NONAXOPLASMIC TRANSFER OF INDOCYANINE GREEN INTO THE OPTIC NERVE AFTER INTRAVITREAL APPLICATION

Brilliant blue G assisted macular surgery: the effect of air infusion on contrast recognisability in internal limiting membrane peeling

BACKGROUND

To evaluate the potential efficacy and safety of inner limiting membrane (ILM) staining with brilliant blue G (BBG) under air infusion.

METHODS

63 patients, treated by one surgeon with macular hole or idiopathic epiretinal membrane were evaluated prospectively. BBG was applied under air infusion in 38 patients (group 1), and injected into the vitreous cavity in 25 (group 2). Main outcome measures were the chromaticity difference between the stained ILM and the unstained underlying retina, anatomical-functional outcomes and complications of the surgery. Chromaticity difference was measured by an objective and quantitative analysis method to describe colour contrast strengths as they are perceived by the human eye. Anatomical and functional outcomes were assessed using optical coherence tomography (OCT), visual field analyses (VFA) and multifocal electroretinography (mfERG).

RESULTS

CIELAB scores showed a significantly superior contrast for group 1 (16.72±2.36) than group 2 (10.34±1.29) (p<0.001). Visual acuity had increased in 28 eyes and remained stable in 10 eyes in group 1. In group 2, visual acuity had improved in 17 patients and remained unchanged in 8 patients. Based on postoperative OCT, anatomical success rate was 100%. During the follow-up period, mfERG and VFA demonstrated no case of BBG toxicity in either group. Cataract progression was the main postoperative complication (six eyes in group 1 and four eyes in group 2) and did not show a significant difference between the groups (p=0.45).

CONCLUSIONS

BBG under air infusion yields a significantly higher contrast staining and easy peeling of ILM associated with anatomical and functional improvement and no retinal toxicity after macular surgery.

Mapping the surface astrocytes of the optic disc: a fluid-conducting role of the astrocytic covering of the central vessels

BACKGROUND

The vitreous interface of the optic nerve has been studied to delimit the covering of Elschnig's astrocytes and interstitial pathways of flow through the prelaminar region.

METHODS

Perfusion of the prelaminar tissue under controlled pressure with a fluorescent marker injected into the vitreous cavity in pig eyes. The prelaminar region of the optic nerve and adjacent retina was fixed and flatmounted or frozen and cryosectioned and examined with the confocal laser microscope. Samples were also prepared for conventional transmission electron microscopy.

RESULTS

The surface of the vitreous surface of the optic nerve is covered by a cobblestone-like pavement made of astrocytic projections. Intensely stained passages of different thickness indicate the presence of wide interconnected intercellular spaces in the covering of Elschnig's astrocytes. Those passages are absent in the intervascular areas occupied by axons and axon-linked astrocytes.

CONCLUSIONS

Delineation of the astrocytic pavement and the preferred flow routes formed by wide extracellular spaces are conspicuous features of the prelaminar region when examined with the confocal laser microscope and the help of sticky fluorescent tracer. This suggests that excess extracellular fluid can be interchanged with the vitreous by a network of interconnected extracellular spaces or preferred flow routes. Some pathogenic mechanisms can be related to fluid interchange in the optic nerve head.

Fenestrations and preferential flow routes in the prelaminar optic nerve through wet scanning electron microscope and perfusion of tracers

PURPOSE

We study the vitreous interface of the optic disc to delimit the passages for the flow of fluids through the prelaminar tissue of porcine eyes.

METHODS

Wet scanning electron microscope (SEM), conventional SEM and transmission electron microscope (TEM) were used to explore the surface of the optic nerve of the pig. The vitreous cavity was perfused with a fluorescent marker and colloidal gold at controlled pressure. Samples of perfused optic nerve head were cryosectioned and observed with the confocal laser microscope (lectin) or resin embedded and observed under TEM (gold).

RESULTS

Fenestrations were present under the SEM in all three regions of the vitreous interface. SEM results were confirmed at the TEM level and under the wet-SEM. Perfusion experiments traced the flow of a fluorescent molecule delineating routes of preferential flow with origin in the fenestrations. Colloidal gold marked the site of entrance in the prelaminar tissue identifying major fenestrations in the basal membrane.

CONCLUSIONS

Interchange of fluid between the optic nerve and the vitreous cavity in the pig is facilitated by fenestrations of varied sizes in the basal membrane and preferential flow routes through the prelaminar tissue. Preferential flow routes exist in the extracellular spaces of Elschnig and Kuhn' astrocytes and give a sharply distinct image when compared with flow through zones in which astrocytes envelope axons. Escape routes may be instrumental in preventing oedemas of the optic nerve head, but they could also serve as entrance doors for fluids from the vitreous and aqueous and play a pathogenic role in ageing and glaucoma.

Vital staining with indocyanine green: a review of the clinical and experimental studies relating to safety

Indocyanine green (ICG) is extremely effective when used as a vital stain during macular hole surgery. By staining the internal limiting membrane, ICG facilitates removal of this delicate and sometimes hard to visualize structure. There is, however, considerable debate regarding its safety. This review considers the clinical and experimental studies of ICG and a related agent, infracyanine green. Some clinical papers show visual field defects, reduced visual acuity, and persistence of ICG at the macula and optic nerve. Other clinical studies fail to demonstrate toxicity. The experimental studies are also conflicting, but there are emerging trends. These suggest that surgeons who continue to use ICG should use concentrations not greater than 0.05 mg/ml, in fluid-filled eyes, with short exposure times, iso-osmolar solutions, and avoid proximal or prolonged endoillumination of stained tissue. A smaller number of studies suggest that infracyanine green produces similar staining to ICG, and may possibly be safer, but there are too few well-designed studies to reach a conclusion. Although the use of ICG continues, on the balance of evidence, this review suggests that it is has the potential to produce subtle visual damage.

Surgical outcome after removal of idiopathic macular epiretinal membrane in young patients

PURPOSE

To report the clinical features of the eye of young patients with an idiopathic macular epiretinal membrane (ERM), and the visual outcomes after the surgical removal of the ERM.

METHODS

A retrospective review of the medical records of eight young patients (age, 23-39 years; mean, 32.5 years) with an idiopathic macular ERM was performed. The patients underwent vitrectomy and removal of the ERM with peeling of the internal limiting membrane (ILM). The pre- and postoperative visual acuity and intra- and postoperative complications were investigated.

RESULTS

Ophthalmoscopically, the ERMs in seven eyes were white, opaque, and dense, while one was grayish-white and less dense. A posterior vitreous detachment was not present and the ERM adhered strongly to the underlying retina in all eight eyes. The mean best-corrected visual acuity (BCVA) preoperatively was 20/140 (Snellen; range: 20/250-20/63), and the BCVA improved significantly to 20/30 (range: 20/40-20/20) postoperatively with an average follow-up of 14.6 months (range: 6-42 months; Wilcoxon sign-rank test, P<0.001). An improvement of >7 lines was observed in seven of eight eyes. A recurrence of an ERM without involving the macula was detected in one eye (12.5%).

CONCLUSIONS

The clinical features of the ERMs in young patients are different from those in elderly patients, eg, thicker, more adherent to the retina, and still attached to the vitreous. Vitrectomy and removal of ERM with ILM peeling are effective and safe surgical procedures. Removal of the ILM may minimize the recurrence of an ERM.

Residual indocyanine green fluorescence pattern after vitrectomy for idiopathic macular hole with internal limiting membrane peeling

BACKGROUND

Internal limiting membrane (ILM) peeling with indocyanine green (ICG) staining is a commonly used procedure to treat idiopathic macular holes (MH).

AIM

To report changes in the patterns of residual ICG fluorescence over time after vitrectomy using the Heidelberg Retina Angiograph 2 (HRA2, Heidelberg Engineering, Heidelberg, Germany).

METHODS

10 patients (10 eyes) who had undergone vitrectomy for MH with ILM peeling were included. 9 (90%) patients underwent ILM peeling with ICG, and 1 (10%) patient had it with triamcinolone acetonide (TA). We observed residual ICG using HRA2, postoperatively. Autofluorescence, optical coherence tomography images and best-corrected visual acuity (BCVA) measurements were also obtained. The minimal follow-up was 3 months.

RESULTS

The MHs were closed postoperatively in all patients (100%). In eyes that underwent ILM peeling with ICG, the BCVA improved significantly (p<0.001) in 8 (89%) eyes and was unchanged in 1 (11%) eye. HRA2 showed the ICG fluorescence patterns but not TA postoperatively. The ICG hyperfluorescent signal was typically diffuse at the posterior retina and was hypofluorescent around the fovea. The hyperfluorescence then migrated towards the optic nerve disc presumably along the nerve fibre, and the area of ILM peeling was clearly identified. A large number of hyperfluorescent dots were observed instead of diffuse hyperfluorescence that was observed just after surgery.

CONCLUSIONS

Patterns of residual ICG fluorescence were sequentially observed with HRA2 after vitrectomy for MH with ICG-assisted ILM peeling.

Comparison of ICG-assisted ILM peeling and triamcinolone-assisted posterior vitreous removal in diffuse diabetic macular oedema

AIM

To compare the effect of indocyanine green (ICG)-assisted internal limiting membrane (ILM) peeling and triamcinolone acetonide-assisted posterior vitreous removal on visual acuity in patients with diffuse diabetic macular oedema (DMO).

METHODS

In total, 24 patients with diffuse DMO who underwent pars plana vitrectomy were included in this study. In all, 11 patients (mean age 57 years) were performed ICG-assisted ILM peeling; while 13 patients (mean age 54 years) underwent triamcinolone-assisted posterior vitreous removal. Patients from two different treatment regimens were compared in terms of best-corrected visual acuity (BCVA) at postoperative sixth months.

RESULTS

In ICG-assisted ILM peeling group, preoperative BCVA (1.3+/-0.4, mean+/-SD, logMAR) improved postoperatively to 0.9+/-0.5 (P=0.011). In eyes underwent triamcinolone-assisted posterior vitreous removal, baseline BCVA of 1.4+/-0.4 improved to 1.0+/-0.5 (P=0.007). There was no difference between baseline as well as postoperative sixth-month BCVA results of both groups (P=0.59 and P=0.57, respectively).

CONCLUSIONS

Triamcinolone-assisted posterior vitreous removal and ICG-assisted ILM peeling have the same effect in terms of postoperative BCVA in patients with diffuse DMO.