Functional recovery after experimental RPE debridement, mfERG studies in a porcine model

Retinal pigment epithelial responses based on the irradiation density of selective retina therapy

PURPOSE

We evaluated the response of the retinal pigment epithelium (RPE) to high-density (HD) or low-density (LD)-selective retina therapy (SRT) with real-time feedback-controlled dosimetry (RFD) in rabbits.

METHODS

Sixteen eyes of 8 Chinchilla Bastard rabbits underwent SRT with RFD (527-nm wavelength, 1.7-μs pulse duration), using automatically titrated pulse energy, by using optoacoustic dosimetry or real-time reflectometry. Fifty-six 25-μJ SRT, including LD-SRT (1-spot or 2-spot-spacing) and HD-SRT (4-spot, 7-spot, or 9-spot-no-spacing), were applied per eye. Color fundus photography and fundus fluorescein angiography (FFA) were used to confirm SRT spots 1-h post-SRT. Light microscopy and scanning electron microscopy (SEM) were performed at 2-h, 3-day, 7-day, and 1-month post-treatment.

RESULTS

We tested 896 spots irradiated by SRT with RFD and confirmed that SRT lesions were adequate, based on invisibility on fundoscopy and visibility on FFA. On SEM, at 2-h post-SRT, flattened RPE cells were observed in the center of the SRT lesion. While normal RPE cells were clearly observed between LD-SRT lesions, healthy RPE cells were rare in HD-SRT lesions at 2-h post-treatment. At 7-day post-SRT, SEM revealed completely restored LD-SRT lesions with small or large RPE cells with microvilli, whereas HD-SRT lesions were covered with RPE cells without microvilli. At 1-month post-SRT, SEM revealed restored RPE cells with microvilli in HD-SRT lesions. On light microscopy, both HD- and LD-SRT lesions were completely restored with adjacent RPE cells and spared photoreceptors at 1-month post-treatment.

CONCLUSIONS

Although both HD- and LD-SRT lesions had recovered at 1-month post-SRT, LD-SRT lesions healed faster than HD-SRT lesions.

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.

Bruch's membrane allows unhindered passage of up to 2 μm latex beads in an in vivo porcine model

PURPOSE

It has been proposed that changes in the permeability of Bruch's membrane play a role in the pathogenesis of age-related macular degeneration (AMD). This paper investigates, in an in vivo porcine model, the migration of fluorescent latex beads across the Bruch's membrane after subretinal injection.

METHODS

Forty-one healthy eyes of 33 three-month-old domestic pigs received a subretinal injection of 0.5, 1.0, 2.0, or 4.0 μm fluorescent latex beads. Between three hours and five weeks after injection evaluations were performed with fundus photographs and histology. Fluorescent beads were identified in unstained histologic sections using the rhodamine filter with the light microscope.

RESULTS

The fluorescent latex beads relocated from the subretinal space. Intact beads up to 2.0 μm were found in the choroid, sclera, and extrascleral space. The smaller beads were also found inside choroidal and extrascleral blood vessels. In contrast, the larger beads of 4.0 μm did not pass the Bruch's membrane.

CONCLUSION

Subretinally implanted beads up to 2.0 μm pass the Bruch's membrane intact and cross the blood-ocular barrier. The intact beads are found in the choroid, sclera and inside blood vessels. The results give reason to consider the role of subretinal clearance and passage of Bruch's membrane in the development of AMD.

The retina of the collared peccary (Pecari tajacu): structure and function

OBJECTIVE

To study retinal morphology and function in the collared peccary, an ungulate species distantly related to the domestic pig.

ANIMAL STUDIES

Twenty captive peccaries anesthetized for routine health examinations. Procedures No abnormalities were noted on a complete ophthalmic examination. Fundi were examined ophthalmoscopically and photographed. The eyes of an individual that died of unrelated, nonocular reasons were studied histologically and by immunohistochemistry. Scotopic, mixed rod-cone, and photopic electroretinography (ERG) responses were recorded using the 'QuickRetCheck' (n = 6) and 'Dog diagnostic' (n = 5) protocols of the Handheld Multispecies ERG (HMsERG).

RESULTS

The fundus of the peccary is atapetal, with varying amounts of pigmentation seen ophthalmoscopically, and histologically in the retinal pigment epithelium (RPE) and choroid. The retina is holangiotic with dichotomously branching vessels. These cross, and apparently loop on, the optic disk surface, but no venous circle was seen. Immunohistochemistry suggests a high concentration of cone photoreceptors with red/green cones being more abundant than blue cones. Rod ERG responses were very low with no evident dark adaptation. Mixed rod-cone and cone ERG response amplitudes were low compared to those of domestic pigs, but quite similar to those of minipigs.

CONCLUSIONS

To the best of our knowledge, this study describes the collared peccary's retinal features for the first time. A comparison of our findings with data from other ungulate species shows some similarities between the peccary and pig retinas. Further studies are warranted to determine whether the peccary can be used alongside the pig as an animal model in retinal studies.

Assessment of Safety and Functional Efficacy of Stem Cell-Based Therapeutic Approaches Using Retinal Degenerative Animal Models

Dysfunction and death of retinal pigment epithelium (RPE) and or photoreceptors can lead to irreversible vision loss. The eye represents an ideal microenvironment for stem cell-based therapy. It is considered an “immune privileged” site, and the number of cells needed for therapy is relatively low for the area of focused vision (macula). Further, surgical placement of stem cell-derived grafts (RPE, retinal progenitors, and photoreceptor precursors) into the vitreous cavity or subretinal space has been well established. For preclinical tests, assessments of stem cell-derived graft survival and functionality are conducted in animal models by various noninvasive approaches and imaging modalities. In vivo experiments conducted in animal models based on replacing photoreceptors and/or RPE cells have shown survival and functionality of the transplanted cells, rescue of the host retina, and improvement of visual function. Based on the positive results obtained from these animal experiments, human clinical trials are being initiated. Despite such progress in stem cell research, ethical, regulatory, safety, and technical difficulties still remain a challenge for the transformation of this technique into a standard clinical approach. In this review, the current status of preclinical safety and efficacy studies for retinal cell replacement therapies conducted in animal models will be discussed.

A Pharmacodynamic Analysis of Choroidal Neovascularization in a Porcine Model Using Three Targeted Drugs

Purpose

To compare the efficacy of microneedle-delivered suprachoroidal (SC) pazopanib to intravitreal (Ivit) delivery of pazopanib, bevacizumab, or a fusion protein hI-con1 versus vehicle controls on choroidal neovascularization (CNV) growth in a pig model.

Methods

Forty-one pigs were injected on the day of CNV induction (hI-con1 on postinduction day 14) with either 2.5 mg Ivit bevacizumab (n = 9), 1 mg Ivit pazopanib (n = 9), 300 Ivit μg hI-con1 (n = 4), or 1 mg SC pazopanib (n = 9), vs. 10 vehicle controls (3 SC + 7 Ivit = 10). Pigs were euthanized at week 2 (11), 3 (8), 4 (11), and 8 (11), and eyes were fixed for histology. The size of the CNV was determined from histology, and CNV height was the primary outcome measure. Immunostaining for cytotoxic T-cells was performed in the hI-con1 study.

Results

In 39 of 41 (95%) eyes, type 2 CNV lesions were identified. One CNV lesion was lost during dissection. One animal was euthanized due to surgical complications. For mean CNV size comparisons, Ivit pazopanib had smaller mean height measurements (90 ± 20 μm) versus controls (180 ± 20 μm; P = 0.009), and Ivit pazopanib had smaller maximum CNV height (173 ± 43 μm) compared to SC pazopanib (478 ± 105 μm; P = 0.018). The mean lesion size in hI-con1-treated animals trended smaller than in controls (P = 0.11). Immunostaining did not detect cytotoxic T-cells.

Conclusions

Intravitreal pazopanib and to a lesser extent hI-con1 reduced the size of CNV lesions. The pig model has nearly a 100% rate of type 2 CNV induction and is a reliable preclinical model with pharmacodynamics similar to humans.

Time-Dependent Decline in Multifocal Electroretinogram Requires Faster Recording Procedures in Anesthetized Pigs

Purpose

The time-dependent effect of anesthetics on the retinal function is debated. We hypothesize that in anesthetized animals there is a time-dependent decline that requires optimized multifocal electroretinogram (mfERG) recording procedures.

Methods

Conventional and four-frame global-flash mfERG recordings were obtained approximately 15, 60, and 150 minutes after the induction of propofol anesthesia (20 pigs) and isoflurane anesthesia (nine pigs). In six of the propofol-anesthetized pigs, the mfERG recordings were split in 3-minute segments. Two to 4 weeks after initial recordings, an intraocular injection of tetrodotoxin (TTX) was given and the mfERG was rerecorded as described above. Data were analyzed using mixed models in SAS statistical software.

Results

Propofol significantly decreases the conventional and global-flash amplitudes over time. The only significant effect of isoflurane is a decrease in the global-flash amplitudes. At 15 minutes after TTX injection several of the mfERG amplitudes are significantly decreased. There is a linear correlation between the conventional P1 and the global-flash DR mfERG-amplitude (R² = 0.82, slope = 0.72, P < 0.0001). There is no significant difference between the 3-minute and the prolonged mfERG recordings for conventional amplitudes and the global-flash direct response. The global flash–induced component significantly decreases with prolonged mfERG recordings.

Conclusions

A 3-minute mfERG recording and a single stimulation protocol is sufficient in anesthetized pigs. Recordings should be obtained immediately after the induction of anesthesia. The effect of TTX is significant 15 minutes after injection, but is contaminated by the effect of anesthesia 90 minutes after injection. Therefore, the quality of mfERG recordings can be further improved by determining the necessary time-of-delay from intraocular injection of a drug to full effect.

Translational Relevance

General anesthesia is a possible source of error in mfERG recordings. Therefore, it is important to investigate the translational relevance of the results to mfERG recordings in children in general anesthesia.

RETINAL PIGMENT EPITHELIAL TEAR AND ANTI-VASCULAR ENDOTHELIAL GROWTH FACTOR THERAPY IN EXUDATIVE AGE-RELATED MACULAR DEGENERATION: Clinical Course and Long-Term Prognosis

BACKGROUND

To document the long-term outcome in cases of retinal pigment epithelial (RPE) tears after treatment of vascularized pigment epithelial detachments with anti-vascular endothelial growth factor therapy.

METHODS

A retrospective analysis of the long-term outcome of a consecutive series of eyes with RPE tear developed during anti-vascular endothelial growth factor therapy for pigment epithelial detachment associated with choroidal neovascularization or retinal angiomatous proliferation (vascularized pigment epithelial detachment) was performed. Best-corrected visual acuity (BCVA), spectral domain optical coherence tomography, and autofluorescence images and also fluorescein angiograms were analyzed to determine the functional and morphologic development over time.

RESULTS

The long-term outcome of 22 eyes (21 patients, 13 women and 8 men; 65-85 years; mean: 76 years) with RPE tear was performed with minimal follow-up of 3 years (range: 3-5 years, mean: 44 months) and re-treatment with different therapeutic strategies. The eyes were differentiated in 2 groups according to the course of BCVA after the first 2 years of follow-up: Group 1 (11 eyes) demonstrated a stabilized or improved BCVA after 2 years and Group 2 (11 eyes) demonstrated a decrease in BCVA after 2 years. The initial BCVA between both groups was comparable. Also the mean initial size of the RPE tear was the same between the 2 groups, the area of the RPE tear decreased continuously during follow-up in Group 1, whereas this was the case in Group 2 only at the beginning of treatment with a further increase of the size of the RPE tear with longer follow-up. This corresponded with a different morphologic development between the two groups. In Group 1, increasing recovery of autofluorescence at the RPE-free area was visible beginning from the outer border, whereas in Group 2, further growth of the neovascular complex in the area of the RPE tear was observed resulting in larger fibrovascular scars. In addition, in both groups, the development of hyperreflective tissue was seen on spectral domain optical coherence tomography in the RPE-free area. The major therapeutic difference between the 2 groups was a significantly larger number of injections especially during the first year in Group 1.

CONCLUSION

The development of RPE tear after anti-vascular endothelial growth factor therapy for vascularized pigment epithelial detachment in exudative age-related macular degeneration does not necessarily result in large disciform scars and functional loss, but multiple injections seem to be beneficial especially in the first year. With this strategy, RPE tears seem to be covered by autofluorescent and hyperreflective tissue and a regrowth of the neovascular complex can be prohibited. As a result, photoreceptor cells regain their metabolic support with functional recovery.

Metabolic and functional changes in retinitis pigmentosa: comparing retinal vessel oximetry to full-field electroretinography, electrooculogram and multifocal electroretinography

PURPOSE

To determine a relationship between the retinal vessel saturation alterations and the residual retinal function measured by means of full-field electroretinography (full-field ERG), electrooculogram (EOG) and multifocal electroretinography (mfERG) in patients with retinitis pigmentosa (RP).

METHODS

Retinal vessel oximetry (RO), full-field ERG, EOG and mfERG were performed on 43 eyes of 22 patients suffering from RP and were compared to those of 26 eyes of 13 healthy controls. The oxygen saturation in the first and second branch retinal arterioles (A-SO2 ) and venules (V-SO2 ) was measured, and their difference (A-V SO2 ) was calculated. Full-field ERG amplitudes, EOG parameters and averaged mfERG response amplitudes (within central 3°, between 3° and 8°, 8° and 15°, 15° and 24°) were evaluated in relation to the RO measurements.

RESULTS

V-SO2 correlated negatively with the full-field ERG and EOG values, with increasing functional damage the V-SO2 was higher. The RP group was well distinguished from the controls when the RO measurements were correlated to the averaged N1 (baseline to trough), but also to the N1P1 (trough-to-peak) mfERG response amplitudes. Receiver operating characteristic (ROC) curve of V-SO2 , compared to those of N1 and N1P1 mfERG response averages (15-24°), presented a high differential margin between RP and controls (p < 0.001), shown by an area under the ROC curve of 0.912 (95% CI: 0.840-0.984).

CONCLUSION

Retinal vessel saturation showed a significant relation to full-field ERG, EOG and mfERG. Thus, retinal vessel oximetry could potentially complement electrophysiological tests in monitoring disease progression in patients with RP.