can occur despite successful surgical reattachment in humans. New treatment modalities could be explored in a detachment model with loss of retinal function. In previous porcine models, retinal function has returned after reattachment, regardless of height and duration of detachment. Difference in retinal tension between the models and the disease might explain these different outcomes. This study investigates, for the first time in an in vivo porcine model, another characteristic of rhegmatogenous retinal detachment - the loss of retinal tension.

METHODS

Left eyes (n = 12) of 3-month-old domestic pigs were included. Baseline multifocal electroretinogram (mfERG) and a fundus photograph were obtained following anaesthesia (isoflurane). The pigs were vitrectomized, saline was injected subretinally, and the RPE was removed. The eyes were evaluated at 2, 4 and 6 weeks after surgery. Four eyes were enucleated at each evaluation for histologic examinations.

RESULTS

A retinal detachment structurally resembling rhegmatogenous retinal detachment was induced in 11 out of 12 pigs. MfERG amplitudes were significantly decreased despite partial reattachment four and 6 weeks after detachment. The retinal thickness decreased with 27%, the inner nuclear layer degenerated, Müller cells hypertrophied, and outer segments were lost. In the ganglion cell layer, cellularity increased and there was cytoplasmic staining with Cyclin D1. Vimentin and GFAP staining for glial cells increased. After 2 weeks of detachment, the ganglion cells had lost their nucleus and nucleolus.

CONCLUSIONS

Loss of retinal tension in the detached retina seems to induce permanent damage with loss of retinal function. Death of ganglion cells, observed as soon as 2 weeks after detachment, explains the permanent loss of retinal function. The new model enables investigations of time-relationship between retinal detachment and lasting damage in addition to exploration of novel treatment modalities.

Subretinal surgery: functional and histological consequences of entry into the subretinal space

BACKGROUND AND OBJECTIVES

Gene-therapy, stem-cell transplantation and surgical robots hold the potential for treatment of currently untreatable retinal degenerative diseases. All of the techniques require entry into the subretinal space, which is a potential space located between the retina and the retinal pigment epithelium (RPE). Knowledge about obstacles and critical steps in relation to subretinal procedures is therefore needed. This thesis explores the functional and histological consequences of separation of the retina from the RPE, extensive RPE damage, a large cut in the retina (retinotomy) and RPE phagocytosis in a porcine model.

METHODS

Experiments were performed in 106 female domestic pigs of Danish landrace distributed over five studies. Under general anesthesia, different procedures for expansion of the subretinal space were conducted. Outcomes were visual function measured electrophysiologically with multifocal electroretinogram (mfERG) and retinal morphology examined histologically. Study I: The effect of anesthesia on mfERG was examined by repeated recordings for 3 hr in isoflurane or propofol anesthesia. Outcome was mfERG amplitude. Study II: Consequences of a large separation of the photoreceptors from the RPE were examined by injecting a perfluorocarbon-liquid (decalin) into the subretinal space. Two weeks after, in a second surgery, decalin was withdrawn. Outcomes were mfERG and histology 4 weeks after decalin injection. Study III: Extensive RPE damage was examined by expanding the subretinal space with saline and removing large sheets of RPE-cells through a retinotomy. Outcomes were mfERG and histology 2, 4 and 6 weeks after the procedure. Study IV: Consequences of a large retinotomy were examined by similar procedures as in Study III, but in study IV only a few RPE cells were removed. Outcomes were mfERG and histology 2 and 6 weeks after surgery. Study V: Clearance of the subretinal space was examined by injecting fluorescent latex beads of various sizes into the subretinal space. Outcome was histologic location of the beads at different time intervals after the procedure.

RESULTS

Study I: MfERG amplitudes decreased linearly as a function of time in propofol or isoflurane anesthesia. Duration of mfERG recording could be decreased without compromising quality, and thereby could time in anesthesia be reduced. Study II: MfERG and histology remained normal after reattachment of a large and 2-week long separation of the photoreceptors and RPE. Repeated entry into the subretinal space was well tolerated. Fluid injection into the subretinal space constitutes a risk of RPE-damage. Study III: Removal of large sheets of retinal pigment epithelial cells triggered a widespread rhegmatogenous-like retinal detachment resulting in visual loss. Study IV: A large retinotomy with limited damage of the RPE was well tolerated, and visual function was preserved. Study V: Subretinal latex beads up to 4 μm were phagocytosed by the RPE and passed into the sub-RPE space. Beads up to 2 μm travelled further through the Bruch's membrane and were found in the choroid, sclera and inside blood vessels.

CONCLUSION

A large expansion of the subretinal space, repeated entry, a large retinotomy and limited RPE damage is well tolerated and retinal function is preserved. Subretinal injection of fluid can damage the RPE and extensive RPE damage can induce a rhegmatogenous-like retinal detachment with loss of visual function. Foreign substances exit the subretinal space and can reach the systemic circulation.

Actin Dynamics, Regulated by RhoA-LIMK-Cofilin Signaling, Mediates Rod Photoreceptor Axonal Retraction After Retinal Injury

Purpose

Retraction of the axon terminals of rod photoreceptors after retinal detachment breaks the first synapse in the visual pathway, resulting in visual impairment. Previous work showed that the mechanism of axonal retraction involves RhoA signaling and its downstream effector LIM Kinase (LIMK) activation. We examined the response of the downstream component cofilin, a direct binding protein of actin filaments, as well as the regulation by RhoA-LIMK-Cofilin signaling of actin assembly/disassembly, in the presynaptic ribbon terminal of injured rod cells.

Methods

Injury was produced by retinal detachment or rod cell isolation. Detached porcine retina was probed for levels and localization of phosphorylated cofilin with Western blots and confocal microscopy, whereas rod cell cultures of dissociated salamander retina were examined for filamentous actin assembly/disassembly with a barbed end assay and phalloidin staining.

Results

A detachment increased phosphorylation of cofilin in retinal explants; phosphorylation occurred in rod terminals in sections of detached retina. Isolation of rod cells resulted in axon retraction accompanied by an increase in actin barbed ends and a decrease in net filament labeling. All changes were significantly reduced by either Rho kinase (ROCK) or LIMK inhibition, using Y27632 or BMS-5, respectively. Cytochalasin D also reduced retraction and stabilized filaments in isolated rod cells.

Conclusions

These results indicate that actin depolymerization via activation of RhoA downstream kinases and cofilin contributes to axon retraction. Preventing depolymerization, in addition to actomyosin contraction, may stabilize ribbon synapses after trauma.

Prevalence and risk factors for outer retinal layer damage after macula-off retinal detachment

PURPOSE

To report the prevalence of outer retinal layer (ORL) damage after macula-off rhegmatogenous retinal detachment (RRD) surgery and to determine its associated preoperative risk factors.

METHODS

253 eyes successfully operated for macula-off RRD were included in the study. The integrity of the external limiting membrane (ELM), ellipsoid zone (EZ) and cone interdigitation zone (CIZ) of the photoreceptors was assessed at 1 month and 6 months using spectral-domain optical coherence tomography. Risk factors were analysed using univariate and multivariate logistic regression. The correlation between ORL integrity and visual outcomes was also evaluated.

RESULTS

CIZ, EZ and ELM defects were found in, respectively, 198 (93.4%) eyes, 100 (47.2%) eyes, 64 (30.2%) eyes at 1 month and in 160 (63.2%) eyes, 44 (17.4%) eyes and 18 (7.1%) eyes at 6 months. In multivariate analysis, duration of macular detachment was the only factor associated with ORL damage at 6 months (p=0.007). Best-corrected visual acuity significantly improved from 0.5±0.3 at 1 month to 0.3±0.3 logarithm of minimal angle of resolution at 6 months (p<0.001) and was strongly correlated with the number of affected bands (p<0.001).

CONCLUSION

Prevalence of outer retinal band defects substantially decreased through the study period, confirming the ability of photoreceptors to recover over time. However, shorter interval to surgery and better visual outcomes were significantly associated with fewer defects within the ORL at 6 months. These findings suggest that earlier surgery may limit RRD-associated photoreceptor degeneration and improve the patient's visual prognosis.

Retinal Nerve Fiber Layer Changes Following Primary Retinal Detachment Repair with Silicone Oil Tamponade and Subsequent Oil Removal

Purpose:

To evaluate the correlation between the retinal nerve fiber layer (RNFL), particularly the temporal RNFL (TRNFL), and visual outcomes following surgery for rhegmatogenous retinal detachment (RRD).

Methods:

This retrospective study was performed at a tertiary center; 32 patients underwent single and successful vitrectomy for total RRD using silicone oil as tamponade. Data were collected after oil removal. RNFL thickness and central foveal thickness (CFT) were measured using spectral domain optical coherence tomography. RNFL thickness and CFT of normal eyes were acquired as a control to calculate percentage changes in the affected eyes. The correlation between postoperative best-corrected visual acuity (BCVA) and TRNFL changes was the primary outcome measure.

Results:

Postoperative BCVA correlated negatively with retinal detachment (RD) duration (Pearson coefficient 0.56, P = 0.001) and percentage loss in TRNFL thickness (Pearson Coefficient 0.41, P = 0.02). The macula lost the maximum RNFL thickness (26%). The mean percentage loss of TRNFL was significantly higher in patients with postoperative BCVA <6/60 (42.63% vs. 24.06%, P = 0.009). Patients with postoperative BCVA <6/60 had a significantly longer mean RD duration (29 days) than those with postoperative BCVA >6/60 (17.5 days) (P = 0.026).

Conclusion:

When eyes with RRD are successfully repaired using silicone oil tamponade, the thickness of the RNFL decreases, particularly in the macula, and less macular neuronal loss is associated with better visual outcomes.

Inflammation-Induced Photoreceptor Cell Death

Neuroinflammation is an important aspect of many diseases of the eye, and experimental animal models have been widely used to determine its impact on retinal homeostasis and neuron survival. Physical separation of the neurosensory retina from the underlying retinal pigment epithelium (RPE) results in activation and infiltration of macrophages. Numerous studies have shown the critical role of macrophages in retinal disease processes. In retinal detachment, accumulation of macrophages in the subretinal space is associated with changes in cytokine and chemokine profile which lead to photoreceptor cell death. Targeted disruption of macrophage chemotaxis significantly reduces retinal detachment-induced photoreceptor degeneration. Apoptosis is the predominant mechanism of cell death; however regulated necrosis is also a contributor of photoreceptor loss. Therefore, effective neuroprotective approaches could integrate combined inhibition of both apoptotic and regulated necrosis pathways.

The chick eye in vision research: An excellent model for the study of ocular disease

The domestic chicken, Gallus gallus, serves as an excellent model for the study of a wide range of ocular diseases and conditions. The purpose of this manuscript is to outline some anatomic, physiologic, and genetic features of this organism as a robust animal model for vision research, particularly for modeling human retinal disease. Advantages include a sequenced genome, a large eye, relative ease of handling and maintenance, and ready availability. Relevant similarities and differences to humans are highlighted for ocular structures as well as for general physiologic processes. Current research applications for various ocular diseases and conditions, including ocular imaging with spectral domain optical coherence tomography, are discussed. Several genetic and non-genetic ocular disease models are outlined, including for pathologic myopia, keratoconus, glaucoma, retinal detachment, retinal degeneration, ocular albinism, and ocular tumors. Finally, the use of stem cell technology to study the repair of damaged tissues in the chick eye is discussed. Overall, the chick model provides opportunities for high-throughput translational studies to more effectively prevent or treat blinding ocular diseases.

RhoA Signaling and Synaptic Damage Occur Within Hours in a Live Pig Model of CNS Injury, Retinal Detachment

PURPOSE

The RhoA pathway is activated after retinal injury. However, the time of onset and consequences of activation are unknown in vivo. Based on in vitro studies we focused on a period 2 hours after retinal detachment, in pig, an animal whose retina is holangiotic and contains cones.

METHODS

Under anesthesia, retinal detachments were created by subretinal injection of a balanced salt solution. Two hours later, animals were sacrificed and enucleated for GTPase activity assays and quantitative Western blot and confocal microscopy analyses.

RESULTS

RhoA activity with detachment was increased 1.5-fold compared to that in normal eyes or in eyes that had undergone vitrectomy only. Increased phosphorylation of myosin light chain, a RhoA effector, also occurred. By 2 hours, rod cells had retracted their terminals toward their cell bodies, disrupting the photoreceptor-to-bipolar synapse and producing significant numbers of spherules with SV2 immunolabel in the outer nuclear layer of the retina. In eyes with detachment, distant retina that remained attached also showed significant increases in RhoA activity and synaptic disjunction. Increases in RAC1 activity and glial fibrillary acidic protein (GFAP) were not specific for detachment, and sprouting of bipolar dendrites, reported for longer detachments, was not seen. The RhoA kinase inhibitor Y27632 significantly reduced axonal retraction by rod cells.

CONCLUSIONS

Activation of the RhoA pathway occurs quickly after injury and promotes synaptic damage that can be controlled by RhoA kinase inhibition. We suggest that retinal detachment joins the list of central nervous system injuries, such as stroke and spinal cord injury, that should be considered for rapid therapeutic intervention.

Regeneration of Photoreceptor Outer Segments After Scleral Buckling Surgery for Rhegmatogenous Retinal Detachment

PURPOSE

To investigate the regeneration of the cone outer segments in eyes after surgery for fovea-off rhegmatogenous retinal detachment with an adaptive optics (AO) fundus camera and to correlate these findings with the findings of optical coherence tomography (OCT).

DESIGN

Retrospective, observational case series.

METHODS

Medical charts of 21 eyes of 21 patients who had undergone surgery for fovea-off rhegmatogenous retinal detachment were retrospectively studied. Cone mosaic images were obtained with an AO fundus camera. Cone packing density at 2 degrees from the fovea within the previously detached area was measured 6 and 12 months after surgery. Retinal thicknesses between the interdigitation zone and the retinal pigment epithelium (IZ-RPE) and between the ellipsoid zone and the retinal pigment epithelium (EZ-RPE) were measured in OCT images.

RESULTS

Cone density 12 months after surgery was significantly increased from that at 6 months (P = .001), but was still significantly lower than that of normal fellow eyes (P < .001). IZ-RPE and EZ-RPE thickness significantly increased from 6 to 12 months (P = .045, P = .033, respectively), and these values were not significantly different from those of normal fellow eyes. Multivariate analysis showed that cone density at 12 months was significantly associated with IZ-RPE thickness (P = .002), and increases in cone packing density were significantly associated with increases in IZ-RPE thickness (P = .001).

CONCLUSIONS

Recovery of cone packing density measured by AO was associated with structural recovery of the outer retina observed in OCT, suggesting regeneration of the photoreceptor outer segment after surgery.

LONGITUDINAL QUANTITATIVE EVALUATION OF PHOTORECEPTOR VOLUME FOLLOWING REPAIR OF MACULA-OFF RETINAL DETACHMENT

PURPOSE

To quantify photoreceptor volume changes after successful surgical repair of macula-off retinal detachment and to correlate these volumetric changes to postoperative best-corrected visual acuity (BCVA).

METHODS

Retrospective study of 15 eyes of 15 patients with macula-off retinal detachment who underwent successful surgical repair. A minimum of 4 optical coherence tomography scans that straddled the foveal center was used to quantify the central photoreceptor volume (central 1 mm).

RESULTS

Mean photoreceptor volume at the first postoperative visit was 0.451 mm, increasing to 0.523 mm at the final postoperative visit (P = 0.004). Mean BCVA improved from 1.13 ± 0.59 logarithm of the minimum angle of resolution units (∼20/270) preoperatively to 0.52 ± 0.42 logarithm of the minimum angle of resolution units (∼20/66) at the final postoperative visit (P = 0.001). Mean photoreceptor volume at either the initial or final visit demonstrated significant correlations with final postoperative BCVA (r = -0.670, P = 0.017 and r = -0.753, P = 0.005, respectively). Shorter time interval from diagnosis to surgery was significantly associated with greater mean final postoperative photoreceptor volume (r = -0.588, P = 0.021) and better mean final postoperative BCVA (r = 0.709, P = 0.003).

CONCLUSION

We observed a significant increase in photoreceptor volume after successful retinal detachment repair; photoreceptor volume was positively associated with BCVA and time to surgery. Our series emphasizes the importance of prompt surgical repair and shows that photoreceptor recovery and volumetric improvement correlate significantly with BCVA.

Outer Plexiform Layer Structures Are Not Altered Following AAV-Mediated Gene Transfer in Healthy Rat Retina

Ocular gene therapy approaches have been developed for a variety of different diseases. In particular, clinical gene therapy trials for RPE65 mutations, X-linked retinoschisis, and choroideremia have been conducted at different centers in recent years, showing that adeno-associated virus (AAV)-mediated gene therapy is safe, but limitations exist as to the therapeutic benefit and long-term duration of the treatment. The technique of vector delivery to retinal cells relies on subretinal injection of the vector solution, causing a transient retinal detachment. Although retinal detachments are known to cause remodeling of retinal neuronal structures as well as significant cell loss, the possible effects of this short-term therapeutic retinal detachment on retinal structure and circuitry have not yet been studied in detail. In this study, retinal morphology and apoptotic status were examined in healthy rat retinas following AAV-mediated gene transfer via subretinal injection with AAV2/5.CMV.d2GFP or sham injection with fluorescein. Outer plexiform layer (OPL) morphology was assessed by immunohistochemical labeling, laser scanning confocal microscopy, and electron microscopy. The number of synaptic contacts in the OPL was quantified after labeling with structural markers. To assess the apoptotic status, inflammatory and pro-apoptotic markers were tested and TUNEL assay for the detection of apoptotic nuclei was performed. Pre- and postsynaptic structures in the OPL, such as synaptic ribbons or horizontal and bipolar cell processes, did not differ in size or shape in injected versus non-injected areas and control retinas. Absolute numbers of synaptic ribbons were not altered. No signs of relevant gliosis were detected. TUNEL labeling of retinal cells did not vary between injected and non-injected areas, and apoptosis-inducing factor was not delocalized to the nucleus in transduced areas. The neuronal circuits in the OPL of healthy rat retinas undergoing AAV-mediated gene transfer were not altered by the temporary retinal detachment caused by subretinal injection, the presence of viral particles, or the expression of green fluorescent protein as a transgene. This observation likely requires further investigations in the dog model for RPE65 deficiency in order to determine the impact of RPE65 transgene expression on diseased retinas in animals and men.

Lim kinase, a bi-functional effector in injury-induced structural plasticity of synapses

The structural plasticity of synaptic terminals contributes to normal nervous system function but also to neural degeneration, in the form of terminal retraction, and regeneration, due to process growth. Synaptic morphological change is mediated through the actin cytoskeleton, which is enriched in axonal and dendritic terminals. Whereas the three RhoGTPases, RhoA, Cdc42 and Rac, function as upstream signaling nodes sensitive to extracellular stimuli, LIMK-cofilin activity serves as a common downstream effector to up-regulate actin turnover, which is necessary for both polymerization and depolymerization. The dual effects of LIMK activity make LIMK a potential target of therapeutic intervention for injury-induced synaptic plasticity, as LIMK inhibition can stabilize actin cytoskeleton and preserve existing structure. This therapeutic benefit of LIMK inhibition has been demonstrated in animal models of injury-induced axon retraction and neuritic sprouting by rod photoreceptors. A better understanding of the regulation of LIMK-cofilin activity and the interaction with the microtubular cytoskeleton may open new ways to promote synaptic regeneration that can benefit neuronal degenerative disease.

LIM Kinase, a Newly Identified Regulator of Presynaptic Remodeling by Rod Photoreceptors After Injury

PURPOSE

Rod photoreceptors retract their axon terminals and develop neuritic sprouts in response to retinal detachment and reattachment, respectively. This study examines the role of LIM kinase (LIMK), a component of RhoA and Rac pathways, in the presynaptic structural remodeling of rod photoreceptors.

METHODS

Phosphorylated LIMK (p-LIMK), the active form of LIMK, was examined in salamander retina with Western blot and confocal microscopy. Axon length within the first 7 hours and process growth after 3 days of culture were assessed in isolated rod photoreceptors treated with inhibitors of upstream regulators ROCK and p21-activated kinase (Pak) (Y27632 and IPA-3) and a direct LIMK inhibitor (BMS-5). Porcine retinal explants were also treated with BMS-5 and analyzed 24 hours after detachment. Because Ca2+ influx contributes to axonal retraction, L-type channels were blocked in some experiments with nicardipine.

RESULTS

Phosphorylated LIMK is present in rod terminals during retraction and in newly formed processes. Axonal retraction over 7 hours was significantly reduced by inhibition of LIMK or its regulators, ROCK and Pak. Process growth was reduced by LIMK or Pak inhibition especially at the basal (axon-bearing) region of the rod cells. Combining Ca2+ channel and LIMK inhibition had no additional effect on retraction but did further inhibit sprouting after 3 days. In detached porcine retina, LIMK inhibition reduced rod axonal retraction and improved retinal morphology.

CONCLUSIONS

Thus structural remodeling, in the form of either axonal retraction or neuritic growth, requires LIMK activity. LIM kinase inhibition may have therapeutic potential for reducing pathologic rod terminal plasticity after retinal injury.

Foveal Structure in Macula-off Rhegmatogenous Retinal Detachment after Scleral Buckling or Vitrectomy

PURPOSE

To evaluate foveal microstructural changes and to determine its association with visual outcomes after reattachment of rhegmatogenous retinal detachments (RRDs) by scleral buckling (SB) or pars plana vitrectomy (PPV).

METHODS

Using spectral domain optical coherence tomography (SD-OCT), foveal microstructure in eyes with macula-off RRD were studied 1, 3, 6, 9, 12 and 15 months after PPV or SB and correlated with visual outcomes.

RESULTS

Forty-two eyes were included in the final analysis. Even with improved microstructural changes and normalization of retinal structures on OCT, final visual acuity was not correlated with microstructural changes in eyes undergoing PPV. In the SB group, final visual acuity was significantly correlated with an intact inner segment/outer segment (IS/OS) junction (P = 0.013). There was no significant correlation between final visual acuity and presence of subretinal fluid (SRF) in either group.

CONCLUSION

After SB, eyes with an intact IS/OS junction had better final visual acuity. In the PPV group, there was no significant correlation between microstructural changes and visual acuity. The presence of SRF did not influence final visual acuity in both groups.

Activation of glucocorticoid receptors in Müller glia is protective to retinal neurons and suppresses microglial reactivity

Reactive microglia and macrophages are prevalent in damaged retinas. Glucocorticoid signaling is known to suppress inflammation and the reactivity of microglia and macrophages. In the vertebrate retina, the glucocorticoid receptor (GCR) is known to be activated and localized to the nuclei of Müller glia (Gallina et al., 2014). Accordingly, we investigated how signaling through GCR influences the survival of neurons using the chick retina in vivo as a model system. We applied intraocular injections of GCR agonist or antagonist, assessed microglial reactivity, and the survival of retinal neurons following different damage paradigms. Microglial reactivity was increased in retinas from eyes that were injected with vehicle, and this reactivity was decreased by GCR-agonist dexamethasone (Dex) and increased by GCR-antagonist RU486. We found that activation of GCR suppresses the reactivity of microglia and inhibited the loss of retinal neurons resulting from excitotoxicity. We provide evidence that the protection-promoting effects of Dex were maintained when the microglia were selectively ablated. Similarly, intraocular injections of Dex protected ganglion cells from colchicine-treatment and protected photoreceptors from damage caused by retinal detachment. We conclude that activation of GCR promotes the survival of ganglion cells in colchicine-damaged retinas, promotes the survival of amacrine and bipolar cells in excitotoxin-damaged retinas, and promotes the survival of photoreceptors in detached retinas. We propose that suppression of microglial reactivity is secondary to activation of GCR in Müller glia, and this mode of signaling is an effective means to lessen the damage and vision loss resulting from different types of retinal damage.

Analytical platforms in vitreoretinal proteomics

Current proteomic technologies can effectively be used to study the proteins of the vitreous body and retina in health and disease. The use of appropriate samples, analytical platform and bioinformatic method are essential factors to consider when undertaking such studies. Certain proteins may hinder the detection and evaluation of more relevant proteins associated with pathological processes if not carefully considered, particularly in the sample preparation and data analysis stages. The utilization of more than one quantification technique and database search program to expand the level of proteome coverage and analysis will help to generate more robust and worthwhile results. This review discusses important aspects of sample processing and the use of label and label-free quantitative proteomics strategies applied to the vitreous and retina.

Improvement and decline in vision with gene therapy in childhood blindness

Retinal gene therapy for Leber's congenital amaurosis, an autosomal recessive childhood blindness, has been widely considered to be safe and efficacious. Three years after therapy, improvement in vision was maintained, but the rate of loss of photoreceptors in the treated retina was the same as that in the untreated retina. Here we describe long-term follow-up data from three treated patients. Topographic maps of visual sensitivity in treated regions, nearly 6 years after therapy for two of the patients and 4.5 years after therapy for the third patient, indicate progressive diminution of the areas of improved vision. (Funded by the National Eye Institute; ClinicalTrials.gov number, NCT00481546.).

Dye-Free Porcine Model of Experimental Branch Retinal Vein Occlusion: A Suitable Approach for Retinal Proteomics

Branch retinal vein occlusion induces complex biological processes in the retina that are generated by a multitude of interacting proteins. These proteins and their posttranslational modifications can effectively be studied using modern proteomic techniques. However, no method for studying large-scale protein changes following branch retinal vein occlusion has been available until now. Obtainment of retinal tissue exposed to branch retinal vein occlusion is only available through experimental animal models. Traditional models of experimental branch retinal vein occlusion require the use of Rose Bengal dye combined with argon laser photocoagulation. The use of Rose Bengal dye is problematic in proteomic studies as the dye can induce multiple protein modifications when irradiated. This paper presents a novel technique for proteomic analysis of porcine retinal tissue with branch retinal vein occlusion combining a dye-free experimental model with label-free liquid chromatography mass spectrometry based proteomics.

Correlation of preoperative retinal pigment epithelium status with foveal microstructure in repaired macular holes

PURPOSE

To investigate, with spectral-domain optical coherence tomography, if the preoperative status of the retinal pigment epithelium (RPE) affects the postoperative foveal morphology and visual outcomes in eyes with surgically closed macular holes (MHs).

METHODS

In 52 eyes with surgically closed MHs, preoperative RPE morphology was evaluated and graded based on the measurement of the largest hyperreflective protrusions above the RPE line. Foveal microstructural features and best-corrected visual acuity (BCVA) were evaluated 12 months after surgery.

RESULTS

At 12 months, a significant correlation was found between postoperative degree of integrity of the photoreceptors with preoperative RPE morphology, and base diameter of the hole (p = 0.003 and p = 0.028, respectively); mean BCVA at 12 months in eyes with diffuse RPE alteration was significantly lower than in eyes with small or no RPE alteration (p < 0.05).

CONCLUSIONS

Preoperative RPE integrity may be indicative of good photoreceptor restoration and visual recovery in patients with surgically closed MHs.