Investigation of the retinal biocompatibility of acid violet for chromovitrectomy

Temperature control during pars plana vitrectomy

PURPOSE

To evaluate the impact of temperature-controlled pars plana vitrectomy (PPV) on structural and functional outcomes in a rabbit eye model in vivo.

METHODS

Ten healthy New Zealand White rabbits underwent temperature-controlled PPV in the right eye (group A), using a device specifically designed to heat the infusion fluid/air and integrated into the vitrectomy machine, and conventional PPV in the left eye (group B). Both eyes received ophthalmic examination and electroretinography (ERG) before and 1 week postoperatively. After 1-week ERG, rabbits were enucleated and then sacrificed. Histological and immunohistochemical examinations were performed on enucleated eyes and expression of glial fibrillary acidic protein (GFAP) and vimentin investigated.

RESULTS

Postoperatively, only group B showed significantly decreased amplitude and increased latency of a-wave at 3 cd·s/m2 (p = 0.001 and 0.005, respectively). Significant increase of b-wave latency at 0.01 cd·s/m2 was detected in both groups (p = 0.019 and 0.023, respectively). Postoperatively, amplitude of oscillatory potentials (OPs) increased significantly in group A (p = 0.023) and decreased in group B. In both groups, OPs latency significantly increased at 1-week test (P < 0.05). A greater number of eyes without structural retinal alterations was detected in group A compared to group B (6 vs 5, respectively). GFAP expression was higher in group B than group A, even if the difference was not statistically significant.

CONCLUSION

Temperature-controlled PPV resulted in more favorable functional and structural outcomes in rabbit eyes compared with conventional PPV, supporting the potential beneficial role of the intraoperative management of intraocular temperature in vitreoretinal surgery.

Spotlight on the Internal Limiting Membrane Technique for Macular Holes: Current Perspectives

Pars plana vitrectomy has become the standard procedure for primary macular holes (MHs) repair, including the removal of the posterior cortical vitreous, the stripping of eventual epiretinal membranes, and finally an intraocular gas tamponade. During this procedure, peeling the internal limiting membrane (ILM) has been proven to increase closure rates and avoid postoperative reopening in several researches. In fact, even in large MHs more than 400 µm, the advantage of peeling off the ILM was highlighted by better anatomical closure rates. Nevertheless, some authors suggested that ILM peeling is not always essential, because it generates various side effects in retinal structure and function. Furthermore, the ideal amount of ILM peeling and the most effective strategies for removing the ILM are still subject of research. Different surgical modifications have been reported as alternatives to traditional peeling in certain clinical settings, including ILM flaps, ILM scraping, and foveal sparing ILM peeling. As regards large MHs, the introduction of ILM inverted flap appeared as a game changer, offering a significantly higher >90% closure rate when compared to traditional ILM peeling. Modifications to inverted ILM flap procedures have been claimed in recent years, in order to define the best area and direction of ILM peeling and its correlation with functional outcomes. Moreover, several innovations saw the light in the setting of recurrent MHs, such as ILM free flap transposition, inverted ILM flap combined autologous blood clot technique, neurosensory retinal flap, and human amniotic membrane (HAM) plug, claiming higher anatomical success rate also in those complex settings. In conclusion, the aim of this review is to report how the success rate of contemporary macular surgery has grown since the turn of the century, especially for big and chronic MHs, analyzing in which way ILM management became a crucial point of this kind of surgery.

NEGATIVE EFFECTS OF VITAL DYES AFTER UNEVENTFUL VITREOMACULAR SURGERY

PURPOSE

Vital dyes have become a clinical standard during chromovitrectomy but toxicity remains an issue. We compared the clinical outcome of one supposedly toxic vital dye (AV 17 with 5% mannitol) with a standard vital dye (MBB Dual) and performed a power analysis for future comparative studies.

METHODS

Retrospective analysis of 270 eyes after chromovitrectomy with internal limiting membrane peeling because of macular holes. Primary endpoint was loss in BCVA >2 lines and photoreceptor atrophy as seen on optical coherence tomography examination.

RESULTS

In 173 eyes, staining of the epiretinal membrane and extracellular matrix was performed using MBB (Group A), and in 97 using AV 17-M (Group B). The mean BCVA was not significantly different after more than 3 months and also not in the early postoperative period after surgery between Group A and Group B. The number of patients suffering from a decline in BCVA of two lines and more was not significantly higher in patients of Group B. There was not a significantly higher percentage of patients with an inner segment/outer segment defect.

CONCLUSION

Our rather homogeneous study showed no significant difference between both dyes. Thousand five hundred patients would need to be examined to find a significant difference in future studies.

Retinal Toxicity of Acai Fruit (Euterpe Oleracea) Dye Concentrations in Rabbits: Basic Principles of a New Dye for Chromovitrectomy in Humans

PURPOSE

Evaluate toxicity of acai fruit (Euterpe oleracea) dye concentrations in a rabbit model.

METHODS

Rabbits were injected intravitreously with 10%, 25%, and 35% acai dye concentrations. Control eyes received balanced salt solution (BSS). Electroretinogram (ERG), fundus imaging, fluorescein angiography (FA), optical coherence tomography (OCT), and light and transmission electron microscopy (LM/TEM) were performed.

RESULTS

Fundus imaging showed increased vitreous opacity with increased dye concentrations. FA and OCT showed normality with all concentrations. Comparisons between BSS and dye concentrations were analyzed using Kruskal-Wallis and Mood's median test (p < 0.05). At 24 h, ERGs showed reduced amplitudes from baseline in all eyes. Median b-wave amplitudes nonsignificantly decreased and latency increased with 10% and 25%; findings were significant (p < 0.05) for 35%. LM and TEM showed no abnormalities for 10% and 25%. With 35%, TEM showed ganglion cell edema at 24 h that resolved after 7 days. Vacuolization, multilamellar bodies, and nerve bundle damage occurred at 24 h/7 days in the inner nuclear layer. Mitochondrial cristae disruption occurred in the inner photoreceptor segment at 24 h that decreased by 7 days.

CONCLUSION

Ten and twenty-five percent concentrations were safe and may improve identification of the posterior hyaloid and internal limiting membrane during chromovitrectomy in humans.

Negative Effects of Acid Violet-17 and MBB Dual In Vitro on Different Ocular Cell Lines

PURPOSE

Vital dyes have become a clinical standard during vitrectomy to visualize anatomical structures. It was the aim of this study to test the effect of two vital dyes (AV 17-M with 5% mannitol and MBB Dual) on different intraocular cells, to see whether in vitro test can be used as reliable preclinical testing tool.

METHODS

Cell morphology was assessed via phase contrast pictures, cell viability via MTS assay and total cell amount via crystal violet staining. ARPE19 and 661W cells were chosen for toxicology testing at different exposure times (60 seconds, 15 minutes and 30 minutes). Vital dyes were completely removed after the staining period.

RESULTS

Treatment with AV 17-M changed the morphology and the cell number at every time point investigated on ARPE19 and 661 W cells. ARPE19 cells treated with AV 17-M or MBB Dual displayed only a slight or no decrease in cell viability after the three different exposure times. AV-17 without medium to simulate a possible intraoperative use after fluid-air exchange showed a decrease in viability of 6%, 24% and 14%. A difference in cell density of 21%, 46% and 34% was noted after CV staining for AV 17-M, MBB Dual led to a decrease of 2%, 16% and 3% after 30 minutes compared to BSS. AV 17-M directly applied on 661W decreased viability significantly by 18% after 60 seconds, 33% after 15 minutes and 40% after 30 minutes. Cell density of 661W cells exposed relevant negative effects; after incubation of 60 seconds with AV 17-M, the cell amount was significantly lowered by 41% and MBB Dual by 12%. After 15 minutes, a loss of 48% cell amount was detected with AV 17-M and after 30 min 51%. MBB Dual led to 37% loss after 15 minutes and to 28% loss after 30 minutes.

CONCLUSION

AV 17-M with 5% mannitol has a negative effect on different ocular cells.

Biocompatibility of the vital dye Acid Violet-17 on retinal pigment epithelial cells

Purpose

To examine the viability and differentiation of retinal pigment epithelial (RPE) cells after exposure to the vital dye Acid Violet-17 (AV-17).

Methods

Bovine RPE cells were incubated with AV-17 (0.0625–0.5 mg/mL) for 30 seconds or 5 minutes. Viability was determined by live/dead staining, cleaved CASP3 immunostainings, and MTT test. Actin cytoskeleton was visualized by Alexa 488-phalloidin. Immunocytochemistry was performed to determine the levels of ZO-1, CTNNB1, and KRT19.

Results

Exposure to AV-17 at the concentrations of 0.25–0.5 mg/mL resulted in a dose-dependent decrease in viability, the loss of ZO-1 from tight junctions, translocation of CTNNB1 into the cytoplasm and nucleus, disarrangement of the actin cytoskeleton, and a slight increase in KRT19.

Conclusion

AV-17 at a concentration <0.125 mg/mL is likely to be well tolerated by the RPE cells, whereas the concentrations from 0.25 mg/mL onward can reduce viability and induce dedifferentiation particularly after long-term exposure.

An evaluation of two heavier-than-water internal limiting membrane-specific dyes during macular hole surgery

PURPOSE

To evaluate the staining characteristics and effect on internal limiting membrane (ILM) histology of two heavier-than-water ILM-specific dyes during macular hole surgery: acid violet 17 combined with 5 % mannitol (AV17-M) and brilliant blue G with 4 % polyethylene glycol (BBG-P).

METHODS

Single-centre observational comparative cohort study. The ILM of consecutive patients undergoing surgery for idiopathic macular hole were stained with BBG-P and AV17-M for 10 s each. The ILMs were retrieved and examined with electron microscopy. The extent of retinal and vitreous side debris was scored. Surgical videos were used to assess the staining contrast effect by measuring the Euclidean distance in the CIELAB colour space between stained and unstained retinas after peeling.

RESULTS

51 consecutive patients were studied with 25 in the AV17-M group and 26 in the BBG-P group. The mean age was 71 years with no significant difference between the groups. The amount of retinal side tissue was greater on the BBG-P-stained ILMs compared to the AV17-M-stained ILMs (30.2 versus 19.6 %, p < 0.001). There was a difference in the CIELAB colour space separation distance between stained and peeled retinas (5.89 versus 3.97, p = 0.01) in favour of BBG-P. Visual outcomes between the two groups were similar (logMAR visual acuity 0.40 versus 0.38, p = 0.74).

CONCLUSION

Both stains were successfully used to peel the ILM with comparable outcomes. AV17-M resulted in less retinal debris than BBG-P, suggesting an altered and potentially beneficial ILM cleavage plane from the retina but with lowered staining contrast than BBG-PEG.

Current Trends about Inner Limiting Membrane Peeling in Surgery for Epiretinal Membranes

The inner limiting membrane (ILM) is the basement membrane of the Müller cells and can act as a scaffold for cellular proliferation in the pathophysiology of disorders affecting the vitreomacular interface. The atraumatic removal of the macular ILM has been proposed for treating various forms of tractional maculopathy in particular for macular pucker. In the last decade, the removal of ILM has become a routine practice in the surgery of the epiretinal membranes (ERMs), with good anatomical results. However many recent studies showed that ILM peeling is a procedure that can cause immediate traumatic effects and progressive modification on the underlying inner retinal layers. Moreover, it is unclear whether ILM peeling is helpful to improve vision after surgery for ERM. In this review, we describe the current understanding about ILM peeling and highlight the beneficial and adverse effects associated with this surgical procedure.

Investigation of new dyes for chromovitrectomy: preclinical biocompatibility of trisodium, orangell and methyl violet

Purpose

To investigate the retinal toxicity by electroretinography (ERG), clinical examination and histology after intravitreal injection of biological stains in two concentrations: Trisodium (0.50 g/L and 1.00 g/L), Orangell (0.25 g/L and 1.00 g/L) and Methyl Violet (0.50 g/L and 1.00 g/L).

Methods

Eighteen New-Zealand albinos rabbits were assigned in six groups (n = 3 in each group). The animals in group 1 received Trisodium in the dose of 0.50 g/L and group 2 received 1.00 g/L; Group 3 received Orangell in the dose of 0.25 g/L and group 4 received 1.00 g/L; Group 5 received Methyl Violet in the dose of 1.00 g/L and group 6 received 0.50 g/L. A volume of 0.05 mL of dye was injected in the right eyes, whereas the left eyes received the same volume of balanced salt solution (BSS) as control. ERG recordings and clinical examination were performed at baseline and seven days after intravitreal injection. The ERG responses at one week after injection were compared with baseline levels. A decrease in the post-injection amplitude of more than 50% was considered remarkable. After the 7-day follow-up, rabbits were euthanized and eye enucleated for light microscopy (LM) histological evaluation.

Results

At clinical examination by indirect ophthalmoscopy seven days after dye injection, all eyes were negative for cataract, hemorrhage, retinal detachment, and intraocular opacities. Amplitude analysis of maximum scotopic b-wave showed no significant reduction in either dye injected or control eyes. Neither dye nor BSS caused significant retinal alteration on LM at doses tested.

Conclusions

Trisodium, Orangell and Methyl Violet can be applied in future studies in order to prove the capacity to stain preretinal tissues and vitreous without toxicity. The three dyes did not induce significant ERG amplitude reduction or LM alterations in this preliminary experimental research. Trisodium, Orangell and Methyl Violet may be potentially useful vital dyes for ocular surgery, and deserve further investigation.