Chromovitrectomy is a general term for procedures that use vital dyes to visualize translucent intraocular tissues such as the internal limiting membrane (ILM), vitreous, and epiretinal membrane (ERM) during pars plana vitrectomy (PPV).
The main tissues that require staining during surgery are the following three:
Blue or green dyes are commonly used because they provide high contrast against the orange-red color of the retinal pigment epithelium (RPE), improving visibility of the stained area.
There are three main methods for injecting the dye.
The ILM and epiretinal membrane are semi-transparent tissues only a few micrometers thick, making them difficult to identify under a surgical microscope without staining. Using dye clarifies tissue boundaries, improving the precision and safety of peeling.
The main indications for chromovitrectomy are as follows:
The efficacy of ILM peeling in macular hole surgery has been demonstrated in multiple studies.
In the FILMS trial, the anatomical closure rate was 84% in the ILM peeling group and 48% in the non-peeling group, showing a significant difference (P<0.001)3). Since the ILM serves as a scaffold for cell proliferation, failure to remove it may allow cell proliferation to resume2).
A meta-analysis of 5480 cases showed that ILM peeling significantly reduced the reopening of macular holes2). Surgery with ILM peeling has a lower recurrence rate1). Additionally, five RCTs have investigated the extent of ILM peeling3), and research on optimizing the peeling area is ongoing.
Air-Fluid Exchange Method
Procedure: After fluid-air exchange, the dye is dripped onto the posterior pole.
Advantages: Allows concentrated staining of the posterior pole. Avoids exposure of the peripheral retina to the dye.
Cautions: Requires proficiency in operating under air.
Fluid-Filled Method
Procedure: The dye is injected while the eye is filled with BSS.
Advantages: The technique is simple and easy to learn.
Note: There is a risk of dilution and extensive exposure. This can be managed by using a high-density suspension.
The standard peeling technique after staining is the pinch and peel method 3). Grasp the ILM with fine forceps and peel it in a circular manner. A staining time of 5 to 10 seconds is sufficient 3), and excessive exposure increases the risk of toxicity.
The air-fluid exchange method can confine the staining agent to the posterior pole, avoiding unnecessary exposure to the periphery, and is therefore safer. However, in either method, it is important to keep the staining time to about 5 to 10 seconds and avoid excessive exposure 3).
The main characteristics of each staining agent are shown below.
| Staining agent | Main target tissue | Concentration used |
|---|---|---|
| BBG | ILM (selective) | 0.025% |
| TA | Vitreous/ILM | 40 mg/mL suspension |
| ICG | ILM (high affinity) | 0.05–0.5% |
| TB | Epiretinal membrane (high affinity) | 0.15% |
ILM Staining Dyes
BBG (Brilliant Blue G): Selective affinity for ILM3). Epiretinal membrane and vitreous are almost unstained. No retinal toxicity. Neuroprotective effects have also been suggested.
ICG (Indocyanine Green): High affinity for type IV collagen and laminin in the ILM3). First ILM staining dye used3). Toxicity concerns exist.
Epiretinal Membrane Stains
TB (Trypan Blue): High affinity for staining epiretinal membranes. Selectively stains glial cells in the epiretinal membrane. Low affinity for ILM and vitreous. Corneal endothelial toxicity at high concentrations.
Vitreous Visualization
TA (Triamcinolone Acetonide): Deposits in the vitreous as white crystals, visualizing the vitreous 3). Not a stain but provides contrast as white crystals on the ILM. Also has anti-inflammatory effects.
A white crystalline aqueous suspension (40 mg/mL), used by injecting 0.1–0.3 mL. It whitens the vitreous and posterior vitreous cortex. Unlike stains, it provides contrast by depositing as white crystals on the ILM 3). It also has anti-inflammatory effects, helping to suppress postoperative intraocular inflammation. The half-life is about 18 days in non-vitrectomized eyes and about 3 days in vitrectomized eyes. Side effects include cataract progression and increased intraocular pressure. In Japan, MacuAid (triamcinolone acetonide 40 mg/mL) is approved.
A blue food dye-derived stain with selective affinity for the ILM 3). It does not stain the epiretinal membrane or vitreous, so it is used only during ILM peeling. The working concentration is 0.025% (0.25 mg/mL) in an isotonic solution. In vitro and in vivo studies have shown no retinal toxicity, and neuroprotective effects have been suggested. TB and BBG were developed after ICG and have better safety profiles 3).
In Japan, a preparation method involves dissolving 0.1 g of powder in 400 mL of BSS and sterilizing by autoclaving at 115°C for 30 minutes. The shelf life is said to be 3 months after preparation.
A blue organic dye with high staining affinity for ERM. It stains cellular components of the ERM by passing through damaged cell membranes of dead cells, making it suitable for ERM peeling surgery. It has low affinity for the ILM and vitreous. The working concentration is 0.15%, and making it a high-density solution (mixing TB with 10% glucose at a 3:1 ratio) facilitates concentration at the posterior pole. Corneal endothelial toxicity has been reported at high concentrations, and it is teratogenic, so it should be avoided during pregnancy and in children.
A green dye with high affinity for type IV collagen and laminin, which constitute the ILM 3). It was the first dye used for ILM staining 3). A partial “peeling” effect (pseudo-peeling effect) on the ILM has also been reported 3). However, concerns about toxicity to the inner retina, optic nerve, and visual field defects exist 3), and current recommendations are to use low concentrations, minimal exposure time, and minimized illumination 3). Initial dilution requires distilled water (precipitation occurs in saline), followed by adjustment to final concentration with BSS. The FDA has approved it only for intravenous use; intraocular use is off-label.
TA is approved in Japan as MacuAid. BBG and ICG have no officially approved intraocular products in Japan and are used as self-prepared or off-label. TB is also often used off-label. It is necessary to check the facility’s pharmaceutical management regulations before use.
The following factors are involved in the development of toxicity.
| Cause of toxicity | Relevant dye | Countermeasure |
|---|---|---|
| High or low osmolarity | ICG (low osmolarity is problematic) | Prepare in isotonic solution |
| Phototoxicity | ICG | Minimize illumination |
| Preservative toxicity | All formulations | Choose preservative-free formulation |
| Excessive exposure time | ICG, TB | Wash out within 5–10 seconds |
Regarding osmotic issues, a hypo-osmotic environment may cause retinal damage due to Ca²⁺ influx. Conversely, hyperosmolarity leads to retinal contraction. One cause of ICG toxicity is thought to be injection under hypo-osmotic conditions3), so preparation in an isotonic solution is important.
Regarding preservative issues, myristyl-γ-picolinium chloride has been reported to cause severe toxicity, and preservative-free formulations are preferable. Data on benzyl alcohol are currently unclear.
Characteristic findings after ILM peeling include the following:
The toxicity of ICG involves multiple factors. These include Ca²⁺ influx due to injection under low osmotic pressure, photo-oxidation reactions (phototoxicity) from light exposure, and the involvement of iodine components contained in the dye 3). To reduce these risks, it is recommended to use low concentrations, short exposure times, minimize illumination, and prepare the dye in isotonic solutions 3).
Research on new vital dyes is ongoing to overcome the toxicity and selectivity issues of existing dyes.
This is a technique that promotes closure of macular holes by inverting a part of the ILM (as a flap) rather than removing it completely 3). It is being considered for use in large macular holes or refractory cases. Visualization of the ILM with vital dyes contributes to the precision of this technique.
For evaluating new vital dyes and techniques, the introduction of a stepwise surgical innovation evaluation framework such as the IDEAL framework is required. Systematic evaluation of safety and efficacy remains a future challenge.
Bromophenol blue is a candidate staining agent that can stain both ILM and ERM and is considered less toxic than ICG. Additionally, IFCG (sodium iodide-free derivative) is being studied with a design that removes the iodine component, which is thought to contribute to ICG toxicity. Both are currently in clinical trial stages and have not yet reached standard use.
